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	<rfc ipr="trust200902" docName="draft-ietf-avtcore-rtp-evc-07" category="std" co	<rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft
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	<title abbrev="RTP payload format for EVC">RTP Payload Format for Essential
	Video Coding (EVC)</title>


		<front>
		<title abbrev="RTP Payload Format for EVC">RTP Payload Format for Essential
		Video Coding (EVC)</title>
		<seriesInfo name="RFC" value="9584"/>
	<author initials="S." surname="Zhao" fullname="Shuai Zhao">	<author initials="S." surname="Zhao" fullname="Shuai Zhao">
	<organization>Intel</organization>	<organization>Intel</organization>
	<address>	<address>
	<postal>	<postal>
	<street>2200 Mission College Blvd</street>	<street>2200 Mission College Blvd</street>

	<city>Santa Clara</city>	<city>Santa Clara</city><region>California</region>
	<code>95054</code>	<code>95054</code>

	<country>USA</country>	<country>United States of America</country>
	</postal>	</postal>
	<email>shuai.zhao@ieee.org</email>	<email>shuai.zhao@ieee.org</email>
	</address>	</address>
	</author>	</author>
	<author initials="S." surname="Wenger" fullname="Stephan Wenger">	<author initials="S." surname="Wenger" fullname="Stephan Wenger">
	<organization>Tencent</organization>	<organization>Tencent</organization>
	<address>	<address>
	<postal>	<postal>
	<street>2747 Park Blvd</street>	<street>2747 Park Blvd</street>

	<city>Palo Alto</city>	<city>Palo Alto</city><region>California</region>
	<code>94588</code>	<code>94588</code>

	<country>USA</country>	<country>United States of America</country>
	</postal>	</postal>
	<email>stewe@stewe.org</email>	<email>stewe@stewe.org</email>
	</address>	</address>
	</author>	</author>
	<author initials="Y." surname="Lim" fullname="Youngkwon Lim">	<author initials="Y." surname="Lim" fullname="Youngkwon Lim">
	<organization>Samsung Electronics</organization>	<organization>Samsung Electronics</organization>
	<address>	<address>
	<postal>	<postal>
	<street>6625 Excellence Way</street>	<street>6625 Excellence Way</street>

	<city>Plano</city>	<city>Plano</city><region>Texas</region>
	<code>75013</code>	<code>75013</code>

	<country>USA</country>	<country>United States of America</country>
	</postal>	</postal>
	<email>yklwhite@gmail.com</email>	<email>yklwhite@gmail.com</email>
	</address>	</address>
	</author>	</author>


	<date year="2023" month="December" day="19"/>	<date year="2024" month="June"/>


	<area>ART</area>	<area>WIT</area>
	<workgroup>avtcore</workgroup>	<workgroup>avtcore</workgroup>

	<keyword>Internet-Draft</keyword>

	<abstract>

	<?line 113?>


	<t>This document describes an RTP payload format for the Essential Video Coding	<keyword>EVC</keyword>
	(EVC) standard, published as ISO/IEC International Standard 23094-1. EVC was dev	<keyword>ISO/IEC 23094-1</keyword>
	eloped by the Moving Picture Experts Group (MPEG). The RTP payload format allows	<keyword>Essential Video Coding</keyword>
	for the packetization of one or more Network Abstraction Layer (NAL) units in e
	ach RTP packet payload and the fragmentation of a NAL unit into multiple RTP pac
	kets. The payload format has broad applicability in videoconferencing, Internet
	video streaming, and high-bitrate entertainment-quality video, among other appli
	cations.</t>


		<abstract>
		<t>This document describes an RTP payload format for the Essential Video
		Coding (EVC) standard, published as ISO/IEC International Standard
		23094-1. EVC was developed by the MPEG. The RTP payload format allows
		for the packetization of one or more Network Abstraction Layer (NAL)
		units in each RTP packet payload and the fragmentation of a NAL unit
		into multiple RTP packets. The payload format has broad applicability in
		videoconferencing, Internet video streaming, and high-bitrate
		entertainment-quality video, among other applications.</t>
	</abstract>	</abstract>


	</front>	</front>


	<middle>	<middle>


	<?line 117?>	<section anchor="introduction">
		<name>Introduction</name>
	<section anchor="introduction"><name>Introduction</name>	<t>The Essential Video Coding <xref target="EVC"/> standard, which is for
		mally designated as ISO/IEC International Standard 23094-1 <xref target="EVC"/>,
	<t>The Essential Video Coding <xref target="EVC"/> standard, which is formally	was published in 2020. One of MPEG's goals is to keep EVC's Baseline profile e
	designated as ISO/IEC International Standard 23094-1 <xref target="ISO23094-1"/>	ssentially royalty-free by using technologies published more than 20 years ago o
	has been published in 2020. One goal of MPEG is to keep <xref target="EVC"/>&#	r otherwise known to be available for use without a requirement for paying royal
	39;s Baseline profile essentially royalty-free by using technologies published m	ties, whereas more advanced profiles follow a reasonable and non-discriminatory
	ore than 20 years ago or otherwise known to be available for use without a requi	licensing terms policy. Both the Baseline profile and higher profiles of EVC <xr
	rement for paying royalties, whereas more advanced profiles follow a reasonable	ef target="EVC"/> are reported to provide coding efficiency gains over High Effi
	and non-discriminatory licensing terms policy. Both the Baseline profile and hig	ciency Video Coding <xref target="HEVC"/> and Advanced Video Coding <xref target
	her profiles of <xref target="EVC"/> are reported to provide coding efficiency g	="AVC"/> under certain configurations.</t>
	ains over High Efficiency Video Coding <xref target="HEVC"/> and Advanced Video	<t>This document describes an RTP payload format for EVC. It shares its ba
	Coding <xref target="AVC"/> under certain configurations.</t>	sic design with the NAL unit-based RTP payload formats of H.264 Video Coding <xr
		ef target="RFC6184"/>, Scalable Video Coding (SVC) <xref target="RFC6190"/>, Hig
	<t>This document describes an RTP payload format for EVC. It shares its basic de	h Efficiency Video Coding (HEVC) <xref target="RFC7798"/>, and Versatile Video C
	sign with the NAL unit-based RTP payload formats of H.264 Video Coding <xref tar	oding (VVC) <xref target="RFC9328"/>. With respect to design philosophy, securi
	get="RFC6184"/>, Scalable Video Coding (SVC) <xref target="RFC6190"/>, High Effi	ty, congestion control, and overall implementation complexity, it has similar pr
	ciency Video Coding (HEVC) <xref target="RFC7798"/>, and Versatile Video Coding	operties to those earlier payload format specifications. This is a conscious ch
	(VVC)<xref target="RFC9328"/>. With respect to design philosophy, security, con	oice, as at least the RTP Payload Format for H.264 video as described in <xref t
	gestion control, and overall implementation complexity, it has similar propertie	arget="RFC6184"/> is widely deployed and generally known in the relevant impleme
	s to those earlier payload format specifications. This is a conscious choice, a	nter communities. Certain mechanisms described in <xref target="RFC6190"/> were
	s at least <xref target="RFC6184"/> is widely deployed and generally known in th	incorporated, as EVC supports temporal scalability. EVC currently does not offe
	e relevant implementer communities. Certain mechanisms known from <xref target=	r higher forms of scalability.</t>
	"RFC6190"/> were incorporated as EVC supports temporal scalability. EVC currentl	<section anchor="overview-of-the-evc-codec">
	y does not offer higher forms of scalability.</t>	<name>Overview of the EVC Codec</name>
		<t>The codings described in <xref target="EVC"/>, <xref target="AVC"/>,
	<section anchor="overview-of-the-evc-codec"><name>Overview of the EVC Codec</nam	<xref target="HEVC"/>, and <xref target="VVC"/> share a similar hybrid video cod
	e>	ec design. In this document, we provide a very brief overview of those features
		of EVC that are, in some form, addressed by the payload format specified herein
	<t><xref target="EVC"/>, <xref target="AVC"/>, <xref target="HEVC"/> and <xref t	. Implementers have to read, understand, and apply the ISO/IEC standard pertain
	arget="VVC"/> share a similar hybrid video codec design. In this document, we p	ing to EVC <xref target="EVC"/> to arrive at interoperable, well-performing impl
	rovide a very brief overview of those features of EVC that are, in some form, ad	ementations. The EVC standard has a Baseline profile and a Main profile, the lat
	dressed by the payload format specified herein. Implementers have to read, unde	ter being a superset of the Baseline profile but including more advanced feature
	rstand, and apply the ISO/IEC standard pertaining to EVC to arrive at interopera	s. EVC also includes still image variants of both Baseline and Main profiles, i
	ble, well-performing implementations. The EVC standard has a Baseline profile an	n each of which the bitstream is restricted to a single IDR picture. EVC facilit
	d a Main profile, the latter being a superset of the Baseline profile but includ	ates certain walled garden implementations under commercial constraints imposed
	ing more advanced features. EVC also includes still image variants of both Base	by intellectual property rights by including syntax elements that allow encoders
	line and Main profiles, in each of which the bitstream is restricted to a single	to mark a bitstream as to what of the many independent coding tools are exercis
	IDR picture. EVC facilitates certain walled-garden implementations under commer	ed in the bitstream, in a spirit similar to the general_constraint_info of <xref
	cial constraints imposed by intellectual property rights by including syntax ele	target="VVC"/>.</t>
	ments that allow encoders to mark a bitstream as to what of the many independent	<t>Conceptually, all EVC, AVC, HEVC, and VVC include a Video Coding Laye
	coding tools are exercised in the bitstream, in a spirit similar to the general	r (VCL), a term that is often used to refer to the coding-tool features, and a N
	_constraint_flags of <xref target="VVC"/>.</t>	etwork Abstraction Layer (NAL), which usually refers to the systems and transpor
		t interface aspects of the codecs.</t>
	<t>Conceptually, all EVC, AVC, HEVC and VVC include a Video Coding Layer (VCL);	<section anchor="coding-tool-features-informative">
	a term that is often used to refer to the coding-tool features, and a Network Ab	<name>Coding-Tool Features (Informative)</name>
	straction Layer (NAL), which usually refers to the systems and transport interfa
	ce aspects of the codecs.</t>

	<section anchor="coding-tool-features-informative"><name>Coding-Tool Features (i
	nformative)</name>

	<t>Coding blocks and transform structure</t>

	<t>EVC uses a traditional block-based coding structure, which divides the encode
	d image into blocks of up to 64x64 luma samples for the Baseline profile and 128
	x128 luma samples for the Main profile that can be recursively divided into smal
	ler blocks. The baseline profiles utilize an HEVC-like quad-tree blocks partitio
	ning that allows to divide a block horizontally and vertically onto four smaller
	square blocks. The Main profile adds two advanced coding structure tools: 1) Bi
	nary Ternary Tree (BTT) partitioning that allows non-square coding units; and 2)
	Split Unit Coding Order segmentation that changes the processing order of the b
	locks from traditional left-to-right and top-to-bottom scanning order processing
	to an alternative right-to-left and bottom-to-top scanning order. In the Main p
	rofile, the picture can be divided into slices and tiles, which can be independe
	ntly encoded and/or decoded in parallel.</t>

	<t>EVC also uses a traditional video codecs prediction model assuming two genera
	l types of predictions: Intra (spatial) and Inter (temporal) predictions. A resi
	due block is calculated by subtracting predicted data from the original (encoded
	) one. The Baseline profile allows only discrete cosine transform (DCT-2) and sc
	alar quantization to transform and quantize residue data, wherein the Main profi
	le additionally has options to use discrete sine transform (DST-7) and another t
	ype of discrete cosine transform (DCT-8). In addition, for the Main profile, Imp
	roved Quantization and Transform (IQT) uses a different mapping/clipping functio
	n for quantization. An inverse zig-zag scanning order is used for coefficient co
	ding. Advanced Coefficient Coding (ADCC) in the Main profile can code coefficien
	t values more efficiently, for example, indicated by the last non-zero coefficie
	nt. The Baseline profile uses a straightforward run-length encoding (RLE) based
	approach to encode the quantized coefficients.</t>

	<t>Entropy coding</t>

	<t>EVC uses a similar binary arithmetic coding mechanism as HEVC CABAC and VVC.
	The mechanism includes a binarization step and a probability update defined by a
	lookup table. In the Main profile, the derivation process of syntax elements ba
	sed on adjacent blocks makes the context modeling and initialization process mor
	e efficient.</t>

	<t>In-loop filtering</t>

	<t>The Baseline profile of EVC uses the deblocking filter defined in H.263 Annex
	J. In the Main profile, an Advanced Deblocking Filter (ADDB) can be used as an
	alternative, which can further reduce undesirable compression artifacts. The Mai
	n profile also defines two additional in-loop filters that can be used to improv
	e the quality of decoded pictures before output and/or for inter-prediction. A H
	adamard Transform Domain Filter (HTDF) is applied to the luma samples before deb
	locking, and a lookup table is used to determine four adjacent samples for filt
	ering. An adaptive Loop Filter (ALF) allows to send signals of up to 25 differen
	t filters for the luma components, and the best filter can be selected through t
	he classification process for each 4x4 block. Similarly to VVC, the filter param
	eters of ALF are signaled in the Adaptation Parameter Set (APS).</t>

	<t>Inter-prediction</t>

	<t>The basis of EVC's inter-prediction is motion compensation using interpol
	ation filters with a quarter sample resolution. In the Baseline profile, a motio
	n vector is transmitted using one of three spatially neighboring motion vectors
	and a temporally collocated motion vector as a predictor. A motion vector differ
	ence may be signaled relative to the selected predictor, but there is a case whe
	re no motion vector difference is signaled, and there is no remaining data in th
	e block. This mode is called a skip mode. The Main profile includes six addition
	al tools to provide improved inter-prediction. With Advanced Motion Vectors Pred
	iction (ADMVP), adjacent blocks can be conceptually merged to indicate that they
	use the same motion, but more advanced schemes can also be used to create predi
	ctions from the basic model list of candidate predictors. The Merge with Motion
	Vector Difference (MMVD) tool uses a process similar to the concept of merging n
	eighboring blocks but also allows the use of expressions that include a starting
	point, motion amplitude, and direction of motion to send a motion vector signal
	. Using Advanced Motion Vector Prediction (AMVP), candidate motion vector predic
	tions for the block can be derived from its neighboring blocks in the same pictu
	re and collocated blocks in the reference picture. The Adaptive Motion Vector Re
	solution (AMVR) tool provides a way to reduce the accuracy of a motion vector fr
	om a quarter sample to half sample, full sample, double sample, or quad sample,
	which provides an efficiency advantage, such as when sending large motion vector
	differences. The Main profile also includes the Decoder-side Motion Vector Refi
	nement (DMVR), which uses a bilateral template matching process to refine the mo
	tion vectors without additional signaling.</t>

	<t>Intra prediction and intra-coding</t>

	<t>Intra prediction in EVC is performed on adjacent samples of coding units in a
	partitioned structure. For the Baseline profile, when all coding units are squa
	re, there are five different prediction modes: DC (mean value of the neighborhoo
	d), horizontal, vertical, and two different diagonal directions. In the Main pro
	file, intra prediction can be applied to any rectangular coding unit, and 28 add
	itional direction modes are available in the so-called Enhanced Intra Prediction
	Directions (EIPD). In the Main profile, an encoder can also use Intra Block Cop
	y (IBC), where previously decoded sample blocks of the same picture are used as
	a predictor. A displacement vector in integer sample precision is signaled to in
	dicate where the prediction block in the current picture is used for this mode.<
	/t>

	<t>Reference frames management</t>

	<t>In EVC, decoded pictures can be stored in a decoded picture buffer (DPB) for
	predicting pictures that follow them in the decoding order. In the Baseline prof
	ile, the management of the DPB (i.e., the process of adding and deleting referen
	ce pictures) is controlled by a straightforward AVC-like sliding window approach
	with very few parameters from the SPS. For the Main profile, DPB management can
	be handled much more flexibly using explicitly signaled reference Picture Lists
	(RPL) in the SPS or slice level.</t>

	</section>
	<section anchor="systems-and-transport-interfaces"><name>Systems and Transport I
	nterfaces</name>

	<t>EVC inherits the basic systems and transport interface designs from AVC and H
	EVC. These include the NAL-unit-based syntax, hierarchical syntax and data unit
	structure, and Supplemental Enhancement Information (SEI) message mechanism. The
	hierarchical syntax and data unit structure consists of a sequence-level parame
	ter set (SPS), two picture-level parameter sets (PPS and APS, each of which can
	apply to one or more pictures), slice-level header parameters, and lower-level p
	arameters.</t>

	<t>A number of key components that influenced the Network Abstraction Layer desi
	gn of EVC as well as this document, are described below:</t>

	<t>Sequence parameter set</t>


	<ul empty="true"><li>	<dl newline="true">
	<t>The Sequence Parameter Set (SPS) contains syntax elements pertaining to a C	<dt>Coding blocks and transform structure</dt>
	oded Video Sequence (CVS), which is a group of pictures, starting with a random	<dd><t>EVC uses a traditional block-based coding structure, which
	access point picture and followed by zero or more pictures that may depend on ea	divides the encoded image into blocks of up to 64x64 luma samples
	ch other and the random access point picture. In MPEG-2, the equivalent of a CVS	for the Baseline profile and 128x128 luma samples for the Main
	is a Group of Pictures (GOP), which generally started with an I frame and is fo	profile that can be recursively divided into smaller blocks. The
	llowed by P and B frames. While more complex in its options of random access poi	Baseline profiles utilize HEVC-like quad-tree-blocks partitioning
	nts, EVC retains this basic concept. In many TV-like applications, a CVS contain	that allows a block to be divided horizontally and vertically into
	s a few hundred milliseconds to a few seconds of video. In video conferencing (w	four smaller square blocks. The Main profile adds two advanced
	ithout switching MCUs involved), a CVS can be as long in duration as the whole s	coding structure tools: 1) Binary Ternary Tree (BTT) partitioning
	ession.</t>	that allows non-square coding units and 2) Split Unit Coding Order
	</li></ul>	segmentation that changes the processing order of the blocks from
		traditional left-to-right and top-to-bottom scanning order
		processing to an alternative right-to-left and bottom-to-top
		scanning order. In the Main profile, the picture can be divided into
		slices and tiles, which can be independently encoded and/or decoded
		in parallel.</t>
		<t>EVC also uses a traditional video codecs prediction model assuming
		two general types of predictions: Intra (spatial) and Inter (temporal) predictio
		ns. A residue block is calculated by subtracting predicted data from the origina
		l (encoded) one. The Baseline profile allows only discrete cosine transform (DCT
		-2) and scalar quantization to transform and quantize residue data, wherein the
		Main profile additionally has options to use discrete sine transform (DST-7) and
		another type of discrete cosine transform (DCT-8). In addition, for the Main pr
		ofile, Improved Quantization and Transform (IQT) uses a different mapping or cli
		pping function for quantization. An inverse zig-zag scanning order is used for c
		oefficient coding. Advanced Coefficient Coding (ADCC) in the Main profile can co
		de coefficient values more efficiently, for example, indicated by the last non-z
		ero coefficient. The Baseline profile uses a straightforward RLE-based approach
		to encode the quantized coefficients.</t></dd>
		<dt>Entropy coding</dt>
		<dd><t>EVC uses a similar binary arithmetic coding mechanism as HEVC C
		ABAC (context adaptive binary arithmetic coding) and VVC. The mechanism includes
		a binarization step and a probability update defined by a lookup table. In the
		Main profile, the derivation process of syntax elements based on adjacent blocks
		makes the context modeling and initialization process more efficient.</t>
		</dd>


	<t>Picture and adaptation parameter set</t>	<dt>In-loop filtering</dt>
		<dd><t>The Baseline profile of EVC uses the deblocking filter defined
		in H.263 Annex J <xref target="VIDEO-CODING" format="default"/>. In the Main pro
		file, an Advanced Deblocking Filter (ADDB) can be used as an alternative, which
		can further reduce undesirable compression artifacts. The Main profile also defi
		nes two additional in-loop filters that can be used to improve the quality of de
		coded pictures before output and/or for Inter prediction. A Hadamard Transform D
		omain Filter (HTDF) is applied to the luma samples before deblocking, and a look
		up table is used to determine four adjacent samples for filtering. An adaptive
		Loop Filter (ALF) allows signals of up to 25 different filters to be sent for th
		e luma components; the best filter can be selected through the classification pr
		ocess for each 4x4 block. Similarly to VVC, the filter parameters of ALF are sig
		naled in the Adaptation Parameter Set (APS).</t></dd>


	<ul empty="true"><li>	<dt>Inter prediction</dt>
	<t>The Picture Parameter Set and the Adaptation Parameter Set (PPS and APS, re	<dd><t>The basis of EVC's Inter prediction is motion compensation usin
	spectively) carry information pertaining to a single picture. The PPS contains i	g interpolation filters with a quarter sample resolution. In the Baseline profil
	nformation that is likely to stay constant from picture to picture, at least for	e, a motion vector is transmitted using one of three spatially neighboring motio
	pictures of a certain type whereas the APS contains information, such as adapti	n vectors and a temporally collocated motion vector as a predictor. A motion vec
	ve loop filter coefficients, that are likely to change from picture to picture.<	tor difference may be signaled relative to the selected predictor, but there is
	/t>	a case where no motion vector difference is signaled, and there is no remaining
	</li></ul>	data in the block. This mode is called a "skip" mode. The Main profile includes
		six additional tools to provide improved Inter prediction. With Advanced Motion
		Vectors Prediction (ADMVP), adjacent blocks can be conceptually merged to indica
		te that they use the same motion, but more advanced schemes can also be used to
		create predictions from the basic model list of candidate predictors. The Merge
		with Motion Vector Difference (MMVD) tool uses a process similar to the concept
		of merging neighboring blocks but also allows the use of expressions that includ
		e a starting point, motion amplitude, and direction of motion to send a motion v
		ector signal. Using Advanced Motion Vector Prediction (AMVP), candidate motion v
		ector predictions for the block can be derived from its neighboring blocks in th
		e same picture and collocated blocks in the reference picture. The Adaptive Moti
		on Vector Resolution (AMVR) tool provides a way to reduce the accuracy of a moti
		on vector from a quarter sample to half sample, full sample, double sample, or q
		uad sample, which provides an efficiency advantage, such as when sending large m
		otion vector differences. The Main profile also includes the Decoder-side Motion
		Vector Refinement (DMVR), which uses a bilateral template matching process to r
		efine the motion vectors without additional signaling.</t></dd>


	<t>Profile, level, and toolsets</t>	<dt>Intra prediction and intra coding</dt>
		<dd><t>Intra prediction in EVC is performed on adjacent samples of cod
		ing units in a partitioned structure. For the Baseline profile, when all coding
		units are square, there are five different prediction modes: DC (mean value of t
		he neighborhood), horizontal, vertical, and two different diagonal directions. I
		n the Main profile, intra prediction can be applied to any rectangular coding un
		it, and 28 additional direction modes are available in the Enhanced Intra Predic
		tion Directions (EIPDs). In the Main profile, an encoder can also use Intra Bloc
		k Copy (IBC), where previously decoded sample blocks of the same picture are use
		d as a predictor. A displacement vector in integer sample precision is signaled
		to indicate where the prediction block in the current picture is used for this m
		ode.</t></dd>


	<ul empty="true"><li>	<dt>Reference frames management</dt>
	<t>Profiles and levels follow the same design considerations known from AVC, H	<dd><t>In EVC, decoded pictures can be stored in a decoded picture buf
	EVC, and video codecs as old as MPEG-1 Video. The profile defines a set of tools	fer (DPB) for predicting pictures that follow them in the decoding order. In the
	(not to confuse with the "toolset" discussed below) that a decoder co	Baseline profile, the management of the DPB (i.e., the process of adding and de
	mpliant with this profile has to support. In EVC, profiles are defined in Annex	leting reference pictures) is controlled by a straightforward AVC-like sliding w
	A. Formally, they are defined as a set of constraints that a bitstream needs to	indow approach with very few parameters from the sequence parameter set (SPS). F
	conform to. In EVC, the Baseline profile is much more severely constraint than	or the Main profile, DPB management can be handled much more flexibly using expl
	the Main profile, reducing implementation complexity. Levels relate to bitstream	icitly signaled Reference Picture Lists (RPLs) in the SPS or slice level.</t></d
	complexity in dimensions such as maximum sample decoding rate, maximum picture	d>
	size, and similar parameters directly related to computational complexity and/or	</dl>
	memory demands.</t>	</section>
	</li></ul>	<section anchor="systems-and-transport-interfaces">
		<name>Systems and Transport Interfaces</name>
		<t>EVC inherits the basic systems and transport interface designs from
		AVC and HEVC. These include the NAL-unit-based syntax, hierarchical syntax and
		data unit structure, and Supplemental Enhancement Information (SEI) message mech
		anism. The hierarchical syntax and data unit structure consists of a sequence-le
		vel parameter set (i.e., SPS), two picture-level parameter sets (i.e., PPS and A
		PS, each of which can apply to one or more pictures), slice-level header paramet
		ers, and lower-level parameters.</t>
		<t>A number of key components that influenced the NAL design of EVC as
		well as this document are described below:</t>


		<dl newline="true">
		<dt>Sequence parameter set</dt>
		<dd><t>The Sequence Parameter Set (SPS) contains syntax elements p
		ertaining to a Coded Video Sequence (CVS), which is a group of pictures, startin
		g with a random access point picture and followed by zero or more pictures that
		may depend on each other and the random access point picture. In MPEG-2, the equ
		ivalent of a CVS is a Group of Pictures (GOP), which generally starts with an I
		frame and is followed by P and B frames. While more complex in its options of ra
		ndom access points, EVC retains this basic concept. In many TV-like applications
		, a CVS contains a few hundred milliseconds to a few seconds of video. In video
		conferencing (without switching Multipoint Control Units (MCUs) involved), a CVS
		can be as long in duration as the whole session.</t></dd>
		<dt>Picture and adaptation parameter set</dt>
		<dd><t>The Picture Parameter Set (PPS) and the Adaptation Paramete
		r Set (APS) carry information pertaining to a single picture. The PPS contains i
		nformation that is likely to stay constant from picture to picture, at least for
		pictures of a certain type; whereas the APS contains information, such as adapt
		ive loop filter coefficients, that are likely to change from picture to picture.
		</t></dd>
		<dt>Profile, level, and toolsets</dt>
		<dd><t>Profiles and levels follow the same design considerations k
		nown from AVC, HEVC, and video codecs as old as MPEG-1 Video. The profile define
		s a set of tools (not to be confused with the "toolset" discussed below) that a
		decoder compliant with this profile has to support. In EVC, profiles are defined
		in Annex A of <xref target="EVC"/>. Formally, they are defined as a set of con
		straints that a bitstream needs to conform to. In EVC, the Baseline profile is m
		uch more severely constrained than the Main profile, reducing implementation com
		plexity. Levels relate to bitstream complexity in dimensions such as maximum sam
		ple decoding rate, maximum picture size, and similar parameters directly related
		to computational complexity and/or memory demands.</t>
	<t>Profiles and levels are signaled in the highest parameter set available, the SPS.</t>	<t>Profiles and levels are signaled in the highest parameter set available, the SPS.</t>

		<t>EVC contains another mechanism related to the use of coding tools, known as the toolset syntax elements. These syntax elements, toolset_idc_h and toolset_i dc_l (located in the SPS), are bitmasks that allow encoders to indicate which co ding tools they are using within the menu of profiles offered by the profile tha t is also signaled. No decoder conformance point is associated with the toolset, but a bitstream that was using a coding tool that is indicated as not being use d in the toolset syntax element would be non-compliant. While MPEG specifically rules out the use of the toolset syntax element as a conformance point, walled g arden implementations could do so without incurring the interoperability problem s MPEG fears and create bitstreams and decoders that do not support one or more given tools. That, in turn, may be useful to mitigate certain intellectual prope rty-related risks.</t> </dd>


	<ul empty="true"><li>	<dt>Bitstream and elementary stream</dt>
	<t>EVC contains another mechanism related to the use of coding tools, known as	<dd><t>Above the Coded Video Sequence (CVS), EVC defines a video bitst
	the toolset syntax element. This syntax element, toolset_idc_h and toolset_idc_	ream that can be used as an elementary stream in the MPEG systems context. For t
	l located in the SPS, is a bitmask that allows encoders to indicate which coding	his document, the video bitstream syntax level is not relevant.</t></dd>
	tools they are using within the menu of profiles offered by the profile that is	<dt>Random access support</dt>
	also signaled. No decoder conformance point is associated with the toolset, but	<dd><t>EVC supports random access mechanisms based on IDR and clean ra
	a bitstream that was using a coding tool that is indicated as not being used in	ndom access (CRA) access units.</t></dd>
	the toolset syntax element would be non-compliant. While MPEG specifically rule	<dt>Temporal scalability support</dt>
	s out the use of the toolset syntax element as a conformance point, walled garde	<dd><t>EVC supports temporal scalability through the generalized refer
	n implementations could do so without incurring the interoperability problems MP	ence picture selection approach known since AVC/SVC. Up to six temporal layers a
	EG fears and create bitstreams and decoders that do not support one or more give	re supported. The temporal layer is signaled in the NAL unit header (which co-se
	n tools. That, in turn, may be useful to mitigate certain intellectual property-	rves as the payload header in this document), in the nuh_temporal_id field.</t><
	related risks.</t>	/dd>
	</li></ul>

	<t>Bitstream and elementary stream</t>

	<ul empty="true"><li>
	<t>Above the Coded Video Sequence (CVS), EVC defines a video bitstream that ca
	n be used as an elementary stream in the MPEG systems context. For this document
	, the video bitstream syntax level is not relevant.</t>
	</li></ul>

	<t>Random access support</t>

	<ul empty="true"><li>
	<t>EVC supports random access mechanisms based on IDR and CRA access units.</t
	>
	</li></ul>

	<t>Temporal scalability support</t>

	<ul empty="true"><li>
	<t>EVC supports temporal scalability through the generalized reference picture
	selection approach known since AVC/SVC. Up to six temporal layers are supported
	. The temporal layer is signaled in the NAL unit header (which co-serves as the
	payload header in this document), in the nuh_temporal_id field.</t>
	</li></ul>

	<t>Reference picture management</t>

	<ul empty="true"><li>
	<t>EVC's reference picture management is POC-based (Picture Order Count),
	similar to HEVC. In the Main profile, substantially all reference picture list m
	anipulations available in HEVC are available, including explicit transmissions/u
	pdates of reference picture lists, although for reference pictures management pu
	rposes, EVC uses a modern VVC-like RPL approach, which is conceptually simpler t
	han the HEVC one. In the Baseline profile, reference picture management is more
	restricted, allowing for a comparatively simple group of picture structures only
	.</t>
	</li></ul>

	<t>SEI Message</t>

	<ul empty="true"><li>
	<t>EVC inherits many of HEVC's SEI Messages, occasionally with syntax and/
	or semantics changes, making them applicable to EVC. In addition, some of the co
	dec-agnostic SEI Messages of the VSEI specification are also mapped.</t>
	</li></ul>

	</section>
	<section anchor="parallel-processing-support-informative"><name>Parallel Process
	ing Support (informative)</name>

	<ul empty="true"><li>
	<t>EVC's Baseline profile includes no tools specifically addressing parall
	el processing support. The Main profile includes independently decodable slices
	for parallel processing. The slices are defined as any rectangular region within
	a picture and can be encoded to have no coding dependencies with other slices i
	n the same picture but with other slices from the previous picture. No specific
	support for parallel processing is specified in this RTP payload format.</t>
	</li></ul>


	</section>	<dt>Reference picture management</dt>
	<section anchor="NALUnitHeader"><name>NAL Unit Header</name>	<dd><t>EVC's reference picture management is POC-based, similar to HEV
		C. In the Main profile, substantially all reference picture list manipulations a
		vailable in HEVC are specified, including explicit transmissions or updates of r
		eference picture lists. Although for reference pictures management purposes, EVC
		uses a modern VVC-like RPL approach, which is conceptually simpler than the HEV
		C one. In the Baseline profile, reference picture management is more restricted,
		allowing for a comparatively simple group of picture structures only.</t></dd>
		<dt>SEI Message</dt>
		<dd><t>EVC inherits many of HEVC's SEI messages, occasionally with syn
		tax and/or semantics changes, making them applicable to EVC.
		In addition, some of the codec-agnostic SEI messages of the VSEI specification <
		xref target="VSEI"/> are also mapped.</t></dd>
		</dl>
		</section>
		<section anchor="parallel-processing-support-informative">
		<name>Parallel Processing Support (Informative)</name>


	<t>EVC maintains the NAL unit concept of <xref target="VVC"/> with different par	<t>EVC's Baseline profile includes no tools specifically addressing
	ameter options. EVC also uses a two-byte NAL unit header, as shown in <xref targ	parallel-processing support. The Main profile includes independently
	et="evc-nuh"/>. The payload of a NAL unit refers to the NAL unit excluding the	decodable slices for parallel processing. The slices are defined as
	NAL unit header.</t>	any rectangular region within a picture. They can be encoded to have
		coding dependencies with other slices from the previous picture but
		not with other slices in the same picture. No specific support for
		parallel processing is specified in this RTP payload format.</t>


	<figure anchor="evc-nuh"><artwork><![CDATA[	</section>
		<section anchor="NALUnitHeader">
		<name>NAL Unit Header</name>
		<t>EVC maintains the NAL unit concept of <xref target="VVC"/> with dif
		ferent parameter options. EVC also uses a two-byte NAL unit header, as shown in
		<xref target="evc-nuh"/>. The payload of a NAL unit refers to the NAL unit excl
		uding the NAL unit header.</t>
		<figure anchor="evc-nuh">
		<name>The Structure of the EVC NAL Unit Header</name>
		<artwork><![CDATA[
	0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7	0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\|F\| Type \| TID \| Reserve \|E\|	\|F\| Type \| TID \| Reserve \|E\|

	+-------------+-----------------+	+-------------+-----------------+]]></artwork>
		</figure>
	The Structure of the EVC NAL Unit Header	<t>The semantics of the fields in the NAL unit header are as specified
	]]></artwork></figure>	in EVC and described briefly below for convenience. In addition to the name and
		size of each field, the corresponding syntax element name in EVC is also provid
	<t>The semantics of the fields in the NAL unit header are as specified in EVC an	ed.</t>
	d described briefly below for convenience. In addition to the name and size of e
	ach field, the corresponding syntax element name in EVC is also provided.</t>

	<t>F: 1 bit</t>

	<ul empty="true"><li>
	<t>forbidden_zero_bit. Required to be zero in EVC. Note that the inclusion of
	this bit in the NAL unit header was included to enable transport of EVC video o
	ver MPEG-2 transport systems (avoidance of start code emulations) <xref target="
	MPEG2S"/>. In this document, the value 1 may be used to indicate a syntax violat
	ion, e.g., for a NAL unit resulting from aggregating a number of fragmented unit
	s of a NAL unit but missing the last fragment, as described in <xref target="fun
	its"/>.</t>
	</li></ul>

	<t>Type: 6 bits</t>

	<ul empty="true"><li>
	<t>nal_unit_type_plus1. This field allows the NAL Unit Type to be computed. Th
	e NAL Unit Type (NalUnitType) is equal to the value found in this field, minus 1
	; in other words:</t>
	</li></ul>

	<ul empty="true"><li>
	<ul empty="true"><li>
	<t>NalUnitType = nal_unit_type_plus1 - 1.</t>
	</li></ul>
	</li></ul>

	<ul empty="true"><li>
	<t>The NAL unit type is detailed in Table 4 of <xref target="EVC"/>. If the va
	lue of NalUnitType is less than or equal to 23, the NAL unit is a VCL NAL unit.
	Otherwise, the NAL unit is a non-VCL NAL unit. For a reference of all currentl
	y defined NAL unit types and their semantics, please refer to Section 7.4.2.2 in
	<xref target="EVC"/>. Note that nal_unit_type_plus1 MUST NOT be zero.</t>
	</li></ul>

	<t>TID: 3 bits</t>

	<ul empty="true"><li>
	<t>nuh_temporal_id. This field specifies the temporal identifier of the NAL u
	nit. The value of TemporalId is equal to TID. TemporalId shall be equal to 0 if
	it is an IDR NAL unit type (NAL unit type 1).</t>
	</li></ul>

	<t>Reserve: 5 bits</t>

	<ul empty="true"><li>
	<t>nuh_reserved_zero_5bits. This field shall be equal to the version of the EV
	C standard. Values of nuh_reserved_zero_5bits greater than 0 are reserved for fu
	ture use by ISO/IEC. Decoders conforming to a profile specified in <xref target=
	"EVC"/>'s Annex A shall ignore (i.e., remove from the bitstream and discard)
	all NAL units with values of nuh_reserved_zero_5bits greater than 0.</t>
	</li></ul>

	<t>E: 1 bit</t>

	<ul empty="true"><li>
	<t>nuh_extension_flag. This field shall be equal to the version of the EVC sta
	ndard. The value of nuh_extension_flag equal to 1 is reserved for future use by
	ISO/IEC. Decoders conforming to a profile specified in <xref target="EVC"/>'
	s Annex A shall ignore (i.e., remove from the bitstream and discard) all NAL uni
	ts with values of nuh_extension_flag equal to 1.</t>
	</li></ul>

	</section>
	</section>
	<section anchor="overview-of-the-payload-format"><name>Overview of the Payload F
	ormat</name>

	<t>This payload format defines the following processes required for transport of
	EVC-coded data over RTP <xref target="RFC3550"/>:</t>

	<t><list style="symbols">
	<t>usage of RTP header with this payload format</t>
	<t>packetization of EVC-coded NAL units into RTP packets using
	three types of payload structures: a single NAL unit,
	aggregation, and fragment unit</t>
	<t>transmission of EVC NAL units of the same bitstream within a
	single RTP stream.</t>
	<t>media type parameters to be used with the Session Description
	Protocol (SDP) <xref target="RFC8866"/></t>
	<t>usage of RTCP feedback messages</t>
	</list></t>

	</section>
	</section>
	<section anchor="conventions"><name>Conventions</name>

	<t>The key words "MUST", "MUST NOT", "REQUIRED", &
	quot;SHALL", "SHALL
	NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",
	"NOT RECOMMENDED",
	"MAY", and "OPTIONAL" in this document are to be interpreted
	as
	described in BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and
	only when, they
	appear in all capitals, as shown above.</t>


	</section>	<dl>
	<section anchor="definitionsandabbr"><name>Definitions and Abbreviations</name>	<dt>F:</dt>
		<dd><t>1 bit</t>
		<dl>
		<dt>forbidden_zero_bit:</dt>
		<dd>Required to be zero in EVC. Note that the
		inclusion of this bit in the NAL unit header was included to
		enable transport of EVC video over MPEG-2 transport systems
		(avoidance of start code emulations) <xref target="MPEG2S"/>. In
		this document, the value 1 may be used to indicate a syntax
		violation, e.g., for a NAL unit resulting from aggregating a
		number of fragmented units of a NAL unit but missing the last
		fragment, as described in <xref target="funits"/>.</dd></dl>
		</dd>
		<dt>Type:</dt>
		<dd>
		<t>6 bits</t>
		<dl>
		<dt>nal_unit_type_plus1:</dt>
		<dd><t>This field allows the NAL Unit Type to
		be computed. The NAL Unit Type (NalUnitType) is equal to the
		value found in this field, minus 1; in other words:</t>
		<t>NalUnitType = nal_unit_type_plus1 - 1.</t>
		<t>The NAL unit type is detailed in Table 4 of <xref
		target="EVC"/>. If the value of NalUnitType is less than or
		equal to 23, the NAL unit is a VCL NAL unit. Otherwise, the NAL
		unit is a non-VCL NAL unit. For a reference of all currently
		defined NAL unit types and their semantics, please refer to
		Section 7.4.2.2 of <xref target="EVC"/>. Note that
		nal_unit_type_plus1 <bcp14>MUST NOT</bcp14> be zero.</t></dd></dl>
		</dd>
		<dt>TID:</dt>
		<dd><t>3 bits</t>
		<dl>
		<dt>nuh_temporal_id:</dt>
		<dd>This field specifies the temporal identifier
		of the NAL unit. The value of TemporalId is equal to
		TID. TemporalId shall be equal to 0 if it is an IDR NAL unit type
		(NAL unit type 1).</dd></dl>
		</dd>
		<dt>Reserve:</dt>
		<dd><t>5 bits</t>
		<dl>
		<dt>nuh_reserved_zero_5bits:</dt>
		<dd>This field shall be equal to the version of the EVC
		standard. Values of nuh_reserved_zero_5bits greater than 0 are
		reserved for future use by ISO/IEC. Decoders conforming to a
		profile specified in Annex A of <xref target="EVC"/> shall ignore
		(i.e., remove from the bitstream and discard) all NAL units with
		values of nuh_reserved_zero_5bits greater than 0.</dd></dl>
		</dd>
		<dt>E:</dt>
		<dd><t>1 bit</t>
		<dl>
		<dt>nuh_extension_flag:</dt>
		<dd>This field shall be equal to the version of
		the EVC standard. The value of nuh_extension_flag equal to 1 is
		reserved for future use by ISO/IEC. Decoders conforming to a
		profile specified in Annex A of <xref target="EVC"/> shall ignore
		(i.e., remove from the bitstream and discard) all NAL units with
		values of nuh_extension_flag equal to 1.</dd></dl>
		</dd>
		</dl>
		</section>
		</section>
		<section anchor="overview-of-the-payload-format">
		<name>Overview of the Payload Format</name>
		<t>This payload format defines the following processes required for tran
		sport of EVC-coded data over RTP <xref target="RFC3550"/>:</t>
		<ul spacing="normal">
		<li>usage of RTP header with this payload format</li>
		<li>packetization of EVC-coded NAL units into RTP packets using
		three types of payload structures: a single NAL unit, aggregation,
		and fragment unit</li>
		<li>transmission of EVC NAL units of the same bitstream within a
		single RTP stream</li>
		<li>usage of media type parameters to be used with the Session
		Description Protocol (SDP) <xref target="RFC8866"/></li>
		<li>usage of RTCP feedback messages</li>
		</ul>
		</section>
		</section>
		<section anchor="conventions">
		<name>Conventions</name>
		<t>
		The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
		"<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>
		",
		"<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
		"<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
		"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to
		be
		interpreted as described in BCP 14 <xref target="RFC2119"/> <xref
		target="RFC8174"/> when, and only when, they appear in all capitals, as
		shown here.
		</t>


	<section anchor="definitions"><name>Definitions</name>	</section>
	<t>This document uses the terms and definitions of EVC. <xref target="definitio	<section anchor="definitionsandabbr">
	nforevc"/>	<name>Definitions and Abbreviations</name>
		<section anchor="definitions">
		<name>Definitions</name>
		<t>This document uses the terms and definitions of EVC. <xref target="d
		efinitionforevc"/>
	lists relevant definitions from <xref target="EVC"/> for convenience. <xref tar get="def"/>	lists relevant definitions from <xref target="EVC"/> for convenience. <xref tar get="def"/>
	provides definitions specific to this document.</t>	provides definitions specific to this document.</t>

		<section anchor="definitionforevc">
		<name>Definitions from the EVC Standard</name>
		<dl spacing="normal" newline="true">
		<dt>Access Unit (AU):</dt>
		<dd>A set of NAL units that are associated with each other
		according to a specified classification rule, are consecutive in
		decoding order, and contain exactly one coded picture.</dd>
		<dt>Adaptation Parameter Set (APS):</dt>
		<dd>A syntax structure containing syntax elements that apply to
		zero or more slices as determined by zero or more syntax elements
		found in slice headers.</dd>
		<dt>Bitstream:</dt>
		<dd>A sequence of bits, in the form of a NAL unit stream or a byte
		stream, that forms the representation of coded pictures and
		associated data forming one or more CVSs.</dd>
		<dt>Coded Picture:</dt>
		<dd>A coded representation of a picture containing all CTUs of the
		picture.</dd>
		<dt>Coded Video Sequence (CVS):</dt>
		<dd>A sequence of access units that consists, in decoding order,
		of an IDR access unit, followed by zero or more access units that
		are not IDR access units, including all subsequent access units up
		to but not including any subsequent access unit that is an IDR
		access unit.</dd>
		<dt>Coding Tree Block (CTB):</dt>
		<dd>An NxN block of samples for some value of N such that the
		division of a component into CTBs is a partitioning.</dd>
		<dt>Coding Tree Unit (CTU):</dt>


	<section anchor="definitionforevc"><name>Definitions from the EVC Standard</name	<dd>A CTB of luma samples, two corresponding CTBs of chroma
	>	samples of a picture that has three sample arrays, or a CTB of
		samples of a monochrome picture or a picture that is coded using
	<t>Access Unit: A set of NAL units that are associated with each other according	three separate color planes and syntax structures used to code
	to a specified classification rule, are consecutive in decoding order, and cont	the samples.</dd>
	ain exactly one coded picture.</t>	<dt>Decoded Picture:</dt>
		<dd>A decoded picture is derived by decoding a coded picture.</dd>
	<t>Adaptation parameter set (APS): A syntax structure containing syntax	<dt>Decoded Picture Buffer (DPB):</dt>
	elements that apply to zero or more slices as determined by zero or	<dd>A buffer holding decoded pictures for reference, output
	more syntax elements found in slice headers.</t>	reordering, or output delay specified for the hypothetical
		reference decoder in Annex C of the <xref target="EVC"/>
	<t>Bitstream: A sequence of bits, in the form of a NAL unit stream or a byte str	standard.</dd>
	eam, that forms the representation	<dt>Dynamic Range Adjustment (DRA):</dt>
	of coded pictures and associated data forming one or more coded video sequences	<dd>A mapping process that is applied to the decoded picture prior to
	(CVSs).</t>	cropping and output as part of the decoding process; it is
		controlled by parameters conveyed in an Adaptation Parameter Set
	<t>Coded Picture: A coded representation of a picture containing all CTUs of the	(APS).</dd>
	picture.</t>	<dt>Hypothetical Reference Decoder (HRD):</dt>
		<dd>A hypothetical decoder model that specifies constraints on the
	<t>Coded Video Sequence (CVS): A sequence of access units that consists, in deco	variability of conforming NAL unit streams or conforming byte
	ding order, of an IDR access unit, followed by zero or more access units that ar	streams that an encoding process may produce.</dd>
	e not IDR access units, including all subsequent access units up to but not incl	<dt>IDR Access Unit:</dt>
	uding any subsequent access unit that is an IDR access unit.</t>	<dd>An access unit in which the coded picture is an IDR picture.</dd>
		<dt>IDR Picture:</dt>
	<t>Coding Tree Block (CTB): An NxN block of samples for some value of N such tha	<dd>The coded picture for which each VCL NAL unit has NalUnitType equ
	t the division of a component into CTBs is a partitioning.</t>	al to IDR_NUT.</dd>
		<dt>Level:</dt>
	<t>Coding Tree Unit (CTU): A CTB of luma samples, two corresponding CTBs of chro	<dd>A defined set of constraints on the values that may be taken
	ma samples of a picture that has three sample arrays, or a CTB of samples of a m	by the syntax elements and variables of this document, or the
	onochrome picture or a picture that is coded using three separate colour planes	value of a transform coefficient prior to scaling.</dd>
	and syntax structures used to code the samples.</t>	<dt>Network Abstraction Layer (NAL) Unit:</dt>
		<dd>A syntax structure containing an indication of the type of
	<t>Decoded Picture: A decoded picture is derived by decoding a coded picture.</t	data to follow and bytes containing that data in the form of an
	>	RBSP interspersed as necessary.</dd>
		<dt>Network Abstraction Layer (NAL) Unit Stream:</dt>
	<t>Decoded Picture Buffer (DPB): A buffer holding decoded pictures for reference	<dd>A sequence of NAL units.</dd>
	, output reordering, or output	<dt>Non-IDR Picture:</dt>
	delay specified for the hypothetical reference decoder in Annex C of <xref targe	<dd>A coded picture that is not an IDR picture.</dd>
	t="EVC"/> standard.</t>	<dt>Non-VCL NAL Unit:</dt>
		<dd>A NAL unit that is not a VCL NAL unit.</dd>
	<t>Dynamic Range Adjustment (DRA): A mapping process that is applied to decoded	<dt>Picture Parameter Set (PPS):</dt>
	picture prior to cropping and output as part of the decoding process and is con	<dd>A syntax structure containing syntax elements that apply to
	trolled by parameters conveyed in an Adaptation Parameter Set (APS).</t>	zero or more entire coded pictures as determined by a syntax
		element found in each slice header.</dd>
	<t>Hypothetical Reference Decoder (HRD): A hypothetical decoder model that speci	<dt>Picture Order Count (POC):</dt>
	fies constraints on the variability of conforming NAL unit streams or conforming	<dd>A variable that is associated with each picture, uniquely
	byte streams that an encoding process may produce.</t>	identifies the associated picture among all pictures in the CVS,
		and (when the associated picture is to be output from the DPB) indica
	<t>IDR access unit: access unit in which the coded picture is an IDR picture.</t	tes the position of the associated picture
	>	in output order relative to the output order positions of the
		other pictures in the same CVS that are to be output from the
	<t>IDR picture: coded picture for which each VCL NAL unit has NalUnitType equal	DPB.</dd>
	to IDR_NUT.</t>	<dt>Raw Byte Sequence Payload (RBSP):</dt>
		<dd>A syntax structure containing an integer number of bytes that
	<t>Level: A defined set of constraints on the values that may be taken by the sy	is encapsulated in a NAL unit and that is either empty or has the
	ntax elements and variables of this document, or the value of a transform coeffi	form of a string of data bits containing syntax elements followed
	cient prior to scaling.</t>	by an RBSP stop bit and zero or more subsequent bits equal to
		0.</dd>
	<t>Network Abstraction Layer (NAL) unit: A syntax structure containing an indica	<dt>Sequence Parameter Set (SPS):</dt>
	tion of the type of data to follow	<dd>A syntax structure containing syntax elements that apply to
	and bytes containing that data in the form of an RBSP interspersed as necessary.	zero or more entire CVSs as determined by the content of a syntax
	</t>	element found in the PPS referred to by a syntax element found in
		each slice header.</dd>
	<t>Network Abstraction Layer (NAL) Unit Stream: A sequence of NAL units.</t>	<dt>Slice:</dt>
		<dd>An integer number of tiles of a picture in the tile scan of
	<t>Non-IDR Picture: A coded picture that is not an IDR picture.</t>	the picture, exclusively contained in a single NAL unit.</dd>
		<dt>Tile:</dt>
	<t>Non-VCL NAL Unit: A NAL unit that is not a VCL NAL unit.</t>	<dd>A rectangular region of CTUs within a particular tile column and
		a particular tile row in a picture.</dd>
	<t>Picture Parameter Set (PPS): A syntax structure containing syntax elements th	<dt>Tile Column:</dt>
	at apply to zero or more entire coded pictures as determined by a syntax element	<dd>A rectangular region of CTUs having a height equal to the height
	found in each slice header.</t>	of the picture and width specified by syntax elements in the
		PPS.</dd>
	<t>Picture Order Count (POC): A variable that is associated with each picture, u	<dt>Tile Row:</dt>
	niquely identifies the associated picture among all pictures in the CVS, and, wh	<dd>A rectangular region of CTUs having a height specified by
	en the associated picture is to be output from the decoded picture buffer, indic	syntax elements in the PPS and a width equal to the width of the
	ates the position of the associated picture in output order relative to the outp	picture.</dd>
	ut order positions of the other pictures in the same CVS that are to be output f	<dt>Tile Scan:</dt>
	rom the decoded picture buffer.</t>	<dd>A specific sequential ordering of CTUs partitioning a picture
		in which the CTUs are ordered consecutively in CTU raster scan in
	<t>Raw Byte Sequence Payload (RBSP): A syntax structure containing an integer nu	a tile, whereas tiles in a picture are ordered consecutively in a
	mber of bytes that is encapsulated in a NAL unit and that is either empty or has	raster scan of the tiles of the picture.</dd>
	the form of a string of data bits containing syntax elements followed by an RBS	<dt>Video Coding Layer (VCL) NAL Unit:</dt>
	P stop bit and zero or more subsequent bits equal to 0.</t>	<dd>A collective term for coded slice NAL units and the subset of
		NAL units that have reserved values of NalUnitType that are
	<t>Sequence Parameter Set (SPS): A syntax structure containing syntax elements t	classified as VCL NAL units in this document.</dd>
	hat apply to zero or more entire CVSs as determined by the content of a syntax e	</dl>
	lement found in the PPS referred to by a syntax element found in each slice head	</section>
	er.</t>	<section anchor="def">
		<name>Definitions Specific to This Document</name>
	<t>Slice: integer number of tiles of a picture in the tile scan of the picture a	<dl newline="true" spacing="normal">
	nd that are exclusively contained in a single NAL unit.</t>	<dt>Media-Aware Network Element (MANE):</dt><dd><t>A network
		element, such as a middlebox, selective forwarding unit, or
	<t>Tile: rectangular region of CTUs within a particular tile column and a partic	application-layer gateway, that is capable of parsing certain
	ular tile row in a picture.</t>	aspects of the RTP payload headers or the RTP payload and reacting
		to their contents.</t>
	<t>Tile column: rectangular region of CTUs having a height equal to the height o	<aside><t>Informative note: The concept of a MANE goes beyond normal
	f the picture and width specified by syntax elements in the PPS.</t>	routers or gateways in that a MANE has to be aware of the
		signaling (e.g., to learn about the payload type mappings of the
	<t>Tile row: A rectangular region of CTUs having a height specified by syntax el	media streams), and in that it has to be trusted when working with
	ements in the PPS and a width equal to the width of the picture.</t>	Secure RTP (SRTP). The advantage of using MANEs is that they
		allow packets to be dropped according to the needs of the media
	<t>Tile scan: A specific sequential ordering of CTUs partitioning a picture in w	coding. For example, if a MANE has to drop packets due to
	hich the CTUs are ordered consecutively in CTU raster scan in a tile whereas til	congestion on a certain link, it can identify and remove those
	es in a picture are ordered consecutively in a raster scan of the tiles of the p	packets whose elimination produces the least adverse effect on the
	icture.</t>	user experience. After dropping packets, MANEs must rewrite RTCP
		packets to match the changes to the RTP stream, as specified in
	<t>Video coding layer (VCL) NAL unit: A collective term for coded slice NAL unit	<xref target="RFC3550" section="7" sectionFormat="of"/>.</t></aside>
	s and the subset of NAL units that have reserved values of NalUnitType that are	</dd>
	classified as VCL NAL units in this document.</t>	<dt>NAL unit decoding order:</dt><dd>A NAL unit order that conforms
		to the constraints on NAL unit order given in Section 7.4.2.3 of
	</section>	<xref target="EVC"/> and follows the order of NAL units in the
	<section anchor="def"><name>Definitions Specific to This Document</name>	bitstream.</dd>
		<dt>NALU-time:</dt><dd>The value that the RTP timestamp would have
	<t>Media-Aware Network Element (MANE): A network element, such as a	if the NAL unit would be transported in its own RTP packet.</dd>
	middlebox, selective forwarding unit, or application-layer gateway	<dt>NAL unit output order:</dt><dd>A NAL unit order in which NAL
	that is capable of parsing certain aspects of the RTP payload headers	units of different access units are in the output order of the
	or the RTP payload and reacting to their contents.</t>	decoded pictures corresponding to the access units, as specified in
		<xref target="EVC"/>, and in which NAL units within an access unit
	<ul empty="true"><li>	are in their decoding order.</dd>
	<t>Informative note: The concept of a MANE goes beyond normal routers or gatew	<dt>RTP stream:</dt><dd>See <xref target="RFC7656"/>. Within the
	ays in that a MANE has to be aware of the signaling (e.g., to learn about the pa	scope of this document, one RTP stream is utilized to transport an
	yload type mappings of the media streams), and in that it has to be trusted when	EVC bitstream, which may contain one or more temporal
	working with Secure RTP (SRTP). The advantage of using MANEs is that they allo	sub-layers.</dd>
	w packets to be dropped according to the needs of the media coding. For example	<dt>Transmission order:</dt><dd>The order of packets in ascending
	, if a MANE has to drop packets due to congestion on a certain link, it can iden	RTP sequence number order (in modulo arithmetic). Within an
	tify and remove those packets whose elimination produces the least adverse effec	Aggregation Packet (AP), the NAL unit transmission order is the same a
	t on the user experience. After dropping packets, MANEs must rewrite RTCP packe	s
	ts to match the changes to the RTP stream, as specified in Section 7 of <xref ta	the order of appearance of NAL units in the packet.</dd>
	rget="RFC3550"/>.</t>	</dl>
	</li></ul>	</section>
		</section>
	<t>NAL unit decoding order: A NAL unit order that conforms to the constraints on	<section anchor="abbreviations">
	NAL unit order given in Section 7.4.2.3 in <xref target="EVC"/>, follow the ord	<name>Abbreviations</name>
	er of NAL units in the bitstream.</t>	<dl newline="false" spacing="normal" indent="9">
		<dt>AU</dt>
	<t>NALU-time: The value that the RTP timestamp would have if the NAL unit would	<dd>Access Unit</dd>
	be transported in its own RTP packet.</t>	<dt>AP</dt>
		<dd>Aggregation Packet</dd>
	<t>NAL unit output order: A NAL unit order in which NAL units of different acces	<dt>APS</dt>
	s units are in the output order of the decoded pictures corresponding to the acc	<dd>Adaptation Parameter Set</dd>
	ess units, as specified in <xref target="EVC"/>, and in which NAL units within a	<dt>ATS</dt>
	n access unit are in their decoding order.</t>	<dd>Adaptive Transform Selection</dd>
		<dt>B</dt>
	<t>RTP stream: See <xref target="RFC7656"/>. Within the scope of this document,	<dd>Bi-predictive</dd>
	one RTP stream is utilized to transport a EVC bitstream, which may contain one	<dt>CBR</dt>
	or more temporal sub-layers.</t>	<dd>Constant Bit Rate</dd>
		<dt>CPB</dt>
	<t>Transmission order: The order of packets in ascending RTP sequence number ord	<dd>Coded Picture Buffer</dd>
	er (in modulo arithmetic). Within an aggregation packet, the NAL unit transmiss	<dt>CTB</dt>
	ion order is the same as the order of appearance of NAL units in the packet.</t>	<dd>Coding Tree Block</dd>
		<dt>CTU</dt>
	</section>	<dd>Coding Tree Unit</dd>
	</section>	<dt>CVS</dt>
	<section anchor="abbreviations"><name>Abbreviations</name>	<dd>Coded Video Sequence</dd>
		<dt>DPB</dt>
	<t>AU         Access Unit</t>	<dd>Decoded Picture Buffer</dd>
		<dt>HRD</dt>
	<t>AP         Aggregation Packet</t>	<dd>Hypothetical Reference Decoder</dd>
		<dt>HSS</dt>
	<t>APS        Adaptation Parameter Set</t>	<dd>Hypothetical Stream Scheduler</dd>
		<dt>I</dt>
	<t>ATS        Adaptive Transform Selection</t>	<dd>Intra</dd>
		<dt>IDR</dt>
	<t>B          Bi-predictive</t>	<dd>Instantaneous Decoding Refresh</dd>
		<dt>LSB</dt>
	<t>CBR        Constant Bit Rate</t>	<dd>Least Significant Bit</dd>
		<dt>LTRP</dt>
	<t>CPB        Coded Picture Buffer</t>	<dd>Long-Term Reference Picture</dd>
		<dt>MMVD</dt>
	<t>CTB        Coding Tree Block</t>	<dd>Merge with Motion Vector Difference</dd>
		<dt>MSB</dt>
	<t>CTU        Coding Tree Unit</t>	<dd>Most Significant Bit</dd>
		<dt>NAL</dt>
	<t>CVS        Coded Video Sequence</t>	<dd>Network Abstraction Layer</dd>
		<dt>P</dt>
	<t>DPB        Decoded Picture Buffer</t>	<dd>Predictive</dd>
		<dt>POC</dt>
	<t>HRD        Hypothetical Reference Decoder</t>	<dd>Picture Order Count</dd>
		<dt>PPS</dt>
	<t>HSS        Hypothetical Stream Scheduler</t>	<dd>Picture Parameter Set</dd>
		<dt>QP</dt>
	<t>I          Intra</t>	<dd>Quantization Parameter</dd>
		<dt>RBSP</dt>
	<t>IDR        Instantaneous Decoding Refresh</t>	<dd>Raw Byte Sequence Payload</dd>
		<dt>RGB</dt>
	<t>LSB        Least Significant Bit</t>	<dd>Red, Green, and Blue</dd>
		<dt>SAR</dt>
	<t>LTRP       Long-Term Reference Picture</t>	<dd>Sample Aspect Ratio</dd>
		<dt>SEI</dt>
	<t>MMVD       Merge with Motion Vector Difference</t>	<dd>Supplemental Enhancement Information</dd>
		<dt>SODB</dt>
	<t>MSB        Most Significant Bit</t>	<dd>String Of Data Bits</dd>
		<dt>SPS</dt>
	<t>NAL        Network Abstraction Layer</t>	<dd>Sequence Parameter Set</dd>
		<dt>STRP</dt>
	<t>P          Predictive</t>	<dd>Short-Term Reference Picture</dd>
		<dt>VBR</dt>
	<t>POC        Picture Order Count</t>	<dd>Variable Bit Rate</dd>
		<dt>VCL</dt>
	<t>PPS        Picture Parameter Set</t>	<dd>Video Coding Layer</dd>
		</dl>
	<t>QP         Quantization Parameter</t>	</section>
		</section>
	<t>RBSP       Raw Byte Sequence Payload</t>	<section anchor="RTPPayloadFormat">
		<name>RTP Payload Format</name>
	<t>RGB        Same as GBR</t>	<section anchor="RTPHeaderUsage">
		<name>RTP Header Usage</name>
	<t>SAR        Sample Aspect Ratio</t>	<t>The format of the RTP header is specified in <xref target="RFC3550"/>
		(included as
	<t>SEI        Supplemental Enhancement Information
	</t>

	<t>SODB       String Of Data Bits</t>

	<t>SPS        Sequence Parameter Set</t>

	<t>STRP       Short-Term Reference Picture</t>

	<t>VBR        Variable Bit Rate</t>

	<t>VCL        Video Coding Layer</t>

	</section>
	</section>
	<section anchor="RTPPayloadFormat"><name>RTP Payload Format</name>

	<section anchor="RTPHeaderUsage"><name>RTP Header Usage</name>

	<t>The format of the RTP header is specified in <xref target="RFC3550"/> (reprin
	ted as
	<xref target="rtp-header"/> for convenience). This payload format uses the fiel ds of	<xref target="rtp-header"/> for convenience). This payload format uses the fiel ds of
	the header in a manner consistent with that specification.</t>	the header in a manner consistent with that specification.</t>

		<t>The RTP payload (and the settings for some RTP header bits) for
		APs and Fragmentation Units (FUs) are specified in Sections
		<xref target="aps" format="counter"/> and <xref target="funits" format="counter"
		/>, respectively.</t>


	<t>The RTP payload (and the settings for some RTP header bits) for	<figure anchor="rtp-header">
	aggregation packets and fragmentation units are specified in	<name>RTP Header According to RFC 3550</name>
	<xref target="aps"/> and <xref target="funits"/>, respectively.</t>	<artwork><![CDATA[

	<figure anchor="rtp-header"><sourcecode type="~"><![CDATA[
	0 1 2 3	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\|V=2\|P\|X\| CC \|M\| PT \| sequence number \|	\|V=2\|P\|X\| CC \|M\| PT \| sequence number \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| timestamp \|	\| timestamp \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| synchronization source (SSRC) identifier \|	\| synchronization source (SSRC) identifier \|
	+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+	+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
	\| contributing source (CSRC) identifiers \|	\| contributing source (CSRC) identifiers \|
	\| .... \|	\| .... \|

	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork
		>
	RTP Header According to [RFC3550]	</figure>
	]]></sourcecode></figure>

	<t>The RTP header information to be set according to this RTP payload format is
	set as follows:</t>

	<t>Marker bit (M): 1 bit</t>

	<ul empty="true"><li>
	<t>Set for the last packet of the access unit, carried in the current
	RTP stream. This is in line with the normal use of the M bit in
	video formats to allow an efficient playout buffer handling.</t>
	</li></ul>

	<t>Payload Type (PT): 7 bits</t>

	<ul empty="true"><li>
	<t>The assignment of an RTP payload type for this new payload format
	is outside the scope of this document and will not be specified
	here. The assignment of a payload type has to be performed either
	through the profile used or in a dynamic way.</t>
	</li></ul>

	<t>Sequence Number (SN): 16 bits</t>

	<ul empty="true"><li>
	<t>Set and used in accordance with <xref target="RFC3550"/>.</t>
	</li></ul>

	<t>Timestamp: 32 bits</t>

	<ul empty="true"><li>
	<t>The RTP timestamp is set to the sampling timestamp of the content. A 90 kHz
	clock rate MUST be used. If the NAL unit has no timing properties of its own (
	e.g., parameter sets or certain SEI NAL units), the RTP timestamp MUST be set to
	the RTP timestamp of the coded picture of the access unit in which the NAL unit
	is included. For SEI messages, this information is specified in Annex D of <xr
	ef target="EVC"/>. Receivers MUST use the RTP timestamp for the display process,
	even when the bitstream contains picture timing SEI messages or decoding unit i
	nformation SEI messages as specified in <xref target="EVC"/>.</t>
	</li></ul>

	<t>Synchronization source (SSRC): 32 bits</t>

	<ul empty="true"><li>
	<t>Used to identify the source of the RTP packets. According to this document
	, a single SSRC is used for all parts of a single bitstream.</t>
	</li></ul>

	</section>
	<section anchor="PayloadHeaderUsage"><name>Payload Header Usage</name>

	<t>The first two bytes of the payload of an RTP packet are referred to as the pa
	yload header. The payload header consists of the same fields (F, TID, Reserve a
	nd E) as the NAL unit header as shown in <xref target="NALUnitHeader"/>, irrespe
	ctive of the type of the payload structure.</t>

	<t>The TID value indicates (among other things) the relative importance of an RT
	P packet, for example, because NAL units with larger TID value are not used for
	the decoding of the ones with smaller TID value. A lower value of TID indicates
	a higher importance. More-important NAL units MAY be better protected against tr
	ansmission losses than less-important NAL units.</t>

	</section>
	<section anchor="PayloadStructures"><name>Payload Structures</name>

	<t>Three different types of RTP packet payload structures are specified. A recei
	ver can identify the type of an RTP packet payload through the Type field in the
	payload header.</t>

	<t>The three different payload structures are as follows:</t>

	<t><list style="symbols">
	<t>Single NAL unit packet: Contains a single NAL unit in the payload, and the
	NAL unit header of the NAL unit also serves as the payload header. This payload
	structure is specified in <xref target="SingleNALUnit"/>.</t>
	<t>Aggregation Packet (AP): Contains more than one NAL unit within one access
	unit. This payload structure is specified in <xref target="aps"/>.</t>
	<t>Fragmentation Unit (FU): Contains a subset of a single NAL unit. This paylo
	ad structure is specified in <xref target="funits"/>.</t>
	</list></t>


	<section anchor="SingleNALUnit"><name>Single NAL Unit Packets</name>	<t>The RTP header information to be set according to this RTP payload fo
		rmat is set as follows:</t>
		<dl newline="false" spacing="normal">
		<dt>Marker bit (M):</dt>
		<dd><t>1 bit</t>
		<t>Set for the last packet of the access unit and carried in the
		current RTP stream. This is in line with the normal use of the M
		bit in video formats to allow an efficient playout buffer
		handling.</t>
		</dd>
		<dt>Payload Type (PT):</dt>
		<dd><t>7 bits</t>
		<t>The assignment of an RTP payload type for this new payload format
		is outside the scope of this document and will not be specified
		here. The assignment of a payload type has to be performed either
		through the profile used or in a dynamic way.</t>
		</dd>
		<dt>Sequence Number (SN):</dt>
		<dd><t>16 bits</t>
		<t>Set and used in accordance with <xref target="RFC3550"/>.</t>
		</dd>
		<dt>Timestamp:</dt>
		<dd><t>32 bits</t>
		<t>The RTP timestamp is set to the sampling timestamp of the
		content. A 90 kHz clock rate <bcp14>MUST</bcp14> be used. If the
		NAL unit has no timing properties of its own (e.g., parameter sets
		or certain SEI NAL units), the RTP timestamp <bcp14>MUST</bcp14> be
		set to the RTP timestamp of the coded picture of the access unit in
		which the NAL unit is included. For SEI messages, this information
		is specified in Annex D of <xref target="EVC"/>. Receivers
		<bcp14>MUST</bcp14> use the RTP timestamp for the display process,
		even when the bitstream contains picture timing SEI messages or
		decoding unit information SEI messages as specified in <xref
		target="EVC"/>.</t>
		</dd>
		<dt>Synchronization source (SSRC):</dt>
		<dd><t>32 bits</t>
		<t>Used to identify the source of the RTP packets. According to
		this document, a single SSRC is used for all parts of a single
		bitstream.</t>
		</dd>
		</dl>


	<t>A single NAL unit packet contains exactly one NAL unit, and consists of a pay	</section>
	load header as defined in Table 4 of <xref target="EVC"/> (denoted as PayloadHdr	<section anchor="PayloadHeaderUsage">
	), followed by a conditional 16-bit DONL field (in network byte order), and the	<name>Payload Header Usage</name>
	NAL unit payload data (the NAL unit excluding its NAL unit header) of the contai	<t>The first two bytes of the payload of an RTP packet are referred to
	ned NAL unit, as shown in <xref target="single-nhr"/>.</t>	as the payload header. The payload header consists of the same fields
		(F, TID, Reserve, and E) as the NAL unit header, as shown in <xref
		target="NALUnitHeader"/>, irrespective of the type of the payload
		structure.</t>
		<t>The TID value indicates (among other things) the relative
		importance of an RTP packet, for example, because NAL units with
		larger TID values are not used to decode the ones with
		smaller TID values. A lower value of TID indicates a higher
		importance. More important NAL units <bcp14>MAY</bcp14> be better
		protected against transmission losses than less important NAL
		units.</t>
		</section>
		<section anchor="PayloadStructures">
		<name>Payload Structures</name>
		<t>Three different types of RTP packet payload structures are specified.
		A receiver can identify the type of an RTP packet payload through the Type fiel
		d in the payload header.</t>
		<t>The three different payload structures are as follows:</t>
		<ul>
		<li>Single NAL unit packet: Contains a single NAL unit in
		the payload, and the NAL unit header of the NAL unit also serves as
		the payload header. This payload structure is specified in <xref
		target="SingleNALUnit"/>.</li>
		<li>Aggregation Packet (AP): Contains more than one NAL unit
		within one access unit. This payload structure is specified in
		<xref target="aps"/>.</li>
		<li>Fragmentation Unit (FU): Contains a subset of a single
		NAL unit. This payload structure is specified in <xref
		target="funits"/>.</li>
		</ul>
		<section anchor="SingleNALUnit">
		<name>Single NAL Unit Packets</name>
		<t>A single NAL unit packet contains exactly one NAL unit and
		consists of a payload header as defined in Table 4 of <xref
		target="EVC"/> (denoted as PayloadHdr), followed by a conditional
		16-bit DONL field (in network byte order), and the NAL unit payload
		data (the NAL unit excluding its NAL unit header) of the contained
		NAL unit, as shown in <xref target="single-nhr"/>.</t>


	<figure anchor="single-nhr"><artwork><![CDATA[	<figure anchor="single-nhr">
		<name>The Structure of a Single NAL Unit Packet</name>
		<artwork><![CDATA[
	0 1 2 3	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| PayloadHdr \| DONL (conditional) \|	\| PayloadHdr \| DONL (conditional) \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| \|	\| \|
	\| NAL unit payload data \|	\| NAL unit payload data \|
	\| \|	\| \|
	\| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	\| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| :...OPTIONAL RTP padding \|	\| :...OPTIONAL RTP padding \|

	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
		</figure>
	The Structure of a Single NAL Unit Packet
	]]></artwork></figure>

	<t>The DONL field, when present, specifies the value of the 16 least significant
	bits of the decoding order number of the contained NAL unit. If sprop-max-don-
	diff (defined in <xref target="optionalParameters"/> is greater than 0, the DONL
	field MUST be present, and the variable DON for the contained NAL unit is deriv
	ed as equal to the value of the DONL field. Otherwise (sprop-max-don-diff is eq
	ual to 0), the DONL field MUST NOT be present.</t>

	</section>
	<section anchor="aps"><name>Aggregation Packets (APs)</name>

	<t>Aggregation Packets (APs) enable the reduction of packetization overhead for
	small NAL units, such as most of the non-VCL NAL units, which are often only a f
	ew octets in size.</t>

	<t>An AP aggregates NAL units of one access unit, and it MUST NOT contain NAL un
	its from more than one AU. Each NAL unit to be carried in an AP is encapsulated
	in an aggregation unit. NAL units aggregated in one AP are included in NAL-unit-
	decoding order.</t>


	<t>An AP consists of a payload header, as defined in Table 4 of <xref target="EV	<t>The DONL field, when present, specifies the value of the 16 least s
	C"/> (denoted here as PayloadHdr with Type=56) followed by two or more aggregati	ignificant bits of the decoding order number of the contained NAL unit. If spro
	on units, as shown in <xref target="au-hdr"/>.</t>	p-max-don-diff (defined in <xref target="optionalParameters"/>) is greater than
		0, the DONL field <bcp14>MUST</bcp14> be present, and the variable DON for the c
		ontained NAL unit is derived as equal to the value of the DONL field. Otherwise
		(where sprop-max-don-diff is equal to 0), the DONL field <bcp14>MUST NOT</bcp14
		> be present.</t>
		</section>
		<section anchor="aps">
		<name>Aggregation Packets (APs)</name>
		<t>Aggregation Packets (APs) enable the reduction of packetization ove
		rhead for small NAL units, such as most of the non-VCL NAL units, which are ofte
		n only a few octets in size.</t>
		<t>An AP aggregates NAL units of one access unit, and it <bcp14>MUST N
		OT</bcp14> contain NAL units from more than one AU. Each NAL unit to be carried
		in an AP is encapsulated in an aggregation unit. NAL units aggregated in one AP
		are included in NAL-unit-decoding order.</t>
		<t>An AP consists of a payload header, as defined in Table 4 of <xref
		target="EVC"/> (denoted here as PayloadHdr with Type=56), followed by two or mor
		e aggregation units, as shown in <xref target="au-hdr"/>.</t>


	<figure anchor="au-hdr"><artwork><![CDATA[	<figure anchor="au-hdr">
		<name>The Structure of an Aggregation Packet</name>
		<artwork><![CDATA[
	0 1 2 3	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| PayloadHdr (Type=56) \| \|	\| PayloadHdr (Type=56) \| \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \|	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \|
	\| \|	\| \|
	\| two or more aggregation units \|	\| two or more aggregation units \|
	\| \|	\| \|
	\| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	\| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| :...OPTIONAL RTP padding \|	\| :...OPTIONAL RTP padding \|

	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
		</figure>
	The Structure of an Aggregation Packet

	]]></artwork></figure>

	<t>The fields in the payload header of an AP are set as follows. The F bit MUST
	be equal to 0 if the F bit of each aggregated NAL unit is equal to zero; otherwi
	se, it MUST be equal to 1. The Type field MUST be equal to 56.</t>


	<t>The value of TID MUST be the smallest value of TID of all the aggregated NAL	<t>The fields in the payload header of an AP are set as follows. The F
	units. The value of Reserve and E MUST be equal to 0 for this specification.</t>	bit <bcp14>MUST</bcp14> be equal to 0 if the F bit of each aggregated NAL unit
		is equal to zero; otherwise, it <bcp14>MUST</bcp14> be equal to 1. The Type fiel
		d <bcp14>MUST</bcp14> be equal to 56.</t>
		<t>The value of TID <bcp14>MUST</bcp14> be the smallest value of TID o
		f all the aggregated NAL units. The value of Reserve and E <bcp14>MUST</bcp14> b
		e equal to 0 for this specification.</t>


	<ul empty="true"><li>	<aside><t>Informative note: All VCL NAL units in an AP have the
	<t>Informative note: All VCL NAL units in an AP have the same TID value since	same TID value since they belong to the same access unit. However,
	they belong to the same access unit. However, an AP may contain non-VCL NAL unit	an AP may contain non-VCL NAL units for which the TID value in the
	s for which the TID value in the NAL unit header may be different from the TID v	NAL unit header may be different from the TID value of the VCL NAL
	alue of the VCL NAL units in the same AP.</t>	units in the same AP.</t></aside>
	</li></ul>


	<t>An AP MUST carry at least two aggregation units and can carry as many aggrega	<t>An AP <bcp14>MUST</bcp14> carry at least two aggregation units
	tion units as necessary; however, the total amount of data in an AP obviously MU	and can carry as many aggregation units as necessary; however, the
	ST fit into an IP packet, and the size SHOULD be chosen so that the resulting IP	total amount of data in an AP obviously <bcp14>MUST</bcp14> fit into
	packet is smaller than the path MTU size so to avoid IP layer fragmentation. An	an IP packet, and the size <bcp14>SHOULD</bcp14> be chosen so that
	AP MUST NOT contain FUs specified in <xref target="funits"/>. APs MUST NOT be n	the resulting IP packet is smaller than the path MTU size so to
	ested; i.e., an AP can not contain another AP.</t>	avoid IP layer fragmentation. An AP <bcp14>MUST NOT</bcp14> contain
		FUs specified in <xref target="funits"/>. APs <bcp14>MUST
		NOT</bcp14> be nested; i.e., an AP cannot contain another AP.</t>


	<ul empty="true"><li>	<aside><t>Informative note: If a receiver encounters nested
	<t>Informative note: If a receiver encounters nested Aggregation Packets, whic	APs, which is against the aforementioned
	h is against the aforementioned requirement, it has several options, listed in o	requirement, it has several options, listed in order of ease of
	rder of ease of implementation: 1) Ignore the nested AP; 2) Ignore the nested AP	implementation: 1) ignore the nested AP; 2) ignore the nested AP and
	and report a "packet loss" to the decoder, if such functionality exis	report a "packet loss" to the decoder, if such functionality exists
	ts in the API, 3) Implement support for nested APs and extract the Network Abstr	in the API; and 3) implement support for nested APs and extract the
	action Layer (NAL) units from these nested APs.</t>	NAL units from these nested APs.</t></aside>
	</li></ul>


	<t>The first aggregation unit in an AP consists of a conditional 16-bit DONL fie ld (in network byte order) followed by a 16-bit unsigned size information (in ne twork byte order) that indicates the size of the	<t>The first aggregation unit in an AP consists of a conditional 16-bi t DONL field (in network byte order) followed by a 16-bit unsigned size informat ion (in network byte order) that indicates the size of the
	NAL unit in bytes (excluding these two octets but including the NAL unit header) , followed by the NAL unit itself, including its NAL unit header, as shown in <x ref target="au-first-nhdr"/>.</t>	NAL unit in bytes (excluding these two octets but including the NAL unit header) , followed by the NAL unit itself, including its NAL unit header, as shown in <x ref target="au-first-nhdr"/>.</t>


	<figure anchor="au-first-nhdr"><artwork><![CDATA[	<figure anchor="au-first-nhdr">
		<name>The Structure of the First Aggregation Unit in an AP</name>
		<artwork><![CDATA[
	0 1 2 3	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| : DONL (conditional) \| NALU size \|	\| : DONL (conditional) \| NALU size \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| NALU size \| \|	\| NALU size \| \|
	+-+-+-+-+-+-+-+-+ NAL unit \|	+-+-+-+-+-+-+-+-+ NAL unit \|
	\| \|	\| \|
	\| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	\| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| :	\| :

	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
		</figure>
	The Structure of the First Aggregation Unit in an AP
	]]></artwork></figure>

	<ul empty="true"><li>
	<t>Informative note: The first octet of <xref target="au-first-nhdr"/> (indica
	ted by the first colon) belongs to a previous aggregation unit. It is depicted t
	o emphasize that aggregation units are octet aligned only. Similarly, the NAL un
	it carried in the aggregation unit can terminate at the octet boundary.</t>
	</li></ul>

	<t>The DONL field, when present, specifies the value of the 16 least significant
	bits of the decoding order number of the aggregated NAL unit.</t>


	<t>If sprop-max-don-diff is greater than 0, the DONL field MUST be present in an	<aside><t>Informative note: The first octet of <xref
	aggregation unit that is the first aggregation unit in an AP. The variable DON	target="au-first-nhdr"/> (indicated by the first colon) belongs to a
	for the aggregated NAL unit is derived as equal to the value of the DONL field,	previous aggregation unit. It is depicted to emphasize that
	and the variable DON for an aggregation unit that is not the first aggregation u	aggregation units are octet aligned only. Similarly, the NAL unit
	nit in an AP-aggregated NAL unit is derived as equal to the DON of the preceding	carried in the aggregation unit can terminate at the octet
	aggregated NAL unit in the same AP plus 1 modulo 65536. Otherwise (sprop-max-do	boundary.</t></aside>
	n-diff is equal to 0), the DONL field MUST NOT be present in an aggregation unit
	that is the first aggregation unit in an AP</t>


	<t>An aggregation unit that is not the first aggregation unit in an AP will be f	<t>The DONL field, when present, specifies the value of the 16 least s
	ollowed immediately by a 16-bit unsigned size information (in network byte order	ignificant bits of the decoding order number of the aggregated NAL unit.</t>
	) that indicates the size of the NAL unit in bytes (excluding these two octets b	<t>If sprop-max-don-diff is greater than 0, the DONL field <bcp14>MUST
	ut including the NAL unit header), followed by the NAL unit itself, including it	</bcp14> be present in an aggregation unit that is the first aggregation unit in
	s NAL unit header, as shown in <xref target="au-not-first-nhdr"/>.</t>	an AP. The variable DON for the aggregated NAL unit is derived as equal to the
		value of the DONL field, and the variable Decoding Order Number (DON) for an agg
		regation unit that is not the first aggregation unit in an AP-aggregated NAL uni
		t is derived as equal to the DON of the preceding aggregated NAL unit in the sam
		e AP plus 1 modulo 65536. Otherwise (where sprop-max-don-diff is equal to 0), th
		e DONL field <bcp14>MUST NOT</bcp14> be present in an aggregation unit that is t
		he first aggregation unit in an AP.</t>
		<t>An aggregation unit that is not the first aggregation unit in an AP
		will be followed immediately by a 16-bit unsigned size information (in network
		byte order) that indicates the size of the NAL unit in bytes (excluding these tw
		o octets but including the NAL unit header), followed by the NAL unit itself, in
		cluding its NAL unit header, as shown in <xref target="au-not-first-nhdr"/>.</t>


	<figure anchor="au-not-first-nhdr"><artwork><![CDATA[	<figure anchor="au-not-first-nhdr">
		<name> The Structure of an Aggregation Unit That Is Not the First Agg
		regation Unit in an AP</name>
		<artwork><![CDATA[
	0 1 2 3	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| : NALU size \| NAL unit \|	\| : NALU size \| NAL unit \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \|	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \|
	\| \|	\| \|
	\| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	\| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| :	\| :

	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
		</figure>
	The Structure of an Aggregation Unit That Is Not the First
	Aggregation Unit in an AP
	]]></artwork></figure>


	<ul empty="true"><li>	<aside><t>Informative note: The first octet of <xref
	<t>Informative note: The first octet of <xref target="au-not-first-nhdr"/> (in	target="au-not-first-nhdr"/> (indicated by the first colon) belongs
	dicated by the first colon) belongs to a previous aggregation unit. It is depict	to a previous aggregation unit. It is depicted to emphasize that
	ed to emphasize that aggregation units are octet aligned only. Similarly, the NA	aggregation units are octet aligned only. Similarly, the NAL unit
	L unit carried in the aggregation unit can terminate at the octet boundary.</t>	carried in the aggregation unit can terminate at the octet
	</li></ul>	boundary.</t></aside>


	<t><xref target="au-wout-donl"/> presents an example of an AP that contains two	<t><xref target="au-wout-donl"/> presents an example of an AP that
	aggregation	contains two aggregation units, labeled "NALU 1" and "NALU 2",
	units, labeled as NALU 1 and NALU 2 in the figure, without the DONL field	without the DONL field being present.</t>
	being present.</t>


	<figure anchor="au-wout-donl"><artwork><![CDATA[	<figure anchor="au-wout-donl">
		<name>An Example of an AP Packet Containing Two Aggregation Units wit
		hout the DONL Field</name>
		<artwork><![CDATA[
	0 1 2 3	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| RTP Header \|	\| RTP Header \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| PayloadHdr (Type=56) \| NALU 1 Size \|	\| PayloadHdr (Type=56) \| NALU 1 Size \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| NALU 1 HDR \| \|	\| NALU 1 HDR \| \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NALU 1 Data \|	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NALU 1 Data \|
	\| . . . \|	\| . . . \|
	\| \|	\| \|
	+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| . . . \| NALU 2 Size \| NALU 2 HDR \|	\| . . . \| NALU 2 Size \| NALU 2 HDR \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| NALU 2 HDR \| \|	\| NALU 2 HDR \| \|
	+-+-+-+-+-+-+-+-+ NALU 2 Data \|	+-+-+-+-+-+-+-+-+ NALU 2 Data \|
	\| . . . \|	\| . . . \|
	\| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	\| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| :...OPTIONAL RTP padding \|	\| :...OPTIONAL RTP padding \|

	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
		</figure>
	An Example of an AP Packet Containing
	Two Aggregation Units without the DONL Field
	]]></artwork></figure>


	<t><xref target="au-with-donl"/> presents an example of an AP that contains two	<t><xref target="au-with-donl"/> presents an example of an AP that con
	aggregation	tains two aggregation
	units, labeled as NALU 1 and NALU 2 in the figure, with the DONL field being p	units, labeled "NALU 1" and "NALU 2", with the DONL field being present.</t>
	resent.</t>


	<figure anchor="au-with-donl"><artwork><![CDATA[	<figure anchor="au-with-donl">
		<name>An Example of an AP Containing Two Aggregation Units with the D
		ONL Field</name>
		<artwork><![CDATA[
	0 1 2 3	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| RTP Header \|	\| RTP Header \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| PayloadHdr (Type=56) \| NALU 1 DONL \|	\| PayloadHdr (Type=56) \| NALU 1 DONL \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| NALU 1 Size \| NALU 1 HDR \|	\| NALU 1 Size \| NALU 1 HDR \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| \|	\| \|
	\| NALU 1 Data . . . \|	\| NALU 1 Data . . . \|
	\| \|	\| \|
	+ . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+ . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| : NALU 2 Size \|	\| : NALU 2 Size \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| NALU 2 HDR \| \|	\| NALU 2 HDR \| \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NALU 2 Data \|	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NALU 2 Data \|
	\| \|	\| \|
	\| . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	\| . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| :...OPTIONAL RTP padding \|	\| :...OPTIONAL RTP padding \|

	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
		</figure>
	An Example of an AP Containing
	Two Aggregation Units with the DONL Field
	]]></artwork></figure>

	</section>
	<section anchor="funits"><name>Fragmentation Units</name>

	<t>Fragmentation Units (FUs) are introduced to enable fragmenting a single NAL u
	nit into multiple RTP packets, possibly without cooperation or knowledge of the
	EVC encoder. A fragment of a NAL unit consists of an integer number of consecut
	ive octets of that NAL unit. Fragments of the same NAL unit MUST be sent in con
	secutive order with ascending RTP sequence numbers (with no other RTP packets wi
	thin the same RTP stream being sent between the first and last fragment).</t>

	<t>When a NAL unit is fragmented and conveyed within FUs, it is referred to as a
	fragmented NAL unit. APs MUST NOT be fragmented. FUs MUST NOT be nested; i.e.
	, an FU must not contain a subset of another FU.</t>

	<t>The RTP timestamp of an RTP packet carrying an FU is set to the NALU-time of
	the fragmented NAL unit.</t>


	<t>An FU consists of a payload header as defined in Table 4 of <xref target="EVC	</section>
	"/> (denoted as PayloadHdr with type=57), an FU header of one octet, a condition	<section anchor="funits">
	al 16-bit DONL field (in network byte order), and an FU payload, as shown in <xr	<name>Fragmentation Units (FUs)</name>
	ef target="fu-payload"/>.</t>	<t>FUs are introduced to enable fragmenting a single NAL unit into mul
		tiple RTP packets, possibly without cooperation or knowledge of the EVC encoder.
		A fragment of a NAL unit consists of an integer number of consecutive octets o
		f that NAL unit. Fragments of the same NAL unit <bcp14>MUST</bcp14> be sent in
		consecutive order with ascending RTP sequence numbers (with no other RTP packets
		within the same RTP stream being sent between the first and last fragment).</t>
		<t>When a NAL unit is fragmented and conveyed within FUs, it is referr
		ed to as a fragmented NAL unit. APs <bcp14>MUST NOT</bcp14> be fragmented. FUs
		<bcp14>MUST NOT</bcp14> be nested; i.e., an FU must not contain a subset of ano
		ther FU.</t>
		<t>The RTP timestamp of an RTP packet carrying an FU is set to the NAL
		U-time of the fragmented NAL unit.</t>
		<t>An FU consists of a payload header as defined in Table 4 of <xref t
		arget="EVC"/> (denoted as PayloadHdr with Type=57), an FU header of one octet, a
		conditional 16-bit DONL field (in network byte order), and an FU payload, as sh
		own in <xref target="fu-payload"/>.</t>


	<figure anchor="fu-payload"><artwork><![CDATA[	<figure anchor="fu-payload">
		<name>The Structure of an FU</name>
		<artwork><![CDATA[
	0 1 2 3	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| PayloadHdr (Type=57) \| FU header \| DONL (cond) \|	\| PayloadHdr (Type=57) \| FU header \| DONL (cond) \|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-\|	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-\|
	\| DONL (cond) \| \|	\| DONL (cond) \| \|
	\|-+-+-+-+-+-+-+-+ \|	\|-+-+-+-+-+-+-+-+ \|
	\| FU payload \|	\| FU payload \|
	\| \|	\| \|
	\| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	\| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	\| :...OPTIONAL RTP padding \|	\| :...OPTIONAL RTP padding \|

	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
		</figure>
	The Structure of an FU
	]]></artwork></figure>

	<t>The fields in the payload header are set as follows. The Type field MUST be
	equal to 57. The fields F, TID, Reserve and E MUST be equal to the fields F, TI
	D, Reserve and E, respectively, of the fragmented NAL unit.</t>


	<t>The FU header consists of an S bit, an E bit, and a 6-bit FuType field, as sh	<t>The fields in the payload header are set as follows. The Type fiel
	own in <xref target="fu-header"/>.</t>	d <bcp14>MUST</bcp14> be equal to 57. The fields F, TID, Reserve, and E <bcp14>
		MUST</bcp14> be equal to the fields F, TID, Reserve, and E, respectively, of the
		fragmented NAL unit.</t>
		<t>The FU header consists of an S bit, an E bit, and a 6-bit FuType fi
		eld, as shown in <xref target="fu-header"/>.</t>


	<figure anchor="fu-header"><artwork><![CDATA[	<figure anchor="fu-header">
		<name>The Structure of FU Header</name>
		<artwork><![CDATA[
	0 1 2 3 4 5 6 7	0 1 2 3 4 5 6 7
	+-+-+-+-+-+-+-+-+	+-+-+-+-+-+-+-+-+
	\|S\|E\| FuType \|	\|S\|E\| FuType \|

	+---------------+	+---------------+]]></artwork>
		</figure>
	The Structure of FU Header
	]]></artwork></figure>

	<t>The semantics of the FU header fields are as follows:</t>

	<t>S: 1 bit</t>

	<ul empty="true"><li>
	<t>When set to 1, the S bit indicates the start of a fragmented NAL unit, i.e.
	, the first byte of the FU payload is also the first byte of the payload of the
	fragmented NAL unit. When the FU payload is not the start of the fragmented NAL
	unit payload, the S bit MUST be set to 0.</t>
	</li></ul>

	<t>E: 1 bit</t>

	<ul empty="true"><li>
	<t>When set to 1, the E bit indicates the end of a fragmented NAL unit, i.e.,
	the last byte of the payload is also the last byte of the fragmented NAL unit.
	When the FU payload is not the last fragment of a fragmented NAL unit, the E bit
	MUST be set to 0.</t>
	</li></ul>

	<t>FuType: 6 bits</t>

	<ul empty="true"><li>
	<t>The field FuType MUST be equal to the field Type of the fragmented NAL unit
	.</t>
	</li></ul>

	<t>The DONL field, when present, specifies the value of the 16 least significant
	bits of the decoding order number of the fragmented NAL unit.</t>


	<t>If sprop-max-don-diff is greater than 0, and the S bit is equal to 1, the DON	<t>The semantics of the FU header fields are as follows:</t>
	L field MUST be present in the FU, and the variable DON for the fragmented NAL u	<dl>
	nit is derived as equal to the value of the DONL field. Otherwise (sprop-max-do	<dt>S:</dt>
	n-diff is equal to 0, or the S bit is equal to 0), the DONL field MUST NOT be pr	<dd>
	esent in the FU.</t>	<t>1 bit</t>


	<t>A non-fragmented NAL unit MUST NOT be transmitted in one FU; i.e., the Start	<t>When set to 1, the S bit indicates the start of a fragmented NAL unit, i.e.,
	bit and End bit MUST NOT both be set to 1 in the same FU header.</t>	the first byte of the FU payload is also the first byte of the payload of the fr
		agmented NAL unit. When the FU payload is not the start of the fragmented NAL u
		nit payload, the S bit <bcp14>MUST</bcp14> be set to 0.</t>
		</dd>


	<t>The FU payload consists of fragments of the payload of the fragmented NAL uni	<dt>E:</dt>
	t so that if the FU payloads of consecutive FUs, starting with an FU with the S	<dd>
	bit equal to 1 and ending with an FU with the E bit equal to 1, are sequentially	<t>1 bit</t>
	concatenated, the payload of the fragmented NAL unit can be reconstructed. The
	NAL unit header of the fragmented NAL unit is not included as such in the FU pa
	yload, but rather the information of the NAL unit header of the fragmented NAL u
	nit is conveyed in F, TID, Reserve and E fields of the FU payload headers of the
	FUs and the FuType field of the FU header of the FUs. An FU payload MUST NOT be
	empty.</t>


	<t>If an FU is lost, the receiver SHOULD discard all following fragmentation uni	<t>When set to 1, the E bit indicates the end of a fragmented NAL unit, i.e., th
	ts in transmission order corresponding to the same fragmented NAL unit unless th	e last byte of the payload is also the last byte of the fragmented NAL unit. Wh
	e decoder in the receiver is known to gracefully handle incomplete NAL units.</t	en the FU payload is not the last fragment of a fragmented NAL unit, the E bit <
	>	bcp14>MUST</bcp14> be set to 0.</t>
		</dd>


	<t>A receiver in an endpoint or a MANE MAY aggregate the first n-1 fragments of	<dt>FuType:</dt>
	a NAL unit to an (incomplete) NAL unit, even if fragment n of that NAL unit is n	<dd>
	ot received. In this case, the forbidden_zero_bit of the NAL unit MUST be set to	<t>6 bits</t>
	1 to indicate a syntax violation.</t>


	</section>	<t>The field FuType <bcp14>MUST</bcp14> be equal to the field Type
	</section>	of the fragmented NAL unit.</t>
	<section anchor="DON"><name>Decoding Order Number</name>	</dd>
		</dl>


	<t>For each NAL unit, the variable AbsDon is derived, representing the	<t>The DONL field, when present, specifies the value of the 16 least s
		ignificant bits of the decoding order number of the fragmented NAL unit.</t>
		<t>If sprop-max-don-diff is greater than 0 and the S bit is equal to 1
		, the DONL field <bcp14>MUST</bcp14> be present in the FU, and the variable DON
		for the fragmented NAL unit is derived as equal to the value of the DONL field.
		Otherwise (where sprop-max-don-diff is equal to 0, or where the S bit is equal
		to 0), the DONL field <bcp14>MUST NOT</bcp14> be present in the FU.</t>
		<t>A non-fragmented NAL unit <bcp14>MUST NOT</bcp14> be transmitted in
		one FU; i.e., the S-bit and E-bit <bcp14>MUST NOT</bcp14> both be set to 1 in t
		he same FU header.</t>
		<t>The FU payload consists of fragments of the payload of the fragment
		ed NAL unit so that if the FU payloads of consecutive FUs, starting with an FU w
		ith the S bit equal to 1 and ending with an FU with the E bit equal to 1, are se
		quentially concatenated, the payload of the fragmented NAL unit can be reconstru
		cted. The NAL unit header of the fragmented NAL unit is not included as such in
		the FU payload. Instead, the information of the NAL unit header of the fragment
		ed NAL unit is conveyed in F, TID, Reserve, and E fields of the FU payload heade
		rs of the FUs and the FuType field of the FU header of the FUs. An FU payload <b
		cp14>MUST NOT</bcp14> be empty.</t>
		<t>If an FU is lost, the receiver <bcp14>SHOULD</bcp14> discard all fo
		llowing fragmentation units in transmission order corresponding to the same frag
		mented NAL unit unless the decoder in the receiver is known to gracefully handle
		incomplete NAL units.</t>
		<t>A receiver in an endpoint or a MANE <bcp14>MAY</bcp14> aggregate th
		e first n-1 fragments of a NAL unit to an (incomplete) NAL unit, even if fragmen
		t n of that NAL unit is not received. In this case, the forbidden_zero_bit of th
		e NAL unit <bcp14>MUST</bcp14> be set to 1 to indicate a syntax violation.</t>
		</section>
		</section>
		<section anchor="DON">
		<name>Decoding Order Number</name>
		<t>For each NAL unit, the variable AbsDon is derived; it represents the
	decoding order number that is indicative of the NAL unit decoding	decoding order number that is indicative of the NAL unit decoding
	order.</t>	order.</t>

		<t>Let NAL unit n be the n-th NAL unit in transmission order within an
	<t>Let NAL unit n be the n-th NAL unit in transmission order within an
	RTP stream.</t>	RTP stream.</t>

		<t>If sprop-max-don-diff is equal to 0, then AbsDon[n] (the value of Abs
	<t>If sprop-max-don-diff is equal to 0, AbsDon[n], the value of AbsDon for NAL u	Don for NAL unit n) is derived as equal to n.</t>
	nit n, is derived as equal to n.</t>	<t>Otherwise (where sprop-max-don-diff is greater than 0), AbsDon[n] is
		derived as follows, where DON[n] is the value
	<t>Otherwise (sprop-max-don-diff is greater than 0), AbsDon[n] is derived as fol
	lows, where DON[n] is the value
	of the variable DON for NAL unit n:</t>	of the variable DON for NAL unit n:</t>

		<ul spacing="normal">
		<li>If n is equal to 0 (i.e., NAL unit n is the very first NAL unit
		in transmission order), AbsDon[0] is set equal to DON[0].</li>
		<li><t>Otherwise (where n is greater than 0), the following applies
		for derivation of AbsDon[n]:</t>


	<t><list style="symbols">	<artwork><![CDATA[
	<t>If n is equal to 0 (i.e., NAL unit n is the very first NAL unit	If DON[n] == DON[n-1],
	in transmission order), AbsDon[0] is set equal to DON[0].</t>	AbsDon[n] = AbsDon[n-1]
	<t>Otherwise (n is greater than 0), the following applies for
	derivation of AbsDon[n]:</t>
	</list></t>

	<figure><artwork><![CDATA[
	If DON[n] == DON[n-1],
	AbsDon[n] = AbsDon[n-1]

	If (DON[n] > DON[n-1] and DON[n] - DON[n-1] < 32768),
	AbsDon[n] = AbsDon[n-1] + DON[n] - DON[n-1]

	If (DON[n] < DON[n-1] and DON[n-1] - DON[n] >= 32768),
	AbsDon[n] = AbsDon[n-1] + 65536 - DON[n-1] + DON[n]

	If (DON[n] > DON[n-1] and DON[n] - DON[n-1] >= 32768),
	AbsDon[n] = AbsDon[n-1] - (DON[n-1] + 65536 - DON[n])

	If (DON[n] < DON[n-1] and DON[n-1] - DON[n] < 32768),
	AbsDon[n] = AbsDon[n-1] - (DON[n-1] - DON[n])
	]]></artwork></figure>

	<t>For any two NAL units m and n, the following applies:</t>

	<t><list style="symbols">
	<t>AbsDon[n] greater than AbsDon[m] indicates that NAL unit n follows NAL unit
	m in NAL unit decoding order.</t>
	<t>When AbsDon[n] is equal to AbsDon[m], the NAL unit decoding order of the tw
	o NAL units can be in either order.</t>
	<t>AbsDon[n] less than AbsDon[m] indicates that NAL unit n precedes NAL unit m
	in decoding order. <vspace blankLines='1'/>
	<ul empty="true"><li>
	<ul empty="true"><li>
	<t>Informative note: When two consecutive NAL units in the NAL
	unit decoding order has different values of AbsDon, the
	the absolute difference between the two AbsDon values may be
	greater than or equal to 1.</t>
	</li></ul>
	</li></ul>
	<vspace blankLines='1'/>
	<ul empty="true"><li>
	<ul empty="true"><li>
	<t>Informative note: There are multiple reasons to allow for the absolut
	e difference of the values of AbsDon for two consecutive NAL units in the NAL un
	it decoding order to be greater than one. An increment by one is not required, a
	s at the time of associating values of AbsDon to NAL units, it may not be known
	whether all NAL units are to be delivered to the receiver. For example, a gatewa
	y might not forward VCL NAL units of higher sub-layers or some SEI NAL units whe
	n there is congestion in the network. In another example, the first intra-coded
	picture of a pre-encoded clip is transmitted in advance to ensure that it is rea
	dily available in the receiver. When transmitting the first intra-coded picture,
	the originator still determines how many NAL units will be encoded before the f
	irst intra-coded picture of the pre-encoded clip follows in decoding order. Thus
	, the values of AbsDon for the NAL units of the first intra-coded picture of the
	pre-encoded clip have to be estimated when they are transmitted, and gaps in th
	e values of AbsDon may occur.</t>
	</li></ul>
	</li></ul>
	</t>
	</list></t>

	</section>
	</section>
	<section anchor="PacketizationRules"><name>Packetization Rules</name>

	<t>The following packetization rules apply:</t>

	<t><list style="symbols">
	<t>If sprop-max-don-diff is greater than 0, the transmission order of NAL unit
	s carried in the RTP stream MAY be different from the NAL unit decoding order. O
	therwise (sprop-max-don-diff equals 0), the transmission order of NAL units carr
	ied in the RTP stream MUST be the same as the NAL unit decoding order.</t>
	<t>A NAL unit of small size SHOULD be encapsulated in an aggregation packet to
	gether with one or more other NAL units to avoid the unnecessary packetization o
	verhead for small NAL units. For example, non-VCL NAL units, such as access unit
	delimiters, parameter sets, or SEI NAL units, are typically small and can often
	be aggregated with VCL NAL units without violating MTU size constraints.</t>
	<t>Each non-VCL NAL unit SHOULD, when possible from an MTU size match viewpoin
	t, be encapsulated in an aggregation packet with its associated VCL NAL unit, as
	typically, a non-VCL NAL unit would be meaningless without the associated VCL N
	AL unit being available.</t>
	<t>For carrying precisely one NAL unit in an RTP packet, a single NAL unit pac
	ket MUST be used.</t>
	</list></t>

	</section>
	<section anchor="DepacketizationProcess"><name>De-packetization Process</name>

	<t>The general concept behind de-packetization is to get the NAL units out of th
	e RTP packets in an RTP stream and pass them to the decoder in the NAL unit deco
	ding order.</t>

	<t>The de-packetization process is implementation dependent. Therefore, the foll
	owing description should be seen as an example of a suitable implementation. Oth
	er schemes may also be used as long as the output for the same input is the same
	as the process described below. The output is the same when the set of output N
	AL units and their order are both identical. Optimizations relative to the descr
	ibed algorithms are possible.</t>

	<t>All normal RTP mechanisms related to buffer management apply. In particular,
	duplicated or outdated RTP packets (as indicated by the RTP sequence number and
	the RTP timestamp) are removed. To determine the exact time for decoding, factor
	s such as a possible intentional delay to allow for proper inter-stream synchron
	ization, MUST be factored in.</t>

	<t>NAL units with NAL unit type values in the range of 0 to 55, inclusive, may b
	e passed to the decoder. NAL-unit-like structures with NAL unit type values in t
	he range of 56 to 62, inclusive, MUST NOT be passed to the decoder.</t>

	<t>The receiver includes a receiver buffer, which is used to compensate for tran
	smission delay jitter within individual RTP streams and to reorder NAL units fro
	m transmission order to the NAL unit decoding order. In this section, the receiv
	er operation is described under the assumption that there is no transmission del
	ay jitter within an RTP stream. To clarify the distinction from a practical rece
	iver buffer, which is also used to compensate for transmission delay jitter, the
	buffer in this section will henceforth be referred to as the de-packetization b
	uffer. Receivers should also prepare for transmission delay jitter; that is, eit
	her reserve separate buffers for transmission delay jitter buffering and de-pack
	etization buffering or use a receiver buffer for both transmission delay jitter
	and de-packetization. Moreover, receivers should take transmission delay jitter
	into account in the buffering operation, e.g., by additional initial buffering b
	efore starting of decoding and playback.</t>

	<t>The de-packetization process extracts the NAL units from the RTP packets in a
	n RTP stream as follows. When an RTP packet carries a single NAL unit packet, th
	e payload of the RTP packet is extracted as a single NAL unit, excluding the DON
	L field, i.e., third and fourth bytes, when sprop-max-don-diff is greater than 0
	. When an RTP packet carries an aggregation packet, several NAL units are extrac
	ted from the payload of the RTP packet. In this case, each NAL unit corresponds
	to the part of the payload of each aggregation unit that follows the NALU size f
	ield, as described in <xref target="aps"/>. When an RTP packet carries a Fragmen
	tation Unit (FU), all RTP packets from the first FU (with the S field equal to 1
	) of the fragmented NAL unit up to the last FU (with the E field equal to 1) of
	the fragmented NAL unit are collected. The NAL unit is extracted from these RTP
	packets by concatenating all FU payloads in the same order as the corresponding
	RTP packets and appending the NAL unit header with the fields F and TID set to e
	qual the values of the fields F and TID in the payload header of the FUs, respec
	tively, and with the NAL unit type set equal to the value of the field FuType in
	the FU header of the FUs, as described in <xref target="funits"/>.</t>

	<t>When sprop-max-don-diff is equal to 0, the de-packetization buffer size is ze
	ro bytes, and the NAL units carried in the single RTP stream are directly passed
	to the decoder in their transmission order, which is identical to their decodin
	g order.</t>

	<t>When sprop-max-don-diff is greater than 0, the process described in the remai
	nder of this section applies.</t>

	<t>The receiver has two buffering states: initial buffering and buffering while
	playing. Initial buffering starts when the reception is initialized. After initi
	al buffering, decoding and playback are started, and the buffering-while-playing
	mode is used.</t>

	<t>Regardless of the buffering state, the receiver stores incoming NAL units in
	reception order into the de-packetization buffer. NAL units carried in RTP packe
	ts are stored in the de-packetization buffer individually, and the value of AbsD
	on is calculated and stored for each NAL unit.</t>

	<t>Initial buffering lasts until the difference between the greatest and smalles
	t AbsDon values of the NAL units in the de-packetization buffer is greater than
	or equal to the value of sprop-max-don-diff.</t>

	<t>After initial buffering, whenever the difference between the greatest and sma
	llest AbsDon values of the NAL units in the de-packetization buffer is greater t
	han or equal to the value of sprop-max-don-diff, the following operation is repe
	atedly applied until this difference is smaller than sprop-max-don-diff:</t>

	<t><list style="symbols">
	<t>The NAL unit in the de-packetization buffer with the smallest value of AbsD
	on is removed from the de-packetization buffer and passed to the decoder.</t>
	</list></t>

	<t>When no more NAL units are flowing into the de-packetization buffer, all NAL
	units remaining in the de-packetization buffer are removed from the buffer and p
	assed to the decoder in the order of increasing AbsDon values.</t>

	<!-- Section 7 -->

	</section>
	<section anchor="PayloadFormatParameters"><name>Payload Format Parameters</name>

	<t>This section specifies the optional parameters. A mapping of the parameters w
	ith Session Description Protocol (SDP) <xref target="RFC8866"/> is also provided
	for applications that use SDP.</t>

	<t>Parameters starting with the string "sprop" for stream properties c
	an be used by a sender to provide a receiver with the properties of the stream t
	hat is or will be sent. The media sender (and not the receiver) selects whether,
	and with what values, "sprop" parameters are being sent. This uncommo
	n characteristic of the "sprop" parameters may not be intuitive in the
	context of some signaling protocol concepts, especially with offer/answer. Ple
	ase see <xref target="sdpoa"/> for guidance specific to the use of sprop paramet
	ers in the Offer/Answer case.</t>

	<!-- Section 7.1 -->

	<section anchor="oparams"><name>Media Type Registration</name>

	<t>The receiver MUST ignore any parameter unspecified in this document.</t>

	<t>Type name:           &
	#160;video</t>

	<t>Subtype name:         evc</t>

	<t>Required parameters: N/A</t>

	<t>Optional parameters: profile-id, level-id, toolset-id, max-recv-level-id, spr
	op-sps, sprop-pps, sprop-sei, sprop-max-don-diff, sprop-depack-buf-bytes, depack
	-buf-cap (refer to <xref target="optionalParameters"/> for definitions)</t>

	<t>Encoding considerations:</t>

	<ul empty="true"><li>
	<t>This type is only defined for transfer via RTP (RFC 3550).</t>
	</li></ul>

	<t>Security considerations:</t>

	<ul empty="true"><li>
	<t>See <xref target="Security"/> of RFC XXXX.</t>
	</li></ul>

	<t>Interoperability considerations: N/A</t>

	<t>Published specification:</t>

	<ul empty="true"><li>
	<t>Please refer to RFC XXXX and EVC standard <xref target="EVC"/>.</t>
	</li></ul>

	<t>Applications that use this media type:</t>

	<ul empty="true"><li>
	<t>Any application that relies on EVC-based video services over RTP</t>
	</li></ul>

	<t>Fragment identifier considerations: N/A</t>

	<t>Additional information: N/A</t>

	<t>Person & email address to contact for further information:</t>

	<ul empty="true"><li>
	<t>Stephan Wenger (stewe@stewe.org)</t>
	</li></ul>

	<t>Intended usage: COMMON</t>

	<t>Restrictions on usage: N/A</t>

	<t>Author: See Authors' Addresses section of RFC XXXX.</t>

	<t>Change controller:</t>

	<ul empty="true"><li>
	<t>IETF <avtcore@ietf.org></t>
	</li></ul>

	<!-- Section 7.2 -->

	</section>
	<section anchor="optionalParameters"><name>Optional Parameters Definition</name>

	<t>profile-id, level-id, toolset-id:</t>

	<ul empty="true"><li>
	<t>These parameters indicate the profile, the level, and constraints of the bi
	tstream carried by the RTP stream, or a specific set of the profile, the level,
	and constraints the receiver supports.</t>
	</li></ul>

	<ul empty="true"><li>
	<t>More specifications of these parameters, including how they relate to synta
	x elements specified in <xref target="EVC"/> are provided below.</t>
	</li></ul>

	<t>profile-id:</t>

	<ul empty="true"><li>
	<t>When profile-id is not present, a value of 0 (i.e., the Baseline profile) M
	UST be inferred.</t>
	</li></ul>

	<ul empty="true"><li>
	<t>When used to indicate properties of a bitstream, profile-id MUST be derived
	from the profile_idc in the SPS.</t>
	</li></ul>

	<ul empty="true"><li>
	<t>EVC bitstreams transported over RTP using the technologies of this document
	SHOULD refer only to SPSs that have the same value in profile_idc, unless the s
	ender has a priori knowledge that a receiver can correctly decode the EVC bitstr
	eam with different profile_idc values (for example in walled garden scenarios).
	As exceptions to this rule, if the receiver is known to support Baseline profil
	e, a bitstream could safely end with CVS referring to an SPS wherein profile_idc
	indicates the Baseline Still Picture profile. A similar exception can be made
	for Main profile and Main Still picture profile.</t>
	</li></ul>

	<t>level-id:</t>

	<ul empty="true"><li>
	<t>When level-id is not present, a value of 90 (corresponding to level 3, whic
	h allows for approximately SD TV resolution and frame rates; for details please
	see Annex A of EVC) MUST be inferred.</t>
	</li></ul>

	<ul empty="true"><li>
	<t>When used to indicate properties of a bitstream, level-id MUST be derived f
	rom the level_idc in the SPS.</t>
	</li></ul>

	<ul empty="true"><li>
	<t>If the level-id parameter is used for capability exchange, the following ap
	plies. If max-recv-level-id is not present, the default level defined by level-i
	d indicates the highest level the codec wishes to support. Otherwise, max-recv-l
	evel-id indicates the highest level the codec supports for receiving. For either
	receiving or sending, all levels that are lower than the highest level supporte
	d MUST also be supported.</t>
	</li></ul>

	<t>toolset-id:</t>

	<ul empty="true"><li>
	<t>This parameter is a base64 encoding (Section 4 of <xref target="RFC4648"></
	xref>) representation of a 64 bit unsigned integer bit mask derived from the con
	catenation, in network byte order, of the syntax elements toolset_idc_h and tool
	set_idc_l. When used to indicate properties of a bitstream, its value MUST be d
	erived from toolset_idh_h and toolset_idc_l in the sequence parameter set.</t>
	</li></ul>

	<t>max-recv-level-id:</t>

	<ul empty="true"><li>
	<t>This parameter MAY be used to indicate the highest level a receiver support
	s.</t>
	</li></ul>

	<t>The value of max-recv-level-id MUST be in the range of 0 to 255, inclusive.P.
	</t>

	<t>When max-recv-level-id is not present, the value is inferred to be equal to l
	evel-id.</t>

	<t>max-recv-level-id MUST NOT be present when the highest level the receiver sup
	ports is not higher than the default level.</t>

	<t>sprop-sps:</t>

	<ul empty="true"><li>
	<t>This parameter MAY be used to convey sequence parameter set NAL units of th
	e bitstream for out-of-band transmission of sequence parameter sets. The value
	of the parameter is a comma-separated (',') list of base64 encoding (Sec
	tion 4 of <xref target="RFC4648"/>) representations of the sequence parameter se
	t NAL units as specified in Section 7.3.2.1 of <xref target="EVC"/>.</t>
	</li></ul>

	<t>sprop-pps:</t>

	<ul empty="true"><li>
	<t>This parameter MAY be used to convey picture parameter set NAL units of the
	bitstream for out-of-band transmission of picture parameter sets. The value of
	the parameter is a comma-separated (',') list of base64 encoding (Secti
	on 4 of <xref target="RFC4648"/>) representations of the picture parameter set N
	AL units as specified in Section 7.3.2.2 of <xref target="EVC"/>.</t>
	</li></ul>

	<t>sprop-sei:</t>

	<ul empty="true"><li>
	<t>This parameter MAY be used to convey one or more SEI messages that describe
	bitstream characteristics. When present, a decoder can rely on the bitstream c
	haracteristics that are described in the SEI messages for the entire duration of
	the session, independently from the persistence scopes of the SEI messages as s
	pecified in <xref target="VSEI"/>.</t>
	</li></ul>

	<ul empty="true"><li>
	<t>The value of the parameter is a comma-separated (',') list of base6
	4 encoding (Section 4 of <xref target="RFC4648"/>) representations of SEI NAL un
	its as specified in <xref target="VSEI"/>.</t>
	</li></ul>

	<ul empty="true"><li>
	<ul empty="true"><li>
	<t>Informative note: Intentionally, no list of applicable or inapplicable SE
	I messages is specified here. Conveying certain SEI messages in sprop-sei may b
	e sensible in some application scenarios and meaningless in others. However, a
	few examples are described below:</t>
	</li></ul>
	</li></ul>

	<ul empty="true"><li>
	<ul empty="true"><li>
	<t>1) In an environment where the bitstream was created from film-based sour
	ce material, and no splicing is going to occur during the lifetime of the sessio
	n, the film grain characteristics SEI message is likely meaningful, and sending
	it in sprop-sei rather than in the bitstream at each entry point may help with s
	aving bits and allows one to configure the renderer only once, avoiding unwanted
	artifacts.</t>
	</li></ul>
	</li></ul>

	<ul empty="true"><li>
	<ul empty="true"><li>
	<t>2) Examples for SEI messages that would be meaningless to be conveyed in
	sprop-sei include the decoded picture hash SEI message (it is close to impossibl
	e that all decoded pictures have the same hashtag) or the filler payload SEI mes
	sage (as there is no point in just having more bits in SDP).</t>
	</li></ul>
	</li></ul>

	<t>sprop-max-don-diff:</t>

	<ul empty="true"><li>
	<t>If there is no NAL unit naluA that is followed in transmission order by any
	NAL unit preceding naluA in decoding order (i.e., the transmission order of the
	NAL units is the same as the decoding order), the value of this parameter MUST
	be equal to 0.</t>
	</li></ul>

	<ul empty="true"><li>
	<t>Otherwise, this parameter specifies the maximum absolute difference between
	the decoding order number (i.e., AbsDon) values of any two NAL units naluA and
	naluB, where naluA follows naluB in decoding order and precedes naluB in transmi
	ssion order.</t>
	</li></ul>

	<ul empty="true"><li>
	<t>The value of sprop-max-don-diff MUST be an integer in the range of 0 to 327
	67, inclusive.</t>
	</li></ul>

	<ul empty="true"><li>
	<t>When not present, the value of sprop-max-don-diff is inferred to be equal t
	o 0.</t>
	</li></ul>

	<t>sprop-depack-buf-bytes:</t>

	<ul empty="true"><li>
	<t>This parameter signals the required size of the de-packetization buffer in
	units of bytes. The value of the parameter MUST be greater than or equal to the
	maximum buffer occupancy (in units of bytes) of the de-packetization buffer as
	specified in Section 6.</t>
	</li></ul>

	<ul empty="true"><li>
	<t>The value of sprop-depack-buf-bytes MUST be an integer in the range of 0 to
	4294967295, inclusive.</t>
	</li></ul>

	<ul empty="true"><li>
	<t>When sprop-max-don-diff is present and greater than 0, this parameter MUST
	be present and the value MUST be greater than 0. When not present, the value of
	sprop-depack-buf-bytes is inferred to be equal to 0.</t>
	</li></ul>


	<ul empty="true"><li>	If (DON[n] > DON[n-1] and DON[n] - DON[n-1] < 32768),
	<ul empty="true"><li>	AbsDon[n] = AbsDon[n-1] + DON[n] - DON[n-1]
	<t>Informative note: The value of sprop-depack-buf-bytes indicates the requi
	red size of the de-packetization buffer only. When network jitter can occur, an
	appropriately sized jitter buffer has to be available as well.</t>
	</li></ul>
	</li></ul>


	<t>depack-buf-cap:</t>	If (DON[n] < DON[n-1] and DON[n-1] - DON[n] >= 32768),
		AbsDon[n] = AbsDon[n-1] + 65536 - DON[n-1] + DON[n]


	<ul empty="true"><li>	If (DON[n] > DON[n-1] and DON[n] - DON[n-1] >= 32768),
	<t>This parameter signals the capabilities of a receiver implementation and in	AbsDon[n] = AbsDon[n-1] - (DON[n-1] + 65536 - DON[n])
	dicates the amount of de-packetization buffer space in units of bytes that the r
	eceiver has available for reconstructing the NAL unit decoding order from NAL un
	its carried in the RTP stream. A receiver is able to handle any RTP stream for
	which the value of the sprop-depack-buf-bytes parameter is smaller than or equal
	to this parameter.</t>
	</li></ul>


	<ul empty="true"><li>	If (DON[n] < DON[n-1] and DON[n-1] - DON[n] < 32768),
	<t>When not present, the value of depack-buf-cap is inferred to be equal to 42	AbsDon[n] = AbsDon[n-1] - (DON[n-1] - DON[n])
	94967295. The value of depack-buf-cap MUST be an integer in the range of 1 to 4	]]></artwork></li>
	294967295, inclusive.</t>	</ul>
	</li></ul>	<t>For any two NAL units (m and n), the following applies:</t>
		<ul spacing="normal">
		<li>When AbsDon[n] is greater than AbsDon[m], the NAL unit n
		follows NAL unit m in NAL unit decoding order.</li>
		<li>When AbsDon[n] is equal to AbsDon[m], the NAL unit decoding
		order of the two NAL units can be in either order.</li>
		<li>When AbsDon[n] is less than AbsDon[m], the NAL unit n precedes
		NAL unit m in decoding order.</li>
		</ul>


	<ul empty="true"><li>	<aside><t>Informative note: When two consecutive NAL units in
	<ul empty="true"><li>	the NAL unit decoding order has different values of AbsDon, the
	<t>Informative note: depack-buf-cap indicates the maximum possible size of t	absolute difference between the two AbsDon values may be greater than
	he de-packetization buffer of the receiver only, without allowing for network ji	or equal to 1.</t></aside>
	tter.</t>
	</li></ul>
	</li></ul>


	<!-- Section 7.3 -->	<aside><t>Informative note: There are multiple reasons to allow
		the absolute difference of the values of AbsDon for two
		consecutive NAL units in the NAL unit decoding order to be greater
		than one. An increment by one is not required as at the time of
		associating values of AbsDon to NAL units, it may not be known whether
		all NAL units are to be delivered to the receiver. For example, a
		gateway might not forward VCL NAL units of higher sub-layers or some
		SEI NAL units when there is congestion in the network. In another
		example, the first intra-coded picture of a pre-encoded clip is
		transmitted in advance to ensure that it is readily available in the
		receiver. When transmitting the first intra-coded picture, the
		originator still determines how many NAL units will be encoded before
		the first intra-coded picture of the pre-encoded clip follows in
		decoding order. Thus, the values of AbsDon for the NAL units of the
		first intra-coded picture of the pre-encoded clip have to be estimated
		when they are transmitted and gaps in the values of AbsDon may
		occur.</t></aside>


		</section>
		</section>
		<section anchor="PacketizationRules">
		<name>Packetization Rules</name>
		<t>The following packetization rules apply:</t>
		<ul spacing="normal">
		<li>If sprop-max-don-diff is greater than 0, the transmission order of
		NAL units carried in the RTP stream <bcp14>MAY</bcp14> be different
		from the NAL unit decoding order. Otherwise (where sprop-max-don-diff
		equals 0), the transmission order of NAL units carried in the RTP
		stream <bcp14>MUST</bcp14> be the same as the NAL unit decoding
		order.</li>
		<li>A NAL unit of small size <bcp14>SHOULD</bcp14> be encapsulated in
		an AP together with one or more other NAL units to avoid the
		unnecessary packetization overhead for small NAL units. For example,
		non-VCL NAL units, such as access unit delimiters, parameter sets, or
		SEI NAL units, are typically small and can often be aggregated with
		VCL NAL units without violating MTU size constraints.</li>
		<li>Each non-VCL NAL unit <bcp14>SHOULD</bcp14>, when possible from an
		MTU size match viewpoint, be encapsulated in an AP with its associated
		VCL NAL unit as, typically, a non-VCL NAL unit would be meaningless
		without the associated VCL NAL unit being available.</li>
		<li>A single NAL unit packet <bcp14>MUST</bcp14> be used for carrying
		precisely one NAL unit in an RTP packet.</li>
		</ul>
		</section>
		<section anchor="DepacketizationProcess">
		<name>De-packetization Process</name>
		<t>The general concept behind de-packetization is to get the NAL units out
		of the RTP packets in an RTP stream and pass them to the decoder in the NAL uni
		t decoding order.</t>
		<t>The de-packetization process is implementation dependent. Therefore, th
		e following description should be seen as an example of a suitable implementatio
		n. Other schemes may also be used as long as the output for the same input is th
		e same as the process described below. The output is the same when the set of ou
		tput NAL units and their order are both identical. Optimizations relative to the
		described algorithms are possible.</t>
		<t>All normal RTP mechanisms related to buffer management apply. In partic
		ular, duplicated or outdated RTP packets (as indicated by the RTP sequence numbe
		r and the RTP timestamp) are removed. To determine the exact time for decoding,
		factors such as a possible intentional delay to allow for proper inter-stream sy
		nchronization must be considered.</t>
		<t>NAL units with NAL unit type values in the range of 0 to 55, inclusive,
		may be passed to the decoder. NAL-unit-like structures with NAL unit type value
		s in the range of 56 to 62, inclusive, <bcp14>MUST NOT</bcp14> be passed to the
		decoder.</t>
		<t>The receiver includes a receiver buffer, which is used to compensate fo
		r transmission delay jitter within individual RTP streams and to reorder NAL uni
		ts from transmission order to the NAL unit decoding order. In this section, the
		receiver operation is described under the assumption that there is no transmissi
		on delay jitter within an RTP stream. To clarify the distinction from a practica
		l receiver buffer, which is also used to compensate for transmission delay jitte
		r, the buffer in this section will henceforth be referred to as the "de-packetiz
		ation" buffer. Receivers should also prepare for transmission delay jitter; that
		is, either reserve separate buffers for transmission delay jitter buffering and
		de-packetization buffering, or use a receiver buffer for both transmission dela
		y jitter and de-packetization. Moreover, receivers should take transmission dela
		y jitter into account in the buffering operation, e.g., by additional initial bu
		ffering before starting decoding and playback.</t>
		<t>The de-packetization process extracts the NAL units from the RTP packet
		s in an RTP stream as follows. When an RTP packet carries a single NAL unit pack
		et, the payload of the RTP packet is extracted as a single NAL unit, excluding t
		he DONL field, i.e., third and fourth bytes, when sprop-max-don-diff is greater
		than 0. When an RTP packet carries an AP, several NAL units are extracted from t
		he payload of the RTP packet. In this case, each NAL unit corresponds to the par
		t of the payload of each aggregation unit that follows the NALU size field, as d
		escribed in <xref target="aps"/>. When an RTP packet carries a Fragmentation Uni
		t (FU), all RTP packets from the first FU (with the S field equal to 1) of the f
		ragmented NAL unit up to the last FU (with the E field equal to 1) of the fragme
		nted NAL unit are collected. The NAL unit is extracted from these RTP packets by
		concatenating all FU payloads in the same order as the corresponding RTP packet
		s and appending the NAL unit header with the fields F and TID set to equal the v
		alues of the fields F and TID in the payload header of the FUs, respectively, an
		d with the NAL unit type set equal to the value of the field FuType in the FU he
		ader of the FUs, as described in <xref target="funits"/>.</t>
		<t>When sprop-max-don-diff is equal to 0, the de-packetization buffer size
		is zero bytes, and the NAL units carried in the single RTP stream are directly
		passed to the decoder in their transmission order, which is identical to their d
		ecoding order.</t>
		<t>When sprop-max-don-diff is greater than 0, the process described in the
		remainder of this section applies.</t>
		<t>The receiver has two buffering states: initial buffering and buffering
		while playing. Initial buffering starts when the reception is initialized. After
		initial buffering, decoding and playback are started, and the buffering-while-p
		laying mode is used.</t>
		<t>Regardless of the buffering state, the receiver stores incoming NAL uni
		ts in reception order into the de-packetization buffer. NAL units carried in RTP
		packets are stored in the de-packetization buffer individually, and the value o
		f AbsDon is calculated and stored for each NAL unit.</t>
		<t>Initial buffering lasts until the difference between the greatest and s
		mallest AbsDon values of the NAL units in the de-packetization buffer is greater
		than or equal to the value of sprop-max-don-diff.</t>
		<t>After initial buffering, whenever the difference between the greatest a
		nd smallest AbsDon values of the NAL units in the de-packetization buffer is gre
		ater than or equal to the value of sprop-max-don-diff, the following operation i
		s repeatedly applied until this difference is smaller than sprop-max-don-diff:</
		t>
		<t indent="3">The NAL unit in the de-packetization buffer with the smallest valu
		e of AbsDon is removed from the de-packetization buffer and passed to the decode
		r.</t>
		<t>When no more NAL units are flowing into the de-packetization buffer, al
		l NAL units remaining in the de-packetization buffer are removed from the buffer
		and passed to the decoder in the order of increasing AbsDon values.</t>
	</section>	</section>

	<section anchor="sdp-parameters"><name>SDP Parameters</name>	<section anchor="PayloadFormatParameters">
		<name>Payload Format Parameters</name>
	<t>The receiver MUST ignore any parameter unspecified in this document.</t>	<t>This section specifies the optional parameters. A mapping of the parame
		ters with the Session Description Protocol (SDP) <xref target="RFC8866"/> is als
	<!-- Section 7.3.1 -->	o provided for applications that use SDP.</t>
		<t>Parameters starting with the string "sprop" for stream properties can b
	<section anchor="mapping-of-payload-type-parameters-to-sdp"><name>Mapping of Pay	e used by a sender to provide a receiver with the properties of the stream that
	load Type Parameters to SDP</name>	is or will be sent. The media sender (and not the receiver) selects whether, and
		with what values, "sprop" parameters are being sent. This uncommon characterist
	<t>The media type video/evc string is mapped to fields in the Session Descriptio	ic of the "sprop" parameters may not be intuitive in the context of some signali
	n Protocol (SDP) <xref target="RFC8866"/> as follows:</t>	ng protocol concepts, especially with Offer/Answer. Please see <xref target="sd
		poa"/> for guidance specific to the use of sprop parameters in the Offer/Answer
	<t><list style="symbols">	case.</t>
	<t>The media name in the "m=" line of SDP MUST be video.</t>
	<t>The encoding name in the "a=rtpmap" line of SDP MUST be evc (the
	media subtype).</t>
	<t>The clock rate in the "a=rtpmap" line MUST be 90000.</t>
	<t>The OPTIONAL parameters profile-id, level-id, toolset-id, max-recv-level-id
	, sprop-max-don-diff, sprop-depack-buf-bytes, and depack-buf-cap, when present,
	MUST be included in the "a=fmtp" line of SDP. The fmtp line is express
	ed as a media type string, in the form of a semicolon-separated list of paramete
	r=value pairs.</t>
	<t>The OPTIONAL parameters sprop-sps, sprop-pps, and sprop-sei, when present,
	MUST be included in the "a=fmtp" line of SDP or conveyed using the &qu
	ot;fmtp" source attribute as specified in Section 6.3 of <xref target="RFC5
	576"/>. For a particular media format (i.e., RTP payload type), sprop-sps, sprop
	-pps, or sprop-sei MUST NOT be both included in the "a=fmtp" line of S
	DP and conveyed using the "fmtp" source attribute. When included in th
	e "a=fmtp" line of SDP, those parameters are expressed as a media type
	string, in the form of a semicolon-separated list of parameter=value pairs. Whe
	n conveyed in the "a=fmtp" line of SDP for a particular payload type,
	the parameters sprop-sps, sprop-pps, and sprop-sei MUST be applied to each SSRC
	with the payload type. When conveyed using the "fmtp" source attribute
	, these parameters are only associated with the given source and payload type as
	parts of the "fmtp" source attribute.</t>
	</list></t>

	<ul empty="true"><li>
	<t>Informative note: Conveyance of sprop-sps and sprop-pps using the "fmt
	p" source attribute allows for out-of-band transport of parameter sets in t
	opologies like Topo-Video-switch-MCU, as specified in <xref target="RFC7667"/>.<
	/t>
	</li></ul>

	<t>A general usage of media representation in SDP is as follows:</t>

	<figure><artwork><![CDATA[
	m=video 49170 RTP/AVP 98
	a=rtpmap:98 evc/90000
	a=fmtp:98 profile-id=1;
	sprop-sps=<sequence parameter set data>;
	sprop-pps=<picture parameter set data>;
	]]></artwork></figure>


	<t>A SIP offer/answer exchange wherein both parties are expected to both send an	<section anchor="oparams">
	d receive could look like the following. Only the media codec-specific parts of	<name>Media Type Registration</name>
	the SDP are shown.</t>	<t>The receiver <bcp14>MUST</bcp14> ignore any parameter unspecified
		in this document.</t>
		<dl spacing="normal" newline="false">
		<dt>Type name:</dt><dd>video</dd>
		<dt>Subtype name:</dt><dd>evc</dd>
		<dt>Required parameters:</dt><dd>N/A</dd>
		<dt>Optional parameters:</dt><dd>profile-id, level-id, toolset-id,
		max-recv-level-id, sprop-sps, sprop-pps, sprop-sei,
		sprop-max-don-diff, sprop-depack-buf-bytes, depack-buf-cap (refer to
		<xref target="optionalParameters"/> for definitions)</dd>
		<dt>Encoding considerations:</dt> <dd>This type is only defined for
		transfer via RTP <xref target="RFC3550" format="default"/>.</dd>
		<dt>Security considerations:</dt> <dd>See <xref target="Security"/>
		of RFC 9584.</dd>
		<dt>Interoperability considerations:</dt><dd>N/A</dd>
		<dt>Published specification:</dt> <dd>Please refer to RFC 9584 and
		EVC standard <xref target="EVC"/>.</dd>
		<dt>Applications that use this media type:</dt> <dd>Any application
		that relies on EVC-based video services over RTP</dd>
		<dt>Fragment identifier considerations:</dt><dd>N/A</dd>
		<dt>Additional information:</dt><dd>N/A</dd>
		<dt>Person & email address to contact for further
		information:</dt> <dd><br/>Stephan Wenger (stewe@stewe.org)</dd>
		<dt>Intended usage:</dt><dd>COMMON</dd>
		<dt>Restrictions on usage:</dt><dd>N/A</dd>
		<dt>Author:</dt><dd>See Authors' Addresses section of RFC 9584.</dd>
		<dt>Change controller:</dt> <dd>IETF <avtcore@ietf.org></dd>
		</dl>
		</section>
		<section anchor="optionalParameters">
		<name>Optional Parameters Definition</name>
		<dl newline="true">
		<dt>profile-id, level-id, toolset-id:</dt>
		<dd><t>These parameters indicate the profile, the level, and
		constraints of the bitstream carried by the RTP stream or a
		specific set of the profile, the level, and constraints the receiver
		supports.</t>
		<t>More specifications of these parameters, including how they
		relate to syntax elements specified in <xref target="EVC"/> are
		provided below.</t>
		</dd>


	<figure><artwork><![CDATA[	<dt>profile-id:</dt>
	Offerer->Answerer:	<dd><t>When profile-id is not present, a value of 0 (i.e., the
	m=video 49170 RTP/AVP 98	Baseline profile) <bcp14>MUST</bcp14> be inferred.</t>
	a=rtpmap:98 evc/90000	<t>When used to indicate properties of a bitstream, profile-id
	a=fmtp:98 profile-id=1; level_id=90;	<bcp14>MUST</bcp14> be derived from the profile_idc in the SPS.</t>
		<t>EVC bitstreams transported over RTP using the technologies of
		this document <bcp14>SHOULD</bcp14> refer only to SPSs that have
		the same value in profile_idc, unless the sender has a priori
		knowledge that a receiver can correctly decode the EVC bitstream
		with different profile_idc values (for example, in walled garden
		scenarios). As exceptions to this rule, if the receiver is known
		to support a Baseline profile, a bitstream could safely end with CVS
		referring to an SPS wherein profile_idc indicates the Baseline
		Still picture profile. A similar exception can be made for Main
		profile and Main Still picture profile.</t>
		</dd>


	]]></artwork></figure>	<dt>level-id:</dt>
		<dd><t>When level-id is not present, a value of 90 (corresponding
		to level 3, which allows for approximately standard-definition
		television (SD TV) resolution and frame rates; see Annex A of <xref
		target="EVC"/>) <bcp14>MUST</bcp14> be inferred.</t>
		<t>When used to indicate properties of a bitstream, level-id
		<bcp14>MUST</bcp14> be derived from the level_idc in the SPS.</t>
		<t>If the level-id parameter is used for capability exchange, the
		following applies. If max-recv-level-id is not present, the default
		level defined by level-id indicates the highest level the codec
		wishes to support. Otherwise, max-recv-level-id indicates the
		highest level the codec supports for receiving. For either
		receiving or sending, all levels that are lower than the highest
		level supported <bcp14>MUST</bcp14> also be supported.</t>
		</dd>


	<ul empty="true"><li>	<dt>toolset-id:</dt>
	<t>The above represents an offer for symmetric video communication using <xref	<dd>This parameter is a base64-encoding representation (<xref
	target="EVC"/> and its payload specification at the main profile and level 3.0.	target="RFC4648" section="4" sectionFormat="of"/>) of a 64-bit
	Informally speaking, this offer tells the receiver of the offer that the sende	unsigned integer bit mask derived from the concatenation, in network
	r is willing to receive up to xKpxx resolution at the maximum bitrates specified	byte order, of the syntax elements toolset_idc_h and toolset_idc_l.
	in <xref target="EVC"/>. At the same time, if this offer were accepted "as	When used to indicate properties of a bitstream, its value
	is", the offer can expect that the answerer would be able to receive and p	<bcp14>MUST</bcp14> be derived from toolset_idh_h and toolset_idc_l in
	roperly decode EVC media up to and including level 3.0.</t>	the sequence parameter set.</dd>
	</li></ul>


	<figure><artwork><![CDATA[	<dt>max-recv-level-id:</dt>
	Answerer->Offerer:	<dd><t>This parameter <bcp14>MAY</bcp14> be used to indicate the
	m=video 49170 RTP/AVP 98	highest level a receiver supports.</t>
	a=rtpmap:98 evc/90000	<t>The value of max-recv-level-id <bcp14>MUST</bcp14> be in the range
	a=fmtp:98 profile-id=1; level_id=60	of 0 to 255, inclusive.</t>
	]]></artwork></figure>	<t>When max-recv-level-id is not present, the value is inferred to be
		equal to level-id.</t>
		<t>max-recv-level-id <bcp14>MUST NOT</bcp14> be present when the
		highest level the receiver supports is not higher than the default
		level.</t></dd>


	<ul empty="true"><li>	<dt>sprop-sps:</dt>
	<ul empty="true"><li>	<dd><t>This parameter <bcp14>MAY</bcp14> be used to convey sequence
	<t>Informative note: level_id shall be set equal to a value of 30 times the	parameter set NAL units of the bitstream for out-of-band transmission
	level number specified in Table A.1 of EVC.</t>	of sequence parameter sets. The value of the parameter is a
	</li></ul>	comma-separated (',') list of base64-encoding representations (<xref
	</li></ul>	target="RFC4648" section="4" sectionFormat="of"/>) of the sequence
		parameter set NAL units as specified in Section 7.3.2.1 of <xref
		target="EVC"/>.</t>
		</dd>


	<t>With this answer to the offer above, the system receiving the offer advises t	<dt>sprop-pps:</dt>
	he offerer that it is incapable of handing evc at level 3.0 but is capable of de	<dd><t>This parameter <bcp14>MAY</bcp14> be used to convey picture
	coding level 2. As EVC video codecs must support decoding at all levels below th	parameter set NAL units of the bitstream for out-of-band transmission
	e maximum level they implement, the resulting user experience would likely be th	of picture parameter sets. The value of the parameter is a
	at both systems send video at level 2. However, nothing prevents an encoder from	comma-separated (',') list of base64-encoding representations (<xref
	further downgrading its sending to, for example, level 1 if it were short of cy	target="RFC4648" section="4" sectionFormat="of"/>) of the picture
	cles or bandwidth or for other reasons.</t>	parameter set NAL units as specified in Section 7.3.2.2 of <xref
		target="EVC"/>.</t></dd>


	<!-- Section 7.3.2 -->	<dt>sprop-sei:</dt>
		<dd><t>This parameter <bcp14>MAY</bcp14> be used to convey one or more
		SEI messages that describe bitstream characteristics. When present, a
		decoder can rely on the bitstream characteristics that are described
		in the SEI messages for the entire duration of the session,
		independently from the persistence scopes of the SEI messages as
		specified in <xref target="VSEI"/>.</t>
		<t>The value of the parameter is a comma-separated (',') list of
		base64-encoding representations (<xref target="RFC4648" section="4"
		sectionFormat="of"/>) of SEI NAL units as specified in
		<xref target="VSEI"/>.</t>
		<aside><t>Informative note: Intentionally, no list of
		applicable or inapplicable SEI messages is specified here.
		Conveying certain SEI messages in sprop-sei may be sensible in
		some application scenarios and meaningless in others. However,
		a couple of examples are described below.</t>
		<ol type="1">
		<li>In an environment where the bitstream was created from
		film-based source material, and no splicing is going to occur
		during the lifetime of the session, the film grain
		characteristics SEI message is likely meaningful; and sending
		it in sprop-sei rather than in the bitstream at each entry
		point may help with saving bits and allow one to configure
		the renderer only once, avoiding unwanted artifacts.</li>
		<li>Examples for SEI messages that would be meaningless to be
		conveyed in sprop-sei include the decoded picture hash SEI
		message (it is close to impossible that all decoded pictures
		have the same hashtag) or the filler payload SEI message (as
		there is no point in just having more bits in SDP).</li>
		</ol></aside>
		</dd>


	</section>	<dt>sprop-max-don-diff:</dt>
	<section anchor="sdpoa"><name>Usage with SDP Offer/Answer Model</name>


	<t>This section describes the negotiation of unicast messages using the offer/an swer model described in <xref target="RFC3264"/> and its updates.</t>	<dd><t>If there is no NAL unit naluA that is followed in transmission order by any NAL unit preceding naluA in decoding order (i.e., the transmission order of the NAL units is the same as the decoding order), the value of this pa rameter <bcp14>MUST</bcp14> be equal to 0.</t>


	<t>This section applies to all profiles defined in <xref target="EVC"/>, specifi cally to Baseline, Main, and the associated still image profiles.</t>	<t>Otherwise, this parameter specifies the maximum absolute differen ce between the decoding order number (i.e., AbsDon) values of any two NAL units naluA and naluB, where naluA follows naluB in decoding order and precedes naluB in transmission order.</t>


	<t>The following limitations and rules pertaining to the media configuration app ly:</t>	<t>The value of sprop-max-don-diff <bcp14>MUST</bcp14> be an integer in the range of 0 to 32767, inclusive.</t>


	<t>The parameters identifying a media format configuration for EVC are profile-i	<t>When not present, the value of sprop-max-don-diff is inferred to
	d and level-id. Profile_id MUST be used symmetrically.</t>	be equal to 0.</t>
		</dd>


	<t>The answerer MUST structure its answer according to one of the following thre	<dt>sprop-depack-buf-bytes:</dt>
	e options:</t>	<dd>


	<ul empty="true"><li>	<t>This parameter signals the required size of the de-packetization
	<t><list style="symbols">	buffer in units of bytes. The value of the parameter <bcp14>MUST</bcp14> be gre
	<t>maintain all configuration parameters with the values remaining the same	ater than or equal to the maximum buffer occupancy (in units of bytes) of the de
	as in the offer for the media format (payload type), with the exception that the	-packetization buffer as specified in <xref target="DepacketizationProcess" form
	value of level-id is changeable as long as the highest level indicated by the a	at="default"/>.</t>
	nswer is not higher than that indicated by the offer; or</t>
	</list></t>
	</li></ul>


	<ul empty="true"><li>	<t>The value of sprop-depack-buf-bytes <bcp14>MUST</bcp14> be an int
	<t><list style="symbols">	eger in the range of 0 to 4294967295, inclusive.</t>
	<t>remove the media format (payload type) completely (when one or more of th
	e parameter values are not supported).</t>
	</list></t>
	</li></ul>


	<t>Informative note: The above requirement for symmetric use does not apply for level-id and does not apply for the other bitstream or RTP stream properties and capability parameters, as described in <xref target="formatconfig"/> (Payload f ormat config) below.</t>	<t>When sprop-max-don-diff is present and greater than 0, this param eter <bcp14>MUST</bcp14> be present and the value <bcp14>MUST</bcp14> be greater than 0. When not present, the value of sprop-depack-buf-bytes is inferred to b e equal to 0.</t>


	<t>To simplify handling and matching of these configurations, the same RTP paylo	<aside><t>Informative note: The value of
	ad type number used in the offer SHOULD also be used in the answer, as specified	sprop-depack-buf-bytes indicates the required size of the
	in <xref target="RFC3264"></xref>.</t>	de-packetization buffer only. When network jitter can occur, an
		appropriately sized jitter buffer has to be available as
		well.</t></aside>
		</dd>


	<t>The answer MUST NOT contain a payload type number used in the offer for the m	<dt>depack-buf-cap:</dt>
	edia subtype unless the configuration is the same as in the offer or the configu	<dd>
	ration in the answer only differs from that in the offer with a different value	<t>This parameter signals the capabilities of a receiver
	of level-id.</t>	implementation and indicates the amount of de-packetization buffer
		space in units of bytes that the receiver has available for
		reconstructing the NAL unit decoding order from NAL units carried in
		the RTP stream. A receiver is able to handle any RTP stream for
		which the value of the sprop-depack-buf-bytes parameter is smaller
		than or equal to this parameter.</t>
		<t>When not present, the value of depack-buf-cap is inferred to be
		equal to 4294967295. The value of depack-buf-cap
		<bcp14>MUST</bcp14> be an integer in the range of 1 to 4294967295,
		inclusive.</t>


	<!-- Section 7.3.2.x -->	<aside><t>Informative note: The value of depack-buf-cap indicates
		the maximum possible size of the de-packetization buffer of the
		receiver only, without allowing for network jitter. When network
		jitter occurs, an appropriately sized jitter buffer has to be
		available as well. </t></aside>
		</dd>
		</dl>


	<section anchor="formatconfig"><name>Payload Format Configuration</name>	</section>


	<t>The following limitations and rules pertain to the configuration of the paylo	<section anchor="sdp-parameters">
	ad format buffer management.</t>	<name>SDP Parameters</name>
		<t>The receiver <bcp14>MUST</bcp14> ignore any parameter unspecified in
		this document.</t>


	<t>The parameters sprop-max-don-diff and sprop-depack-buf-bytes describe the pro	<section anchor="mapping-of-payload-type-parameters-to-sdp">
	perties of an RTP stream that the offerer or the answerer is sending for the med	<name>Mapping of Payload Type Parameters to SDP</name>
	ia format configuration. This differs from the normal usage of the offer/answer	<t>The media type video/evc string is mapped to fields in the Session
	parameters; normally, such parameters declare the properties of the bitstream or	Description Protocol (SDP) <xref target="RFC8866"/> as follows:</t>
	RTP stream that the offerer or the answerer is able to receive. When dealing wi	<ul spacing="normal">
	th EVC, the offerer assumes that the answerer will be able to receive media enco	<li>The media name in the "m=" line of SDP <bcp14>MUST</bcp14>
	ded using the configuration being offered.</t>	be video.</li>
		<li>The encoding name in the "a=rtpmap" line of SDP
		<bcp14>MUST</bcp14> be evc (the media subtype).</li>
		<li>The clock rate in the "a=rtpmap" line <bcp14>MUST</bcp14> be
		90000.</li>


	<t>Informative note: The above parameters apply for any RTP stream, when present	<li>The <bcp14>OPTIONAL</bcp14> parameters profile-id, level-id,
	, sent by a declaring entity with the same configuration. In other words, the ap	toolset-id, max-recv-level-id, sprop-max-don-diff,
	plicability of the above parameters to RTP streams depends on the source endpoin	sprop-depack-buf-bytes, and depack-buf-cap, when present,
	t. Rather than being bound to the payload type, the values may have to be applie	<bcp14>MUST</bcp14> be included in the "a=fmtp" line of SDP. The
	d to another payload type when being sent, as they apply for the configuration.<	"a=fmtp" line is expressed as a media type string, in the form of a
	/t>	semicolon-separated list of parameter=value pairs.</li>
		<li>The <bcp14>OPTIONAL</bcp14> parameters sprop-sps, sprop-pps,
		and sprop-sei, when present, <bcp14>MUST</bcp14> be included in
		the "a=fmtp" line of SDP or conveyed using the "fmtp" source
		attribute as specified in <xref target="RFC5576"
		sectionFormat="of" section="6.3"/>. For a particular media format
		(i.e., RTP payload type), sprop-sps, sprop-pps, or sprop-sei
		<bcp14>MUST NOT</bcp14> be both included in the "a=fmtp" line of
		SDP and conveyed using the "fmtp" source attribute. When included
		in the "a=fmtp" line of SDP, those parameters are expressed as a
		media type string, in the form of a semicolon-separated list
		of parameter=value pairs. When conveyed in the "a=fmtp" line of
		SDP for a particular payload type, the parameters sprop-sps,
		sprop-pps, and sprop-sei <bcp14>MUST</bcp14> be applied to each
		SSRC with the payload type. When conveyed using the "fmtp" source
		attribute, these parameters are only associated with the given
		source and payload type as parts of the "fmtp" source
		attribute.</li>
		</ul>
		<aside><t>Informative note: Conveyance of sprop-sps and sprop-pps
		using the "fmtp" source attribute allows for out-of-band transport
		of parameter sets in topologies like Topo-Video-switch-MCU, as
		specified in <xref target="RFC7667"/>.</t></aside>


	<t>When an offerer offers an interleaved stream, indicated by the presence of sp rop-max-don-diff with a value larger than zero, the offerer MUST include the siz e of the de-packetization buffer sprop-depack-buf-bytes.</t>	<t>A general usage of media representation in SDP is as follows:</t>


	<t>To enable the offerer and answerer to inform each other about their capabilit	<artwork><![CDATA[
	ies for de-packetization buffering in receiving RTP streams, both parties are RE	m=video 49170 RTP/AVP 98
	COMMENDED to include depack-buf-cap.</t>	a=rtpmap:98 evc/90000
		a=fmtp:98 profile-id=1;
		sprop-sps=<sequence parameter set data>;
		sprop-pps=<picture parameter set data>;
		]]></artwork>


	<t>The parameters sprop-sps, or sprop-pps, when present (included in the "a	<t>A SIP Offer/Answer exchange wherein both parties are expected to
	=fmtp" line of SDP or conveyed using the "fmtp" source attribute,	both send and receive could look like the following. Only the media
	as specified in Section 6.3 of <xref target="RFC5576"></xref>), are used for ou	codec-specific parts of the SDP are shown.</t>
	t-of-band transport of the parameter sets (SPS or PPS, respectively).
	The answerer MAY use either out-of-band or in-band transport of parameter sets f
	or the bitstream it is sending, regardless of whether out-of-band parameter sets
	transport has been used in the offerer-to-answerer direction. Parameter sets in
	cluded in an answer are independent of those parameter sets included in the offe
	r, as they are used for decoding two different bitstreams; one from the answerer
	to the offerer and the other in the opposite direction. In case some RTP packet
	s are sent before the SDP offer/answer settles down, in-band parameter sets MUST
	be used for those RTP stream parts sent before the SDP offer/answer.</t>


	<t>The following rules apply to transport of parameter sets in the offerer-to-an	<artwork><![CDATA[
	swerer direction.</t>	Offerer->Answerer:
		m=video 49170 RTP/AVP 98
		a=rtpmap:98 evc/90000
		a=fmtp:98 profile-id=1; level_id=90;
		]]></artwork>


	<t>An offer MAY include sprop-sps, and/or sprop-pps. If none of these parameters	<t>The above represents an offer for symmetric video communication
	are present in the offer, then only in-band transport of parameter sets is used	using <xref target="EVC"/> and its payload specification at the main
	.</t>	profile and level 3. Informally speaking, this offer tells the
		receiver of the offer that the sender is willing to receive up to
		xKpxx resolution at the maximum bitrates specified in <xref
		target="EVC"/>. At the same time, if this offer were accepted "as
		is", the offer can expect that the Answerer would be able to receive
		and properly decode EVC media up to and including level 3.</t>


	<t>If the level to use in the offerer-to-answerer direction is equal to the defa	<artwork><![CDATA[
	ult level in the offer, the answerer MUST be prepared to use the parameter sets	Answerer->Offerer:
	included in sprop-sps, and sprop-pps (either included in the "a=fmtp"	m=video 49170 RTP/AVP 98
	line of SDP or conveyed using the "fmtp" source attribute) for decodin	a=rtpmap:98 evc/90000
	g the incoming bitstream, e.g., by passing these parameter set NAL units to the	a=fmtp:98 profile-id=1; level_id=60
	video decoder before passing any NAL units carried in the RTP streams. Otherwise	]]></artwork>
	, the answerer MUST ignore sprop-vps, sprop-sps, and sprop-pps (either included
	in the "a=fmtp" line of SDP or conveyed using the "fmtp" sou
	rce attribute) and the offerer MUST transmit parameter sets in-band.</t>


	<t>The following rules apply to transport of parameter sets in the answerer-to-o	<aside><t>Informative note: level_id shall be set equal to a
	fferer direction.</t>	value of 30 times the level number specified in Table A.1 of
		<xref target="EVC"/>.</t></aside>


	<t>An answer MAY include sprop-sps, and/or sprop-pps. If none of these parameter	<t>With this answer to the offer above, the system receiving the
	s are present in the answer, then only in-band transport of parameter sets is us	offer advises the Offerer that it is incapable of handling evc at
	ed.</t>	level 3 but is capable of decoding level 2. As EVC video codecs
		must support decoding at all levels below the maximum level they
		implement, the resulting user experience would likely be that both
		systems send video at level 2. However, nothing prevents an encoder
		from further downgrading its sending to, for example, level 1 if it
		were short of cycles or bandwidth or for other reasons.</t>
		</section>
		<section anchor="sdpoa">
		<name>Usage with SDP Offer/Answer Model</name>
		<t>This section describes the negotiation of unicast messages using th
		e Offer/Answer model described in <xref target="RFC3264"/> and its updates.</t>
		<t>This section applies to all profiles defined in <xref target="EVC"/
		>, specifically to Baseline, Main, and the associated still image profiles.</t>
		<t>The following limitations and rules pertaining to the media configu
		ration apply:</t>
		<t>The parameters identifying a media format configuration for EVC are
		profile-id and level-id. Profile_id <bcp14>MUST</bcp14> be used symmetrically.<
		/t>


	<t>The offerer MUST be prepared to use the parameter sets included in sprop-sps	<t>The Answerer <bcp14>MUST</bcp14> structure its answer according to
	and sprop-pps (either included in the "a=fmtp" line of SDP or conveyed	one of the following two options:</t>
	using the "fmtp" source attribute) for decoding the incoming bitstrea	<ul spacing="normal">
	m, e.g., by passing these parameter set NAL units to the video decoder before pa	<li>maintain all configuration parameters with the values
	ssing any NAL units carried in the RTP streams.</t>	remaining the same as in the offer for the media format (payload
		type), with the exception that the value of level-id is changeable
		as long as the highest level indicated by the answer is not higher
		than that indicated by the offer; or</li>
		<li>remove the media format (payload type) completely (when one or
		more of the parameter values are not supported).</li>
		</ul>


	<t>When sprop-sps and/or sprop-pps are conveyed using the "fmtp" sourc	<aside><t>Informative note: The above requirement for symmetric use do
	e attribute, as specified in Section 6.3 of <xref target="RFC5576"></xref>, the	es not apply for level-id and does not apply for the other bitstream or RTP stre
	receiver of the parameters MUST store the parameter sets included in sprop-sps a	am properties and capability parameters, as described in <xref target="formatcon
	nd/or sprop-pps and associate them with the source given as part of the "fm	fig"/> ("<xref target="formatconfig" format="title"/>").</t></aside>
	tp" source attribute. Parameter sets associated with one source (given as p	<t>To simplify handling and matching of these configurations, the same
	art of the "fmtp" source attribute) MUST only be used to decode NAL un	RTP payload type number used in the offer <bcp14>SHOULD</bcp14> also be used in
	its conveyed in RTP packets from the same source (given as part of the "fmt	the answer, as specified in <xref target="RFC3264"/>.</t>
	p" source attribute). When this mechanism is in use, SSRC collision detecti	<t>The answer <bcp14>MUST NOT</bcp14> contain a payload type number us
	on and resolution MUST be performed as specified in <xref target="RFC5576"></xre	ed in the offer for the media subtype unless the configuration is the same as in
	f>.</t>	the offer or the configuration in the answer only differs from that in the offe
		r with a different value of level-id.</t>


	<t><xref target="params-interpretation"/> lists the interpretation of all the pa	<section anchor="formatconfig">
	rameters that MAY be used for the various combinations of offer, answer, and dir	<name>Payload Format Configuration</name>
	ection attributes.</t>	<t>The following limitations and rules pertain to the configuration
		of the payload format buffer management.</t>
		<ul spacing="normal">
		<li><t>The parameters sprop-max-don-diff and sprop-depack-buf-byte
		s describe the properties of an RTP stream that the Offerer or the Answerer is s
		ending for the media format configuration. This differs from the normal usage of
		the Offer/Answer parameters; normally, such parameters declare the properties o
		f the bitstream or RTP stream that the Offerer or the Answerer is able to receiv
		e. When dealing with EVC, the Offerer assumes that the Answerer will be able to
		receive media encoded using the configuration being offered.</t></li>
		</ul>
		<aside><t>Informative note: The above parameters apply for any RTP s
		tream, when present, sent by a declaring entity with the same configuration. In
		other words, the applicability of the above parameters to RTP streams depends on
		the source endpoint. Rather than being bound to the payload type, the values ma
		y have to be applied to another payload type when being sent, as they apply for
		the configuration.</t></aside>
		<ul spacing="normal">
		<li><t>When an Offerer offers an interleaved stream, indicated
		by the presence of sprop-max-don-diff with a value larger than
		zero, the Offerer <bcp14>MUST</bcp14> include the size of the
		de-packetization buffer sprop-depack-buf-bytes.</t></li>
		<li><t>To enable the Offerer and Answerer to inform each other
		about their capabilities for de-packetization buffering in
		receiving RTP streams, both parties are
		<bcp14>RECOMMENDED</bcp14> to include depack-buf-cap.</t></li>
		<li><t>The parameters sprop-sps or sprop-pps, when present
		(included in the "a=fmtp" line of SDP or conveyed using the
		"fmtp" source attribute, as specified in <xref target="RFC5576"
		sectionFormat="of" section="6.3"/>), are used for out-of-band
		transport of the parameter sets (SPS or PPS, respectively). The
		Answerer <bcp14>MAY</bcp14> use either out-of-band or in-band
		transport of parameter sets for the bitstream it is sending,
		regardless of whether out-of-band parameter sets transport has
		been used in the Offerer-to-Answerer direction. Parameter sets
		included in an answer are independent of those parameter sets
		included in the offer, as they are used for decoding two
		different bitstreams: one from the Answerer to the Offerer, and
		the other in the opposite direction. In case some RTP packets
		are sent before the SDP Offer/Answer settles down, in-band
		parameter sets <bcp14>MUST</bcp14> be used for those RTP stream
		parts sent before the SDP Offer/Answer.</t></li>
		<li><t>The following rules apply to transport of parameter sets
		in the Offerer-to-Answerer direction.</t>
		<ul spacing="normal">
		<li><t>An offer <bcp14>MAY</bcp14> include sprop-sps and/or
		sprop-pps. If none of these parameters are present in the
		offer, then only in-band transport of parameter sets is
		used.</t></li>
		<li><t>If the level to use in the Offerer-to-Answerer
		direction is equal to the default level in the offer, the
		Answerer <bcp14>MUST</bcp14> be prepared to use the parameter
		sets included in sprop-sps and sprop-pps (either included in
		the "a=fmtp" line of SDP or conveyed using the "fmtp" source
		attribute) for decoding the incoming bitstream, e.g., by
		passing these parameter set NAL units to the video decoder
		before passing any NAL units carried in the RTP
		streams. Otherwise, the Answerer <bcp14>MUST</bcp14> ignore
		sprop-vps, sprop-sps, and sprop-pps (either included in the
		"a=fmtp" line of SDP or conveyed using the "fmtp" source
		attribute), and the Offerer <bcp14>MUST</bcp14> transmit
		parameter sets in-band.</t></li>
		</ul></li>
		<li><t>The following rules apply to transport of parameter sets in
		the Answerer-to-Offerer direction.</t>
		<ul spacing="normal">
		<li><t>An answer <bcp14>MAY</bcp14> include sprop-sps and/or
		sprop-pps. If none of these parameters are present in the
		answer, then only in-band transport of parameter sets is
		used.</t></li>
		<li><t>The Offerer <bcp14>MUST</bcp14> be prepared to use the
		parameter sets included in sprop-sps and sprop-pps (either
		included in the "a=fmtp" line of SDP or conveyed using the
		"fmtp" source attribute) for decoding the incoming bitstream,
		e.g., by passing these parameter set NAL units to the video
		decoder before passing any NAL units carried in the RTP
		streams.</t></li>
		</ul></li>
		<li><t>When sprop-sps and/or sprop-pps are conveyed using the
		"fmtp" source attribute, as specified in <xref target="RFC5576"
		sectionFormat="of" section="6.3"/>, the receiver of the parameters
		<bcp14>MUST</bcp14> store the parameter sets included in sprop-sps
		and/or sprop-pps and associate them with the source given as part
		of the "fmtp" source attribute. Parameter sets associated with one
		source (given as part of the "fmtp" source attribute)
		<bcp14>MUST</bcp14> only be used to decode NAL units conveyed in
		RTP packets from the same source (given as part of the "fmtp"
		source attribute). When this mechanism is in use, SSRC collision
		detection and resolution <bcp14>MUST</bcp14> be performed as
		specified in <xref target="RFC5576"/>.</t></li>
		</ul>
		<t><xref target="params-interpretation"/> lists the interpretation o
		f all the parameters that <bcp14>MAY</bcp14> be used for the various combination
		s of offer, answer, and direction attributes.</t>


	<figure anchor="params-interpretation"><artwork><![CDATA[	<figure anchor="params-interpretation">
		<name>Interpretation of Parameters for Various Combinations of
		Offers, Answers, and Direction Attributes</name>
		<artwork><![CDATA[
	sendonly --+	sendonly --+
	recvonly --+ \|	recvonly --+ \|
	sendrecv --+ \| \|	sendrecv --+ \| \|
	\| \| \|	\| \| \|
	profile-id C C P	profile-id C C P
	level-id D D P	level-id D D P
	toolset-id C C P	toolset-id C C P
	max-recv-level-id R R -	max-recv-level-id R R -
	sprop-max-don-diff P - P	sprop-max-don-diff P - P
	sprop-depack-buf-bytes P - P	sprop-depack-buf-bytes P - P
	depack-buf-cap R R -	depack-buf-cap R R -
	sprop-sei P - P	sprop-sei P - P
	sprop-sps P - P	sprop-sps P - P
	sprop-pps P - P	sprop-pps P - P

	Legend:	Legend:

	C: configuration for sending and receiving bitstreams	C: configuration for sending and receiving bitstreams

	D: changeable configuration, same as C, except possible to	D: changeable configuration; same as C, except possible to
	answer with a different but consistent value (see the semantics	answer with a different but consistent value (see the semantics
	of the level-id parameter on these parameters being	of the level-id parameter on these parameters being

	consistent-basically, level down-grading is allowed)	consistent -- basically, level down-grading is allowed)

	P: properties of the bitstream to be sent	P: properties of the bitstream to be sent
	R: receiver capabilities	R: receiver capabilities

	-: not usable, when present MUST be ignored	-: not usable; when present MUST be ignored]]></artwork>
		</figure>
	Interpretation of Parameters for Various Combinations of
	Offers, Answers, and Direction Attributes.

	]]></artwork></figure>

	<t>Parameters used for declaring receiver capabilities are, in general, downgrad
	able, i.e., they express the upper limit for a sender's possible behavior. T
	hus, a sender MAY select to set its encoder using only lower/lesser or equal val
	ues of these parameters.</t>

	<t>When a sender's capabilities are declared with the configuration paramete
	rs, these parameters express a configuration that is acceptable for the sender t
	o receive bitstreams. In order to achieve high interoperability levels, it is of
	ten advisable to offer multiple alternative configurations. It is impossible to
	offer multiple configurations in a single payload type. Thus, when multiple conf
	iguration offers are made, each offer requires its own RTP payload type associat
	ed with the offer.</t>

	<t>An implementation SHOULD be able to understand all media type parameters (inc
	luding all optional media type parameters), even if it doesn't support the f
	unctionality related to the parameter. This, in conjunction with proper applicat
	ion logic in the implementation, allows the implementation, after having receive
	d an offer, to create an answer by potentially downgrading one or more of the op
	tional parameters to the point where the implementation can cope, leading to hig
	her chances of interoperability beyond the most basic interop points (for which,
	as described above, no optional parameters are necessary).</t>

	<t>Informative note: In implementations of various H.26x video coding payload Fo
	rmats including those for <xref target="AVC"/> and <xref target="HEVC"/>, it was
	occasionally observed that implementations were incapable of parsing most (or a
	ll) of the optional parameters and hence rejected offers other than the most bas
	ic offers. As a result, the offer/answer exchange resulted in a baseline perform
	ance (using the default values for the optional parameters) with the resulting s
	uboptimal user experience. However, there are valid reasons to forego the implem
	entation complexity of implementing the parsing of some or all of the optional p
	arameters, for example, when there is predetermined knowledge, not negotiated by
	an SDP-based offer/answer process, of the capabilities of the involved systems
	(walled gardens, baseline requirements defined in application standards higher u
	p in the stack, and similar).</t>

	<t>An answerer MAY extend the offer with additional media format configurations.
	However, to enable their usage, in most cases, a second offer is required from
	the offerer to provide the bitstream property parameters that the media sender w
	ill use. This also has the effect that the offerer has to be able to receive thi
	s media format configuration, not only to send it.</t>

	</section>
	</section>
	<section anchor="multicast"><name>Multicast</name>

	<t>For bitstreams being delivered over multicast, the following rules apply:</t>

	<t>The media format configuration is identified by profile-id and level-id. Thes
	e media format configuration parameters, including level-id, MUST be used symmet
	rically; that is, the answerer MUST either maintain all configuration parameters
	or remove the media format (payload type) completely. Note that this implies th
	at the level-id for offer/answer in multicast is not changeable.</t>

	<t>To simplify the handling and matching of these configurations, the same RTP p
	ayload type number used in the offer SHOULD also be used in the answer, as speci
	fied in <xref target="RFC3264"></xref>. An answer MUST NOT contain a payload typ
	e number used in the offer unless the configuration is the same as in the offer.
	</t>

	<t>Parameter sets received MUST be associated with the originating source and MU
	ST only be used in decoding the incoming bitstream from the same source.</t>

	<t>The rules for other parameters are the same as above for unicast as long as t
	he three above rules are obeyed.</t>

	</section>
	<section anchor="declativeSessiondesc"><name>Usage in Declarative Session Descri
	ptions</name>

	<t>When EVC over RTP is offered with SDP in a declarative style, as in Real Time
	Streaming Protocol (RTSP) <xref target="RFC7826"></xref> or Session Announcemen
	t Protocol (SAP) <xref target="RFC2974"></xref>, the following considerations ap
	ply.</t>

	<t>All parameters capable of indicating both bitstream properties and receiver c
	apabilities are used to indicate only bitstream properties. For example, in this
	case, the parameters profile-id and level-id declare the values used by the bit
	stream, not the capabilities for receiving bitstreams. As a result, the followin
	g interpretation of the parameters MUST be used:</t>

	<t>Declaring actual configuration or bitstream properties:</t>

	<t>profile-id
	level-id
	sprop-sps
	sprop-pps
	sprop-max-don-diff
	sprop-depack-buf-bytes
	sprop-sei</t>

	<t>Not usable (when present, they MUST be ignored):</t>

	<t>depack-buf-cap
	recv-sublayer-id</t>

	<t>A receiver of the SDP is required to support all parameters and values of the
	parameters provided; otherwise, the receiver MUST reject (RTSP) or not particip
	ate in (SAP) the session. It falls on the creator of the session to use values t
	hat are expected to be supported by the receiving application.</t>

	</section>
	<section anchor="consider4pps"><name>Considerations for Parameter Sets</name>

	<t>When out-of-band transport of parameter sets is used, parameter sets MAY stil
	l be additionally transported in-band unless explicitly disallowed by an applica
	tion, and some of these additional parameter sets may update some of the out-of-
	band transported parameter sets. An update of a parameter set refers to the send
	ing of a parameter set of the same type using the same parameter set ID but with
	different values for at least one other parameter of the parameter set.</t>

	<!-- Section 8 -->

	</section>
	</section>
	</section>
	<section anchor="FeedbackMessage"><name>Use with Feedback Messages</name>

	<t>The following subsections define the use of the Picture Loss Indication (PLI)
	and Full Intra Request (FIR) feedback messages with <xref target="EVC"/>. The P
	LI is defined in <xref target="RFC4585"/>, and the FIR message is defined in <xr
	ef target="RFC5104"/>.</t>

	<t>In accordance with this document, a sender MUST NOT send Slice Loss Indicatio
	n (SLI) or Reference Picture Selection Indication (RPSI), and a receiver MUST ig
	nore RPSI and MUST treat a received SLI as a received PLI, ignoring the "Fi
	rst", "Number", and "PictureID" fields of the PLI.</t>

	<!-- Section 8.1 -->

	<section anchor="PLI"><name>Picture Loss Indication (PLI)</name>

	<t>As specified in Section 6.3.1 of <xref target="RFC4585"/>, the reception of a
	PLI by a media sender indicates "the loss of an undefined amount of coded
	video data belonging to one or more pictures". Without having any specific
	knowledge of the setup of the bitstream (such as use and location of in-band par
	ameter sets, IDR picture locations, picture structures, and so forth), a reactio
	n to the reception of a PLI by a EVC sender SHOULD be to send an IDR picture and
	relevant parameter sets, potentially with sufficient redundancy so to ensure co
	rrect reception. However, sometimes information about the bitstream structure is
	known. For example, such information can be parameter sets that have been conve
	yed out of band through mechanisms not defined in this document and that are kno
	wn to stay static for the duration of the session. In that case, it is obviously
	unnecessary to send them in-band as a result of the reception of a PLI. Other e
	xamples could be devised based on a priori knowledge of different aspects of the
	bitstream structure. In all cases, the timing and congestion control mechanisms
	of <xref target="RFC4585"/> MUST be observed.</t>

	<!-- Section 8.2 -->

	</section>
	<section anchor="FIR"><name>Full Intra Request (FIR)</name>

	<t>The purpose of the FIR message is to force an encoder to send an independent
	decoder refresh point as soon as possible while observing applicable congestion-
	control-related constraints, such as those set out in <xref target="RFC8082"/>.<
	/t>

	<t>Upon reception of a FIR, a sender MUST send an IDR picture. Parameter sets MU
	ST also be sent, except when there is a priori knowledge that the parameter sets
	have been correctly established. A typical example for that is an understanding
	between the sender and receiver, established by means outside this document, th
	at parameter sets are exclusively sent out of band.</t>

	</section>
	</section>
	<section anchor="Security"><name>Security Considerations</name>

	<t>The scope of this section is limited to the payload format itself and to one
	feature of <xref target="EVC"/> that may pose a particularly serious security ri
	sk if implemented naively. The payload format, in isolation, does not form a com
	plete system. Implementers are advised to read and understand relevant security-
	related documents, especially those pertaining to RTP (see the Security Consider
	ations section in <xref target="RFC3550"/>) and the security of the call-control
	stack chosen (that may make use of the media type registration of this document
	). Implementers should also consider known security vulnerabilities of video cod
	ing and decoding implementations in general and avoid those.</t>

	<t>Within this RTP payload format, and with the exception of the user data SEI m
	essage as described below, no security threats other than those common to RTP pa
	yload formats are known. In other words, neither the various media-plane-based m
	echanisms nor the signaling part of this document seem to pose a security risk b
	eyond those common to all RTP-based systems.</t>

	<t>RTP packets using the payload format defined in this specification are subjec
	t to the security considerations discussed in the RTP specification <xref target
	="RFC3550"/>, and in any applicable RTP profile such as RTP/AVP <xref target="RF
	C3551"/>, RTP/AVPF <xref target="RFC4585"/>, RTP/SAVP <xref target="RFC3711"/>,
	or RTP/SAVPF <xref target="RFC5124"/>. However, as "Securing the RTP Frame
	work: Why RTP Does Not Mandate a Single Media Security Solution" <xref targ
	et="RFC7202"/> discusses, it is not an RTP payload format's responsibility t
	o discuss or mandate what solutions are used to meet the basic security goals li
	ke confidentiality, integrity and source authenticity for RTP in general. This
	responsibility lays on anyone using RTP in an application. They can find guidan
	ce on available security mechanisms and important considerations in "Option
	s for Securing RTP Sessions" <xref target="RFC7201"/>. Applications SHOULD
	use one or more appropriate strong security mechanisms. The rest of this sectio
	n discusses the security impacting properties of the payload format itself.</t>

	<t>Because the data compression used with this payload format is applied end-to-
	end, any encryption needs to be performed after compression. A potential denial-
	of-service threat exists for data encodings using compression techniques that ha
	ve non-uniform receiver-end computational load. The attacker can inject patholo
	gical datagrams into the bitstream that are complex to decode and that cause the
	receiver to be overloaded.</t>

	<t>EVC is particularly vulnerable to such attacks, as it is extremely simple to
	generate datagrams containing NAL units that affect the decoding process of many
	future NAL units. Therefore, the usage of data origin authentication and data i
	ntegrity protection of at least the RTP packet is RECOMMENDED based on the thoug
	hts of <xref target="RFC7202"/>.</t>

	<t>Like HEVC <xref target="RFC7798"/> and <xref target="VVC"/>, <xref target="EV
	C"/> includes a user data Supplemental Enhancement Information (SEI) message. Th
	is SEI message allows inclusion of an arbitrary bitstring into the video bitstre
	am. Such a bitstring could include JavaScript, machine code, and other active co
	ntent.</t>

	<t><xref target="EVC"></xref> leaves the handling of this SEI message to the rec
	eiving system. In order to avoid harmful side effects of the user data SEI messa
	ge, decoder implementations cannot naively trust its content. For example, forwa
	rding all received JavaScript code detected by a decoder implementation to a web
	-browser unchecked would be a bad and insecure implementation practice. The safe
	st way to deal with user data SEI messages is to simply discard them, but that c
	an have negative side effects on the quality of experience by the user.</t>

	<t>End-to-end security with authentication, integrity, or confidentiality protec
	tion will prevent a MANE from performing media-aware operations other than disca
	rding complete packets. In the case of confidentiality protection, it will even
	be prevented from discarding packets in a media-aware way. To be allowed to pe
	rform such operations, a MANE is required to be a trusted entity that is include
	d in the security context establishment.</t>

	</section>
	<section anchor="CC"><name>Congestion Control</name>

	<t>Congestion control for RTP SHALL be used in accordance with RTP <xref target=
	"RFC3550"/> and with any applicable RTP profile, e.g., AVP <xref target="RFC3551
	"/> or AVPF <xref target="RFC4585"/>. If best-effort service is being used, an a
	dditional requirement is that users of this payload format MUST monitor packet l
	oss to ensure that the packet loss rate is within an acceptable range. Packet lo
	ss is considered acceptable if a TCP flow across the same network path and exper
	iencing the same network conditions would achieve an average throughput, measure
	d on a reasonable timescale, that is not less than all RTP streams combined are
	achieved. This condition can be satisfied by implementing congestion-control mec
	hanisms to adapt the transmission rate, by implementing the number of layers sub
	scribed for a layered multicast session, or by arranging for a receiver to leave
	the session if the loss rate is unacceptably high.</t>

	<t>The bitrate adaptation necessary for obeying the congestion control principle
	is easily achievable when real-time encoding is used, for example, by adequatel
	y tuning the quantization parameter. However, when pre-encoded content is being
	transmitted, bandwidth adaptation requires the pre-coded bitstream to be tailore
	d for such adaptivity.</t>

	<t>The key mechanism available in <xref target="EVC"></xref> is temporal scalabi
	lity. A media sender can remove NAL units belonging to higher temporal sub-layer
	s (i.e., those NAL units with a large value of TID) until the sending bitrate dr
	ops to an acceptable range.</t>


	<t>The mechanisms mentioned above generally work within a defined profile and le	<t>Parameters used for declaring receiver capabilities are, in gener
	vel; therefore no renegotiation of the channel is required. Only when non-downgr	al, downgradable, i.e., they express the upper limit for a sender's possible beh
	adable parameters (such as profile) are required to be changed does it become ne	avior. Thus, a sender <bcp14>MAY</bcp14> select to set its encoder using only lo
	cessary to terminate and restart the RTP stream(s). This may be accomplished by	wer/lesser or equal values of these parameters.</t>
	using different RTP payload types.</t>	<t>When a sender's capabilities are declared with the configuration
		parameters, these parameters express a configuration that is acceptable for the
		sender to receive bitstreams. In order to achieve high interoperability levels,
		it is often advisable to offer multiple alternative configurations. It is imposs
		ible to offer multiple configurations in a single payload type. Thus, when multi
		ple configuration offers are made, each offer requires its own RTP payload type
		associated with the offer.</t>
		<t>An implementation <bcp14>SHOULD</bcp14> be able to understand all
		media type parameters (including all optional media type parameters), even if i
		t doesn't support the functionality related to the parameter. This, in conjuncti
		on with proper application logic in the implementation, allows the implementatio
		n, after having received an offer, to create an answer by potentially downgradin
		g one or more of the optional parameters to the point where the implementation c
		an cope. This leads to higher chances of interoperability beyond the most basic
		interop points (for which, as described above, no optional parameters are necess
		ary).</t>
		<aside><t>Informative note: In implementations of various H.26x vide
		o coding payload formats including those for <xref target="AVC"/> and <xref targ
		et="HEVC"/>, it was occasionally observed that implementations were incapable of
		parsing most (or all) of the optional parameters and hence rejected offers othe
		r than the most basic offers. As a result, the Offer/Answer exchange resulted in
		a baseline performance (using the default values for the optional parameters) w
		ith the resulting suboptimal user experience. However, there are valid reasons t
		o forego the implementation complexity of implementing the parsing of some or al
		l of the optional parameters, for example, when there is predetermined knowledge
		, not negotiated by an SDP-based Offer/Answer process, of the capabilities of th
		e involved systems (walled gardens, baseline requirements defined in application
		standards higher up in the stack, and similar).</t></aside>
		<t>An Answerer <bcp14>MAY</bcp14> extend the offer with additional m
		edia format configurations. However, to enable their usage, in most cases, a sec
		ond offer is required from the Offerer to provide the bitstream property paramet
		ers that the media sender will use. This also has the effect that the Offerer ha
		s to be able to receive this media format configuration, and not only to send it
		.</t>
		</section>
		</section>
		<section anchor="multicast">
		<name>Multicast</name>
		<t>For bitstreams being delivered over multicast, the following rules
		apply:</t>
		<ul spacing="normal">
		<li><t>The media format configuration is identified by profile-id
		and level-id. These media format configuration parameters,
		including level-id, <bcp14>MUST</bcp14> be used symmetrically;
		that is, the Answerer <bcp14>MUST</bcp14> either maintain all
		configuration parameters or remove the media format (payload type)
		completely. Note that this implies that the level-id for
		Offer/Answer in multicast is not changeable.</t></li>
		<li><t>To simplify the handling and matching of these
		configurations, the same RTP payload type number used in the offer
		<bcp14>SHOULD</bcp14> also be used in the answer, as specified in
		<xref target="RFC3264"/>. An answer <bcp14>MUST NOT</bcp14>
		contain a payload type number used in the offer unless the
		configuration is the same as in the offer.</t></li>
		<li><t>Parameter sets received <bcp14>MUST</bcp14> be associated
		with the originating source and <bcp14>MUST</bcp14> only be used
		in decoding the incoming bitstream from the same source.</t></li>
		<li><t>The rules for other parameters are the same as above for
		unicast as long as the three above rules are obeyed.</t></li>
		</ul>
		</section>
		<section anchor="declativeSessiondesc">
		<name>Usage in Declarative Session Descriptions</name>
		<t>When EVC over RTP is offered with SDP in a declarative style, as in
		the Real-Time Streaming Protocol (RTSP) <xref target="RFC7826"/> or Session Ann
		ouncement Protocol (SAP) <xref target="RFC2974"/>, the following considerations
		apply.</t>
		<ul spacing="normal">
		<li><t>All parameters capable of indicating both bitstream propertie
		s and receiver capabilities are used to indicate only bitstream properties. For
		example, in this case, the parameters profile-id and level-id declare the values
		used by the bitstream, not the capabilities for receiving bitstreams. As a resu
		lt, the following interpretation of the parameters <bcp14>MUST</bcp14> be used:<
		/t>


	<t>MANEs MAY remove certain unusable packets from the RTP stream when that RTP s	<ul><li>
	tream was damaged due to previous packet losses. This can help reduce the networ	<t>Declaring actual configuration or bitstream properties:</t>
	k load in certain special cases. For example, MANEs can remove those FUs where t	<ul spacing="compact"><li><t>profile-id</t></li>
	he leading FUs belonging to the same NAL unit have been lost, because the traili	<li><t>level-id</t></li>
	ng FUs are meaningless to most decoders. MANE can also remove higher temporal sc	<li><t>sprop-sps</t></li>
	alable layers if the outbound transmission (from the MANE's viewpoint) exper	<li><t>sprop-pps</t></li>
	iences congestion.</t>	<li><t>sprop-max-don-diff</t></li>
		<li><t>sprop-depack-buf-bytes</t></li>
		<li><t>sprop-sei</t></li></ul></li>
		<li>
		<t>Not usable (when present, they <bcp14>MUST</bcp14> be ignored):</t>
		<ul spacing="compact"><li>
		<t>depack-buf-cap</t></li>
		<li><t>recv-sublayer-id</t></li>
		</ul>
		</li>
		<li> <t>A receiver of the SDP is required to support all parameters and
		values of the parameters provided; otherwise, the receiver <bcp14>MUST</bcp14>
		reject (RTSP) or not participate in (SAP) the session. It falls on the creator o
		f the session to use values that are expected to be supported by the receiving a
		pplication.</t></li>
		</ul>
		</li>
		</ul>
		</section>
		<section anchor="consider4pps">
		<name>Considerations for Parameter Sets</name>
		<t>When out-of-band transport of parameter sets is used, parameter set
		s <bcp14>MAY</bcp14> still be additionally transported in-band unless explicitly
		disallowed by an application, and some of these additional parameter sets may u
		pdate some of the out-of-band transported parameter sets. An update of a paramet
		er set refers to the sending of a parameter set of the same type using the same
		parameter set ID but with different values for at least one other parameter of t
		he parameter set.</t>

	</section>	</section>

	<section anchor="iana-considerations"><name>IANA Considerations</name>	</section>
		</section>
	<t>A new media type, as specified in <xref target="oparams"/> of this document,	<section anchor="FeedbackMessage">
	has been registered with IANA.</t>	<name>Use with Feedback Messages</name>


	</section>	<t>The following subsections define the use of the Picture Loss Indication
	<section anchor="acknowledgements"><name>Acknowledgements</name>	(PLI) <xref target="RFC4585" format="default"/> and Full Intra Request (FIR) <x
		ref target="RFC5104" format="default"/> feedback messages with <xref target="EVC
		"/>.</t>
		<t>In accordance with this document, a sender <bcp14>MUST NOT</bcp14> send
		Slice Loss Indication (SLI) or Reference Picture Selection Indication (RPSI); a
		nd a receiver <bcp14>MUST</bcp14> ignore RPSI and <bcp14>MUST</bcp14> treat a re
		ceived SLI as a received PLI, ignoring the "First", "Number", and "PictureID" fi
		elds of the PLI.</t>


	<t>Large parts of this specification share text with the RTP payload format for	<section anchor="PLI">
	VVC <xref target="RFC9328"/>. Roman Chernyak is thanksed for his valueable revie	<name>Picture Loss Indication (PLI)</name>
	w comments. We thank the authors of that specification for their excellent work.	<t>As specified in <xref target="RFC4585" sectionFormat="of" section="6.
	</t>	3.1"/>, the reception of a PLI by a media sender indicates "the loss of an undef
		ined amount of coded video data belonging to one or more pictures". Without havi
		ng any specific knowledge of the setup of the bitstream (such as use and locatio
		n of in-band parameter sets, IDR picture locations, picture structures, and so f
		orth), a reaction to the reception of a PLI by an EVC sender <bcp14>SHOULD</bcp1
		4> be to send an IDR picture and relevant parameter sets, potentially with suffi
		cient redundancy so as to ensure correct reception. However, sometimes informati
		on about the bitstream structure is known. For example, such information can be
		parameter sets that have been conveyed out of band through mechanisms not define
		d in this document and that are known to stay static for the duration of the ses
		sion. In that case, it is obviously unnecessary to send them in-band as a result
		of the reception of a PLI. Other examples could be devised based on a priori kn
		owledge of different aspects of the bitstream structure. In all cases, the timin
		g and congestion-control mechanisms of <xref target="RFC4585"/> <bcp14>MUST</bcp
		14> be observed.</t>

	</section>	</section>

		<section anchor="FIR">
		<name>Full Intra Request (FIR)</name>
		<t>The purpose of the FIR message is to force an encoder to send an inde
		pendent decoder refresh point as soon as possible while observing applicable con
		gestion-control-related constraints, such as those set out in <xref target="RFC8
		082"/>.</t>
		<t>Upon reception of a FIR, a sender <bcp14>MUST</bcp14> send an IDR pic
		ture. Parameter sets <bcp14>MUST</bcp14> also be sent, except when there is a pr
		iori knowledge that the parameter sets have been correctly established. A typica
		l example for that is an understanding between the sender and receiver, establis
		hed by means outside this document, that parameter sets are exclusively sent out
		of band.</t>
		</section>
		</section>
		<section anchor="Security">
		<name>Security Considerations</name>
		<t>The scope of this section is limited to the payload format itself and t
		o one feature of <xref target="EVC"/> that may pose a particularly serious secur
		ity risk if implemented naively. The payload format, in isolation, does not form
		a complete system. Implementers are advised to read and understand relevant sec
		urity-related documents, especially those pertaining to RTP (see the Security Co
		nsiderations in <xref target="RFC3550" sectionFormat="of" section="14"/>) and th
		e security of the call-control stack chosen (that may make use of the media type
		registration of this document). Implementers should also consider known securit
		y vulnerabilities of video coding and decoding implementations in general and av
		oid those.</t>
		<t>Within this RTP payload format, and with the exception of the user data
		SEI message as described below, no security threats other than those common to
		RTP payload formats are known. In other words, neither the various media-plane-b
		ased mechanisms nor the signaling part of this document seem to pose a security
		risk beyond those common to all RTP-based systems.</t>
		<t>RTP packets using the payload format defined in this specification are
		subject to the security considerations discussed in the RTP specification <xref
		target="RFC3550"/> and in any applicable RTP profile such as RTP/AVP <xref targe
		t="RFC3551"/>, RTP/AVPF <xref target="RFC4585"/>, RTP/SAVP <xref target="RFC3711
		"/>, or RTP/SAVPF <xref target="RFC5124"/>. However, as "<xref target="RFC7202"
		format="title"/>" <xref target="RFC7202" format="default"/> discusses, it is no
		t an RTP payload format's responsibility to discuss or mandate what solutions ar
		e used to meet the basic security goals like confidentiality, integrity, and sou
		rce authenticity for RTP in general. This responsibility lies on anyone using R
		TP in an application. They can find guidance on available security mechanisms a
		nd important considerations in "<xref target="RFC7201" format="title"/>" <xref t
		arget="RFC7201" format="default"/>. Applications <bcp14>SHOULD</bcp14> use one o
		r more appropriate strong security mechanisms. The rest of this section discuss
		es the security impacting properties of the payload format itself.</t>
		<t>Because the data compression used with this payload format is applied e
		nd to end, any encryption needs to be performed after compression. A potential d
		enial-of-service threat exists for data encodings using compression techniques t
		hat have non-uniform receiver-end computational load. The attacker can inject p
		athological datagrams into the bitstream that are complex to decode and that cau
		se the receiver to be overloaded.</t>
		<t>EVC is particularly vulnerable to such attacks, as it is extremely simp
		le to generate datagrams containing NAL units that affect the decoding process o
		f many future NAL units. Therefore, the usage of data origin authentication and
		data integrity protection of at least the RTP packet is <bcp14>RECOMMENDED</bcp1
		4> based on <xref target="RFC7202"/>.</t>
		<t>Like HEVC <xref target="RFC7798"/> and VVC <xref target="VVC"/>, EVC <x
		ref target="EVC"/> includes a user data Supplemental Enhancement Information (SE
		I) message. This SEI message allows inclusion of an arbitrary bitstring into the
		video bitstream. Such a bitstring could include JavaScript, machine code, and o
		ther active content.</t>
		<t>EVC <xref target="EVC"/> leaves the handling of this SEI message to the
		receiving system. In order to avoid harmful side effects of the user data SEI m
		essage, decoder implementations cannot naively trust its content. For example, f
		orwarding all received JavaScript code detected by a decoder implementation to a
		web browser unchecked would be a bad and insecure implementation practice. The
		safest way to deal with user data SEI messages is to simply discard them, but th
		at can have negative side effects on the quality of experience by the user.</t>
		<t>End-to-end security with authentication, integrity, or confidentiality
		protection will prevent a MANE from performing media-aware operations other than
		discarding complete packets. In the case of confidentiality protection, it wil
		l even be prevented from discarding packets in a media-aware way. To be allowed
		to perform such operations, a MANE is required to be a trusted entity that is i
		ncluded in the security context establishment.</t>
		</section>
		<section anchor="CC">
		<name>Congestion Control</name>
		<t>Congestion control for RTP <bcp14>SHALL</bcp14> be used in accordance w
		ith RTP <xref target="RFC3550"/> and with any applicable RTP profile, e.g., AVP
		<xref target="RFC3551"/> or AVPF <xref target="RFC4585"/>. If best-effort servic
		e is being used, an additional requirement is that users of this payload format
		<bcp14>MUST</bcp14> monitor packet loss to ensure that the packet loss rate is w
		ithin an acceptable range. Packet loss is considered acceptable if a TCP flow ac
		ross the same network path and experiencing the same network conditions would ac
		hieve an average throughput, measured on a reasonable timescale, that is not les
		s than all RTP streams combined. This condition can be satisfied by implementing
		congestion-control mechanisms to adapt the transmission rate by implementing th
		e number of layers subscribed for a layered multicast session or by arranging fo
		r a receiver to leave the session if the loss rate is unacceptably high.</t>
		<t>The bitrate adaptation necessary for obeying the congestion control pri
		nciple is easily achievable when real-time encoding is used, for example, by ade
		quately tuning the quantization parameter. However, when pre-encoded content is
		being transmitted, bandwidth adaptation requires the pre-coded bitstream to be t
		ailored for such adaptivity.</t>
		<t>The key mechanism available in <xref target="EVC"/> is temporal scalabi
		lity. A media sender can remove NAL units belonging to higher temporal sub-layer
		s (i.e., those NAL units with a large value of TID) until the sending bitrate dr
		ops to an acceptable range.</t>
		<t>The mechanisms mentioned above generally work within a defined profile
		and level; therefore, no renegotiation of the channel is required. Only when non
		-downgradable parameters (such as the profile) are required to be changed does i
		t become necessary to terminate and restart the RTP streams. This may be accompl
		ished by using different RTP payload types.</t>
		<t>MANEs <bcp14>MAY</bcp14> remove certain unusable packets from the RTP s
		tream when that RTP stream was damaged due to previous packet losses. This can h
		elp reduce the network load in certain special cases. For example, MANEs can rem
		ove those FUs where the leading FUs belonging to the same NAL unit have been los
		t, because the trailing FUs are meaningless to most decoders. MANE can also remo
		ve higher temporal scalable layers if the outbound transmission (from the MANE's
		viewpoint) experiences congestion.</t>
		</section>
		<section anchor="iana-considerations">
		<name>IANA Considerations</name>
		<t>The media type specified in <xref target="oparams"/> has been registere
		d with IANA.</t>
		</section>

	</middle>	</middle>


	<back>	<back>

		<references>
		<name>References</name>
		<references>
		<name>Normative References</name>


	<references title='Normative References'>	<reference anchor="EVC" target="https://www.iso.org/standard/57797.html"
		>
	<reference anchor="ISO23094-1" target="https://www.iso.org/standard/57797.html">	<front>
	<front>	<title>Information technology -- General video coding -- Part 1: Ess
	<title>ISO/IEC DIS Information technology --- General video coding --- Part	ential video
	1 Essential video coding</title>	coding</title>
	<author >	<author>
	<organization></organization>	<organization/>
	</author>	</author>
	<date year="n.d."/>	<date month="October" year="2020"/>
	</front>	</front>
	</reference>	<seriesInfo name="ISO/IEC" value="23094-1:2020"/>
	<reference anchor="EVC" target="https://www.iso.org/standard/57797.html">	</reference>
	<front>
	<title>ISO/IEC 23094-1 Essential Video Coding</title>
	<author >
	<organization></organization>
	</author>
	<date year="2020"/>
	</front>
	</reference>

	<reference anchor="RFC9328">
	<front>
	<title>RTP Payload Format for Versatile Video Coding (VVC)</title>
	<author fullname="S. Zhao" initials="S." surname="Zhao"/>
	<author fullname="S. Wenger" initials="S." surname="Wenger"/>
	<author fullname="Y. Sanchez" initials="Y." surname="Sanchez"/>
	<author fullname="Y.-K. Wang" initials="Y.-K." surname="Wang"/>
	<author fullname="M. M Hannuksela" initials="M. M" surname="Hannuksela"/>
	<date month="December" year="2022"/>
	<abstract>
	<t>This memo describes an RTP payload format for the Versatile Video Codin
	g (VVC) specification, which was published as both ITU-T Recommendation H.266 an
	d ISO/IEC International Standard 23090-3. VVC was developed by the Joint Video E
	xperts Team (JVET). The RTP payload format allows for packetization of one or mo
	re Network Abstraction Layer (NAL) units in each RTP packet payload, as well as
	fragmentation of a NAL unit into multiple RTP packets. The payload format has wi
	de applicability in videoconferencing, Internet video streaming, and high-bitrat
	e entertainment-quality video, among other applications.</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="9328"/>
	<seriesInfo name="DOI" value="10.17487/RFC9328"/>
	</reference>

	<reference anchor="RFC2119">
	<front>
	<title>Key words for use in RFCs to Indicate Requirement Levels</title>
	<author fullname="S. Bradner" initials="S." surname="Bradner"/>
	<date month="March" year="1997"/>
	<abstract>
	<t>In many standards track documents several words are used to signify the
	requirements in the specification. These words are often capitalized. This docu
	ment defines these words as they should be interpreted in IETF documents. This d
	ocument specifies an Internet Best Current Practices for the Internet Community,
	and requests discussion and suggestions for improvements.</t>
	</abstract>
	</front>
	<seriesInfo name="BCP" value="14"/>
	<seriesInfo name="RFC" value="2119"/>
	<seriesInfo name="DOI" value="10.17487/RFC2119"/>
	</reference>

	<reference anchor="RFC3550">
	<front>
	<title>RTP: A Transport Protocol for Real-Time Applications</title>
	<author fullname="H. Schulzrinne" initials="H." surname="Schulzrinne"/>
	<author fullname="S. Casner" initials="S." surname="Casner"/>
	<author fullname="R. Frederick" initials="R." surname="Frederick"/>
	<author fullname="V. Jacobson" initials="V." surname="Jacobson"/>
	<date month="July" year="2003"/>
	<abstract>
	<t>This memorandum describes RTP, the real-time transport protocol. RTP pr
	ovides end-to-end network transport functions suitable for applications transmit
	ting real-time data, such as audio, video or simulation data, over multicast or
	unicast network services. RTP does not address resource reservation and does not
	guarantee quality-of- service for real-time services. The data transport is aug
	mented by a control protocol (RTCP) to allow monitoring of the data delivery in
	a manner scalable to large multicast networks, and to provide minimal control an
	d identification functionality. RTP and RTCP are designed to be independent of t
	he underlying transport and network layers. The protocol supports the use of RTP
	-level translators and mixers. Most of the text in this memorandum is identical
	to RFC 1889 which it obsoletes. There are no changes in the packet formats on th
	e wire, only changes to the rules and algorithms governing how the protocol is u
	sed. The biggest change is an enhancement to the scalable timer algorithm for ca
	lculating when to send RTCP packets in order to minimize transmission in excess
	of the intended rate when many participants join a session simultaneously. [STAN
	DARDS-TRACK]</t>
	</abstract>
	</front>
	<seriesInfo name="STD" value="64"/>
	<seriesInfo name="RFC" value="3550"/>
	<seriesInfo name="DOI" value="10.17487/RFC3550"/>
	</reference>

	<reference anchor="RFC3551">
	<front>
	<title>RTP Profile for Audio and Video Conferences with Minimal Control</tit
	le>
	<author fullname="H. Schulzrinne" initials="H." surname="Schulzrinne"/>
	<author fullname="S. Casner" initials="S." surname="Casner"/>
	<date month="July" year="2003"/>
	<abstract>
	<t>This document describes a profile called "RTP/AVP" for the use of the r
	eal-time transport protocol (RTP), version 2, and the associated control protoco
	l, RTCP, within audio and video multiparticipant conferences with minimal contro
	l. It provides interpretations of generic fields within the RTP specification su
	itable for audio and video conferences. In particular, this document defines a s
	et of default mappings from payload type numbers to encodings. This document als
	o describes how audio and video data may be carried within RTP. It defines a set
	of standard encodings and their names when used within RTP. The descriptions pr
	ovide pointers to reference implementations and the detailed standards. This doc
	ument is meant as an aid for implementors of audio, video and other real-time mu
	ltimedia applications. This memorandum obsoletes RFC 1890. It is mostly backward
	s-compatible except for functions removed because two interoperable implementati
	ons were not found. The additions to RFC 1890 codify existing practice in the us
	e of payload formats under this profile and include new payload formats defined
	since RFC 1890 was published. [STANDARDS-TRACK]</t>
	</abstract>
	</front>
	<seriesInfo name="STD" value="65"/>
	<seriesInfo name="RFC" value="3551"/>
	<seriesInfo name="DOI" value="10.17487/RFC3551"/>
	</reference>

	<reference anchor="RFC3711">
	<front>
	<title>The Secure Real-time Transport Protocol (SRTP)</title>
	<author fullname="M. Baugher" initials="M." surname="Baugher"/>
	<author fullname="D. McGrew" initials="D." surname="McGrew"/>
	<author fullname="M. Naslund" initials="M." surname="Naslund"/>
	<author fullname="E. Carrara" initials="E." surname="Carrara"/>
	<author fullname="K. Norrman" initials="K." surname="Norrman"/>
	<date month="March" year="2004"/>
	<abstract>
	<t>This document describes the Secure Real-time Transport Protocol (SRTP),
	a profile of the Real-time Transport Protocol (RTP), which can provide confiden
	tiality, message authentication, and replay protection to the RTP traffic and to
	the control traffic for RTP, the Real-time Transport Control Protocol (RTCP). [
	STANDARDS-TRACK]</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="3711"/>
	<seriesInfo name="DOI" value="10.17487/RFC3711"/>
	</reference>

	<reference anchor="RFC4585">
	<front>
	<title>Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-
	Based Feedback (RTP/AVPF)</title>
	<author fullname="J. Ott" initials="J." surname="Ott"/>
	<author fullname="S. Wenger" initials="S." surname="Wenger"/>
	<author fullname="N. Sato" initials="N." surname="Sato"/>
	<author fullname="C. Burmeister" initials="C." surname="Burmeister"/>
	<author fullname="J. Rey" initials="J." surname="Rey"/>
	<date month="July" year="2006"/>
	<abstract>
	<t>Real-time media streams that use RTP are, to some degree, resilient aga
	inst packet losses. Receivers may use the base mechanisms of the Real-time Trans
	port Control Protocol (RTCP) to report packet reception statistics and thus allo
	w a sender to adapt its transmission behavior in the mid-term. This is the sole
	means for feedback and feedback-based error repair (besides a few codec-specific
	mechanisms). This document defines an extension to the Audio-visual Profile (AV
	P) that enables receivers to provide, statistically, more immediate feedback to
	the senders and thus allows for short-term adaptation and efficient feedback-bas
	ed repair mechanisms to be implemented. This early feedback profile (AVPF) maint
	ains the AVP bandwidth constraints for RTCP and preserves scalability to large g
	roups. [STANDARDS-TRACK]</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="4585"/>
	<seriesInfo name="DOI" value="10.17487/RFC4585"/>
	</reference>

	<reference anchor="RFC5124">
	<front>
	<title>Extended Secure RTP Profile for Real-time Transport Control Protocol
	(RTCP)-Based Feedback (RTP/SAVPF)</title>
	<author fullname="J. Ott" initials="J." surname="Ott"/>
	<author fullname="E. Carrara" initials="E." surname="Carrara"/>
	<date month="February" year="2008"/>
	<abstract>
	<t>An RTP profile (SAVP) for secure real-time communications and another p
	rofile (AVPF) to provide timely feedback from the receivers to a sender are defi
	ned in RFC 3711 and RFC 4585, respectively. This memo specifies the combination
	of both profiles to enable secure RTP communications with feedback. [STANDARDS-T
	RACK]</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="5124"/>
	<seriesInfo name="DOI" value="10.17487/RFC5124"/>
	</reference>


	<reference anchor="RFC8174">	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
	<front>	328.xml"/>
	<title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title>	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2
	<author fullname="B. Leiba" initials="B." surname="Leiba"/>	119.xml"/>
	<date month="May" year="2017"/>	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3
	<abstract>	550.xml"/>
	<t>RFC 2119 specifies common key words that may be used in protocol specif	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3
	ications. This document aims to reduce the ambiguity by clarifying that only UPP	551.xml"/>
	ERCASE usage of the key words have the defined special meanings.</t>	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3
	</abstract>	711.xml"/>
	</front>	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
	<seriesInfo name="BCP" value="14"/>	585.xml"/>
	<seriesInfo name="RFC" value="8174"/>	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
	<seriesInfo name="DOI" value="10.17487/RFC8174"/>	124.xml"/>
	</reference>	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
		174.xml"/>
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3
		264.xml"/>
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
		866.xml"/>
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
		648.xml"/>
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
		576.xml"/>
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5
		104.xml"/>
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
		082.xml"/>
		<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
		826.xml"/>


	<reference anchor="RFC3264">	<reference anchor="VSEI" target="https://www.itu.int/rec/T-REC-H.274">
	<front>	<front>
	<title>An Offer/Answer Model with Session Description Protocol (SDP)</title>	<title>Versatile supplemental enhancement information messages for c
	<author fullname="J. Rosenberg" initials="J." surname="Rosenberg"/>	oded video bitstreams</title>
	<author fullname="H. Schulzrinne" initials="H." surname="Schulzrinne"/>	<author>
	<date month="June" year="2002"/>	<organization>ITU-T</organization>
	<abstract>	</author>
	<t>This document defines a mechanism by which two entities can make use of	<date month="March" year="2024"/>
	the Session Description Protocol (SDP) to arrive at a common view of a multimed	</front>
	ia session between them. In the model, one participant offers the other a descri	<seriesInfo name="ITU-T Recommendation" value="H.274"/>
	ption of the desired session from their perspective, and the other participant a	</reference>
	nswers with the desired session from their perspective. This offer/answer model
	is most useful in unicast sessions where information from both participants is n
	eeded for the complete view of the session. The offer/answer model is used by pr
	otocols like the Session Initiation Protocol (SIP). [STANDARDS-TRACK]</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="3264"/>
	<seriesInfo name="DOI" value="10.17487/RFC3264"/>
	</reference>


	<reference anchor="RFC8866">	</references>
	<front>	<references>
	<title>SDP: Session Description Protocol</title>	<name>Informative References</name>
	<author fullname="A. Begen" initials="A." surname="Begen"/>
	<author fullname="P. Kyzivat" initials="P." surname="Kyzivat"/>
	<author fullname="C. Perkins" initials="C." surname="Perkins"/>
	<author fullname="M. Handley" initials="M." surname="Handley"/>
	<date month="January" year="2021"/>
	<abstract>
	<t>This memo defines the Session Description Protocol (SDP). SDP is intend
	ed for describing multimedia sessions for the purposes of session announcement,
	session invitation, and other forms of multimedia session initiation. This docum
	ent obsoletes RFC 4566.</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="8866"/>
	<seriesInfo name="DOI" value="10.17487/RFC8866"/>
	</reference>


	<reference anchor="RFC4648">	<reference anchor="MPEG2S">
	<front>	<front>
	<title>The Base16, Base32, and Base64 Data Encodings</title>	<title>Information technology - Generic coding of moving pictures an
	<author fullname="S. Josefsson" initials="S." surname="Josefsson"/>	d associated audio information - Part 1: Systems</title>
	<date month="October" year="2006"/>	<author>
	<abstract>	<organization>IS0/IEC</organization>
	<t>This document describes the commonly used base 64, base 32, and base 16	</author>
	encoding schemes. It also discusses the use of line-feeds in encoded data, use	<date month="June" year="2013"/>
	of padding in encoded data, use of non-alphabet characters in encoded data, use	</front>
	of different encoding alphabets, and canonical encodings. [STANDARDS-TRACK]</t>	<seriesInfo name="ISO/IEC" value="13818-1:2013"/>
	</abstract>	</reference>
	</front>
	<seriesInfo name="RFC" value="4648"/>
	<seriesInfo name="DOI" value="10.17487/RFC4648"/>
	</reference>


	<reference anchor="RFC5576">	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
	<front>	184.xml"/>
	<title>Source-Specific Media Attributes in the Session Description Protocol	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6
	(SDP)</title>	190.xml"/>
	<author fullname="J. Lennox" initials="J." surname="Lennox"/>	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
	<author fullname="J. Ott" initials="J." surname="Ott"/>	656.xml"/>
	<author fullname="T. Schierl" initials="T." surname="Schierl"/>	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
	<date month="June" year="2009"/>	667.xml"/>
	<abstract>	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
	<t>The Session Description Protocol (SDP) provides mechanisms to describe	201.xml"/>
	attributes of multimedia sessions and of individual media streams (e.g., Real-ti	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
	me Transport Protocol (RTP) sessions) within a multimedia session, but does not	202.xml"/>
	provide any mechanism to describe individual media sources within a media stream	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7
	. This document defines a mechanism to describe RTP media sources, which are ide	798.xml"/>
	ntified by their synchronization source (SSRC) identifiers, in SDP, to associate	<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2
	attributes with these sources, and to express relationships among sources. It a	974.xml"/>
	lso defines several source-level attributes that can be used to describe propert
	ies of media sources. [STANDARDS-TRACK]</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="5576"/>
	<seriesInfo name="DOI" value="10.17487/RFC5576"/>
	</reference>


	<reference anchor="RFC5104">	<reference anchor="HEVC" target="https://www.itu.int/rec/T-REC-H.265">
	<front>	<front>
	<title>Codec Control Messages in the RTP Audio-Visual Profile with Feedback	<title>High efficiency video coding</title>
	(AVPF)</title>	<author>
	<author fullname="S. Wenger" initials="S." surname="Wenger"/>	<organization>ITU-T</organization>
	<author fullname="U. Chandra" initials="U." surname="Chandra"/>	</author>
	<author fullname="M. Westerlund" initials="M." surname="Westerlund"/>	<date month="November" year="2019"/>
	<author fullname="B. Burman" initials="B." surname="Burman"/>	</front>
	<date month="February" year="2008"/>	<seriesInfo name="ITU-T Recommendation" value="H.265"/>
	<abstract>	</reference>
	<t>This document specifies a few extensions to the messages defined in the
	Audio-Visual Profile with Feedback (AVPF). They are helpful primarily in conver
	sational multimedia scenarios where centralized multipoint functionalities are i
	n use. However, some are also usable in smaller multicast environments and point
	-to-point calls.</t>
	<t>The extensions discussed are messages related to the ITU-T Rec. H.271 V
	ideo Back Channel, Full Intra Request, Temporary Maximum Media Stream Bit Rate,
	and Temporal-Spatial Trade-off. [STANDARDS-TRACK]</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="5104"/>
	<seriesInfo name="DOI" value="10.17487/RFC5104"/>
	</reference>


	<reference anchor="RFC8082">	<reference anchor="VIDEO-CODING" target="https://www.itu.int/rec/T-REC-H.
	<front>	263">
	<title>Using Codec Control Messages in the RTP Audio-Visual Profile with Fee	<front>
	dback with Layered Codecs</title>	<title>Video coding for low bit rate communication</title>
	<author fullname="S. Wenger" initials="S." surname="Wenger"/>	<author>
	<author fullname="J. Lennox" initials="J." surname="Lennox"/>	<organization>ITU-T</organization>
	<author fullname="B. Burman" initials="B." surname="Burman"/>	</author>
	<author fullname="M. Westerlund" initials="M." surname="Westerlund"/>	<date month="January" year="2005"/>
	<date month="March" year="2017"/>	</front>
	<abstract>	<seriesInfo name="ITU-T Recommendation" value="H.263"/>
	<t>This document updates RFC 5104 by fixing a shortcoming in the specifica	</reference>
	tion language of the Codec Control Message Full Intra Request (FIR) description
	when using it with layered codecs. In particular, a decoder refresh point needs
	to be sent by a media sender when a FIR is received on any layer of the layered
	bitstream, regardless of whether those layers are being sent in a single or in m
	ultiple RTP flows. The other payload-specific feedback messages defined in RFC 5
	104 and RFC 4585 (which was updated by RFC 5506) have also been analyzed, and no
	corresponding shortcomings have been found.</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="8082"/>
	<seriesInfo name="DOI" value="10.17487/RFC8082"/>
	</reference>


	<reference anchor="RFC7826">	<reference anchor="AVC" target="https://www.iso.org/standard/66069.html"
	<front>	>
	<title>Real-Time Streaming Protocol Version 2.0</title>	<front>
	<author fullname="H. Schulzrinne" initials="H." surname="Schulzrinne"/>	<title>Part 10: Advanced video coding</title>
	<author fullname="A. Rao" initials="A." surname="Rao"/>	<author>
	<author fullname="R. Lanphier" initials="R." surname="Lanphier"/>	<organization>ITU-T</organization>
	<author fullname="M. Westerlund" initials="M." surname="Westerlund"/>	</author>
	<author fullname="M. Stiemerling" initials="M." role="editor" surname="Stiem	<date month="October" year="2014"/>
	erling"/>	</front>
	<date month="December" year="2016"/>	<seriesInfo name="ITU-T Recommendation" value="H.264"/>
	<abstract>	</reference>
	<t>This memorandum defines the Real-Time Streaming Protocol (RTSP) version
	2.0, which obsoletes RTSP version 1.0 defined in RFC 2326.</t>
	<t>RTSP is an application-layer protocol for the setup and control of the
	delivery of data with real-time properties. RTSP provides an extensible framewor
	k to enable controlled, on-demand delivery of real-time data, such as audio and
	video. Sources of data can include both live data feeds and stored clips. This p
	rotocol is intended to control multiple data delivery sessions; provide a means
	for choosing delivery channels such as UDP, multicast UDP, and TCP; and provide
	a means for choosing delivery mechanisms based upon RTP (RFC 3550).</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="7826"/>
	<seriesInfo name="DOI" value="10.17487/RFC7826"/>
	</reference>


	<reference anchor="VSEI" target="https://www.itu.int/rec/T-REC-H.274">	<reference anchor="VVC" target="http://www.itu.int/rec/T-REC-H.266">
	<front>	<front>
	<title>Versatile supplemental enhancement information messages for coded vid	<title>Versatile video coding</title>
	eo bitstreams</title>	<author>
	<author >	<organization>ITU-T</organization>
	<organization></organization>	</author>
	</author>	<date month="August" year="2020"/>
	<date year="2020"/>	</front>
	</front>	<seriesInfo name="ITU-T Recommendation" value="H.266"/>
	</reference>	</reference>


		</references>
	</references>	</references>


	<references title='Informative References'>	<section anchor="acknowledgements" numbered="false" toc="default">
		<name>Acknowledgements</name>
	<reference anchor="MPEG2S" >	<t>Large parts of this specification share text with the RTP payload
	<front>	format for VVC <xref target="RFC9328"/>. <contact fullname="Roman
	<title>Information technology - Generic coding ofmoving pictures and associa	Chernyak"/> is thanked for his valuable review comments. We thank the
	ted audio information - Part 1:Systems, ISO International Standard 13818-1</titl	authors of that specification for their excellent work.</t>
	e>	</section>
	<author initials="" surname="IS0/IEC" fullname="IS0/IEC">
	<organization></organization>
	</author>
	<date year="2013"/>
	</front>
	</reference>

	<reference anchor="RFC6184">
	<front>
	<title>RTP Payload Format for H.264 Video</title>
	<author fullname="Y.-K. Wang" initials="Y.-K." surname="Wang"/>
	<author fullname="R. Even" initials="R." surname="Even"/>
	<author fullname="T. Kristensen" initials="T." surname="Kristensen"/>
	<author fullname="R. Jesup" initials="R." surname="Jesup"/>
	<date month="May" year="2011"/>
	<abstract>
	<t>This memo describes an RTP Payload format for the ITU-T Recommendation
	H.264 video codec and the technically identical ISO/IEC International Standard 1
	4496-10 video codec, excluding the Scalable Video Coding (SVC) extension and the
	Multiview Video Coding extension, for which the RTP payload formats are defined
	elsewhere. The RTP payload format allows for packetization of one or more Netwo
	rk Abstraction Layer Units (NALUs), produced by an H.264 video encoder, in each
	RTP payload. The payload format has wide applicability, as it supports applicati
	ons from simple low bitrate conversational usage, to Internet video streaming wi
	th interleaved transmission, to high bitrate video-on-demand.</t>
	<t>This memo obsoletes RFC 3984. Changes from RFC 3984 are summarized in S
	ection 14. Issues on backward compatibility to RFC 3984 are discussed in Section
	15. [STANDARDS-TRACK]</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="6184"/>
	<seriesInfo name="DOI" value="10.17487/RFC6184"/>
	</reference>

	<reference anchor="RFC6190">
	<front>
	<title>RTP Payload Format for Scalable Video Coding</title>
	<author fullname="S. Wenger" initials="S." surname="Wenger"/>
	<author fullname="Y.-K. Wang" initials="Y.-K." surname="Wang"/>
	<author fullname="T. Schierl" initials="T." surname="Schierl"/>
	<author fullname="A. Eleftheriadis" initials="A." surname="Eleftheriadis"/>
	<date month="May" year="2011"/>
	<abstract>
	<t>This memo describes an RTP payload format for Scalable Video Coding (SV
	C) as defined in Annex G of ITU-T Recommendation H.264, which is technically ide
	ntical to Amendment 3 of ISO/IEC International Standard 14496-10. The RTP payloa
	d format allows for packetization of one or more Network Abstraction Layer (NAL)
	units in each RTP packet payload, as well as fragmentation of a NAL unit in mul
	tiple RTP packets. Furthermore, it supports transmission of an SVC stream over a
	single as well as multiple RTP sessions. The payload format defines a new media
	subtype name "H264-SVC", but is still backward compatible to RFC 6184 since the
	base layer, when encapsulated in its own RTP stream, must use the H.264 media s
	ubtype name ("H264") and the packetization method specified in RFC 6184. The pay
	load format has wide applicability in videoconferencing, Internet video streamin
	g, and high-bitrate entertainment-quality video, among others. [STANDARDS-TRACK]
	</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="6190"/>
	<seriesInfo name="DOI" value="10.17487/RFC6190"/>
	</reference>

	<reference anchor="RFC7656">
	<front>
	<title>A Taxonomy of Semantics and Mechanisms for Real-Time Transport Protoc
	ol (RTP) Sources</title>
	<author fullname="J. Lennox" initials="J." surname="Lennox"/>
	<author fullname="K. Gross" initials="K." surname="Gross"/>
	<author fullname="S. Nandakumar" initials="S." surname="Nandakumar"/>
	<author fullname="G. Salgueiro" initials="G." surname="Salgueiro"/>
	<author fullname="B. Burman" initials="B." role="editor" surname="Burman"/>
	<date month="November" year="2015"/>
	<abstract>
	<t>The terminology about, and associations among, Real-time Transport Prot
	ocol (RTP) sources can be complex and somewhat opaque. This document describes a
	number of existing and proposed properties and relationships among RTP sources
	and defines common terminology for discussing protocol entities and their relati
	onships.</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="7656"/>
	<seriesInfo name="DOI" value="10.17487/RFC7656"/>
	</reference>

	<reference anchor="RFC7667">
	<front>
	<title>RTP Topologies</title>
	<author fullname="M. Westerlund" initials="M." surname="Westerlund"/>
	<author fullname="S. Wenger" initials="S." surname="Wenger"/>
	<date month="November" year="2015"/>
	<abstract>
	<t>This document discusses point-to-point and multi-endpoint topologies us
	ed in environments based on the Real-time Transport Protocol (RTP). In particula
	r, centralized topologies commonly employed in the video conferencing industry a
	re mapped to the RTP terminology.</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="7667"/>
	<seriesInfo name="DOI" value="10.17487/RFC7667"/>
	</reference>

	<reference anchor="RFC7201">
	<front>
	<title>Options for Securing RTP Sessions</title>
	<author fullname="M. Westerlund" initials="M." surname="Westerlund"/>
	<author fullname="C. Perkins" initials="C." surname="Perkins"/>
	<date month="April" year="2014"/>
	<abstract>
	<t>The Real-time Transport Protocol (RTP) is used in a large number of dif
	ferent application domains and environments. This heterogeneity implies that dif
	ferent security mechanisms are needed to provide services such as confidentialit
	y, integrity, and source authentication of RTP and RTP Control Protocol (RTCP) p
	ackets suitable for the various environments. The range of solutions makes it di
	fficult for RTP-based application developers to pick the most suitable mechanism
	. This document provides an overview of a number of security solutions for RTP a
	nd gives guidance for developers on how to choose the appropriate security mecha
	nism.</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="7201"/>
	<seriesInfo name="DOI" value="10.17487/RFC7201"/>
	</reference>

	<reference anchor="RFC7202">
	<front>
	<title>Securing the RTP Framework: Why RTP Does Not Mandate a Single Media S
	ecurity Solution</title>
	<author fullname="C. Perkins" initials="C." surname="Perkins"/>
	<author fullname="M. Westerlund" initials="M." surname="Westerlund"/>
	<date month="April" year="2014"/>
	<abstract>
	<t>This memo discusses the problem of securing real-time multimedia sessio
	ns. It also explains why the Real-time Transport Protocol (RTP) and the associat
	ed RTP Control Protocol (RTCP) do not mandate a single media security mechanism.
	This is relevant for designers and reviewers of future RTP extensions to ensure
	that appropriate security mechanisms are mandated and that any such mechanisms
	are specified in a manner that conforms with the RTP architecture.</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="7202"/>
	<seriesInfo name="DOI" value="10.17487/RFC7202"/>
	</reference>

	<reference anchor="RFC7798">
	<front>
	<title>RTP Payload Format for High Efficiency Video Coding (HEVC)</title>
	<author fullname="Y.-K. Wang" initials="Y.-K." surname="Wang"/>
	<author fullname="Y. Sanchez" initials="Y." surname="Sanchez"/>
	<author fullname="T. Schierl" initials="T." surname="Schierl"/>
	<author fullname="S. Wenger" initials="S." surname="Wenger"/>
	<author fullname="M. M. Hannuksela" initials="M. M." surname="Hannuksela"/>
	<date month="March" year="2016"/>
	<abstract>
	<t>This memo describes an RTP payload format for the video coding standard
	ITU-T Recommendation H.265 and ISO/IEC International Standard 23008-2, both als
	o known as High Efficiency Video Coding (HEVC) and developed by the Joint Collab
	orative Team on Video Coding (JCT-VC). The RTP payload format allows for packeti
	zation of one or more Network Abstraction Layer (NAL) units in each RTP packet p
	ayload as well as fragmentation of a NAL unit into multiple RTP packets. Further
	more, it supports transmission of an HEVC bitstream over a single stream as well
	as multiple RTP streams. When multiple RTP streams are used, a single transport
	or multiple transports may be utilized. The payload format has wide applicabili
	ty in videoconferencing, Internet video streaming, and high-bitrate entertainmen
	t-quality video, among others.</t>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="7798"/>
	<seriesInfo name="DOI" value="10.17487/RFC7798"/>
	</reference>

	<reference anchor="RFC2974">
	<front>
	<title>Session Announcement Protocol</title>
	<author fullname="M. Handley" initials="M." surname="Handley"/>
	<author fullname="C. Perkins" initials="C." surname="Perkins"/>
	<author fullname="E. Whelan" initials="E." surname="Whelan"/>
	<date month="October" year="2000"/>
	<abstract>
	<t>This document describes version 2 of the multicast session directory an
	nouncement protocol, Session Announcement Protocol (SAP), and the related issues
	affecting security and scalability that should be taken into account by impleme
	ntors. This memo defines an Experimental Protocol for the Internet community.</t
	>
	</abstract>
	</front>
	<seriesInfo name="RFC" value="2974"/>
	<seriesInfo name="DOI" value="10.17487/RFC2974"/>
	</reference>

	<reference anchor="HEVC" target="https://www.itu.int/rec/T-REC-H.265">
	<front>
	<title>High efficiency video coding, ITU-T Recommendation H.265</title>
	<author >
	<organization></organization>
	</author>
	<date year="2019"/>
	</front>
	</reference>
	<reference anchor="AVC" target="https://www.iso.org/standard/66069.html">
	<front>
	<title>ITU-T Recommendation H.264 - Advanced video coding for generic audiov
	isual services</title>
	<author >
	<organization></organization>
	</author>
	<date year="2014"/>
	</front>
	</reference>
	<reference anchor="VVC" target="http://www.itu.int/rec/T-REC-H.266">
	<front>
	<title>Versatile Video Coding, ITU-T Recommendation H.266</title>
	<author >
	<organization></organization>
	</author>
	<date year="2020"/>
	</front>
	</reference>

	</references>

	</back>	</back>


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