<?xmlversion="1.0" encoding="ascii"?> <?xml-stylesheet type="text/xsl" href="rfc2629.xslt" ?> <!-- generated by https://github.com/cabo/kramdown-rfc version 1.6.40 (Ruby 2.6.10) -->version='1.0' encoding='utf-8'?> <!DOCTYPE rfc [ <!ENTITY nbsp " "> <!ENTITY zwsp "​"> <!ENTITY nbhy "‑"> <!ENTITY wj "⁠"> ]> <rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft-ietf-avtcore-rtp-evc-07" number="9584" category="std" consensus="true" submissionType="IETF" obsoletes="" updates="" tocInclude="true" sortRefs="true"symRefs="true">symRefs="true" version="3" xml:lang="en"> <front> <title abbrev="RTPpayload formatPayload 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"> <organization>Intel</organization> <address> <postal> <street>2200 Mission College Blvd</street> <city>SantaClara</city>Clara</city><region>California</region> <code>95054</code><country>USA</country><country>United States of America</country> </postal> <email>shuai.zhao@ieee.org</email> </address> </author> <author initials="S." surname="Wenger" fullname="Stephan Wenger"> <organization>Tencent</organization> <address> <postal> <street>2747 Park Blvd</street> <city>PaloAlto</city>Alto</city><region>California</region> <code>94588</code><country>USA</country><country>United States of America</country> </postal> <email>stewe@stewe.org</email> </address> </author> <author initials="Y." surname="Lim" fullname="Youngkwon Lim"> <organization>Samsung Electronics</organization> <address> <postal> <street>6625 Excellence Way</street><city>Plano</city><city>Plano</city><region>Texas</region> <code>75013</code><country>USA</country><country>United States of America</country> </postal> <email>yklwhite@gmail.com</email> </address> </author> <dateyear="2023" month="December" day="19"/> <area>ART</area>year="2024" month="May"/> <area>WIT</area> <workgroup>avtcore</workgroup><keyword>Internet-Draft</keyword><keyword>EVC</keyword> <keyword>ISO/IEC 23094-1</keyword> <keyword>Essential Video Coding</keyword> <abstract><?line 113?><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 theMoving Picture Experts Group (MPEG).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> </front> <middle><?line 117?><sectionanchor="introduction"><name>Introduction</name>anchor="introduction"> <name>Introduction</name> <t>The Essential Video Coding <xref target="EVC"/> standard, which is formally designated as ISO/IEC International Standard 23094-1 <xreftarget="ISO23094-1"/> has beentarget="ISO23094-1"/>, was published in 2020. OnegoalofMPEGMPEG's goals is to keep<xref target="EVC"/>'sEVC's Baseline profile essentially royalty-free by using technologies published more than 20 years ago or otherwise known to be available for use without a requirement for paying royalties, whereas more advanced profiles follow a reasonable and non-discriminatory licensing terms policy. Both the Baseline profile and higher profiles of EVC <xref target="EVC"/> are reported to provide coding efficiency gains over High Efficiency Video Coding <xref target="HEVC"/> and Advanced Video Coding <xref target="AVC"/> under certain configurations.</t> <t>This document describes an RTP payload format for EVC. It shares its basic design with the NAL unit-based RTP payload formats of H.264 Video Coding <xref target="RFC6184"/>, Scalable Video Coding (SVC) <xref target="RFC6190"/>, High Efficiency Video Coding (HEVC) <xref target="RFC7798"/>, and Versatile Video Coding(VVC)<xref(VVC) <xref target="RFC9328"/>. With respect to design philosophy, security, congestion control, and overall implementation complexity, it has similar properties to those earlier payload format specifications. <!-- [rfced] Since it is the technology defined within the RFC, may we update to something like the following for clarity? Original: This is a conscious choice, as at least [RFC6184] is widely deployed and generally known in the relevant implementer communities. Perhaps: This is a conscious choice, as at least the RTP Payload Format as described in [RFC6184] is widely deployed and generally known in the relevant implementer communities. --> This is a conscious choice, as at least the RTP Payload Format for H.264 video as described in <xref target="RFC6184"/> is widely deployed and generally known in the relevant implementer communities. Certain mechanismsknown fromdescribed in <xref target="RFC6190"/> wereincorporatedincorporated, as EVC supports temporal scalability. EVC currently does not offer higher forms of scalability.</t> <sectionanchor="overview-of-the-evc-codec"><name>Overviewanchor="overview-of-the-evc-codec"> <name>Overview of the EVC Codec</name><t><xref<!-- [rfced] Similarly, may we update this text to indicate that the codings/technologies "share a similar hybrid video codec design"? Original: [EVC], [AVC], [HEVC] and [VVC] share a similar hybrid video codec design. Perhaps: The codings described in [EVC], [AVC], [HEVC], and [VVC] share a similar hybrid video codec design. --> <!-- [rfced] We do not see "general_constraint_flags" in [VVC] (http://www.itu.int/rec/T-REC-H.266). Does this perhaps refer to "general_constraints_info"? Please clarify. Original: EVC facilitates certain walled-garden implementations under commercial constraints imposed by intellectual property rights by including syntax elements that allow encoders to mark a bitstream as to what of the many independent coding tools are exercised in the bitstream, in a spirit similar to the general_constraint_flags of [VVC]. --> <!-- Note that we added a citation to [EVC] to clarify that it is the ISO/IEC standard that implementers are required to understand. Please let us know if any updates are required. Original: Implementers have to read, understand, and apply the ISO/IEC standard pertaining to EVC to arrive at interoperable, well-performing implementations. Current: Implementers have to read, understand, and apply the ISO/IEC standard pertaining to EVC [EVC] to arrive at interoperable, well-performing implementations. --> <t>The codings described in <xref target="EVC"/>, <xref target="AVC"/>, <xreftarget="HEVC"/>target="HEVC"/>, and <xref target="VVC"/> share a similar hybrid video codec 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. Implementers have to read, understand, and apply the ISO/IEC standard pertaining to EVC <xref target="EVC"/> to arrive at interoperable, well-performing implementations. The EVC standard has a Baseline profile and a Main profile, the latter being a superset of the Baseline profile but including more advanced features. EVC also includes still image variants of both Baseline and Main profiles, in each of which the bitstream is restricted to a single IDR picture. EVC facilitates certainwalled-gardenwalled garden implementations under commercial constraints imposed by intellectual property rights by including syntax elements that allow encoders to mark a bitstream as to what of the many independent coding tools are exercised in the bitstream, in a spirit similar to thegeneral_constraint_flagsgeneral_constraint_info of <xref target="VVC"/>.</t> <t>Conceptually, all EVC, AVC,HEVCHEVC, and VVC include a Video Coding Layer(VCL);(VCL), a term that is often used to refer to the coding-tool features, and a Network Abstraction Layer (NAL), which usually refers to the systems and transport interface aspects of the codecs.</t> <sectionanchor="coding-tool-features-informative"><name>Coding-Toolanchor="coding-tool-features-informative"> <name>Coding-Tool Features(informative)</name> <t>Coding(Informative)</name> <dl newline="true"> <dt>Coding blocks and transformstructure</t> <t>EVCstructure</dt> <dd><t>EVC uses a traditional block-based coding structure, which divides the encoded image into blocks of up to 64x64 luma samples for the Baseline profile and 128x128 luma samples for the Main profile that can be recursively divided into smaller blocks. <!-- [rfced] We are having trouble understanding "allows to divide". Please consider whether the suggested updated correctly conveys the intended meaning. Original: The baseline profiles utilize an HEVC-like quad-tree blocks partitioning that allows to divide a block horizontally and vertically onto four smaller square blocks. Perhaps: The Baseline profiles utilize HEVC-like quad-tree-blocks partitioning that allows a block to be divided horizontally and vertically into four smaller square blocks. --> The Baseline profiles utilize HEVC-like quad-tree-blocks partitioning that allows a block to be divided horizontally and vertically into four smaller square blocks. The Main profile adds two advanced coding structure tools: 1) Binary Ternary Tree (BTT) partitioning that allows non-square codingunits;units and 2) Split Unit Coding Order 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) predictions. A residue block is calculated by subtracting predicted data from the original (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 profile, Improved Quantization and Transform (IQT) uses a differentmapping/clippingmapping or clipping function for quantization. An inverse zig-zag scanning order is used for coefficient coding. Advanced Coefficient Coding (ADCC) in the Main profile can code coefficient values more efficiently, for example, indicated by the last non-zero coefficient. The Baseline profile uses a straightforwardrun-length encoding (RLE) basedRLE-based approach to encode the quantizedcoefficients.</t> <t>Entropy coding</t> <t>EVCcoefficients.</t></dd> <dt>Entropy coding</dt> <!-- [rfced] Would you like to define "binarization" in Section 3.1.1 (Definitions from the EVC Standard), as binarization is defined in [EVC] as: binarization set of bin strings (3.7) for all possible values of a syntax element (3.86) Original: The mechanism includes a binarization step and a probability update defined by a lookup table. --> <dd><t>EVC uses a similar binary arithmetic coding mechanism as HEVC CABAC (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><t>In-loop filtering</t> <t>The</dd> <dt>In-loop filtering</dt> <!-- [rfced] Please confirm that "H.263 Annex J." refers to the ITU-T Recommendation found at <https://www.itu.int/rec/T-REC-H.263>. If this is correct, will add an informative reference entry. Current: The Baseline profile of EVC uses the deblocking filter defined in H.263 Annex J. --> <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 profile, an Advanced Deblocking Filter (ADDB) can be used as an alternative, which can further reduce undesirable compression artifacts. The Main profile also defines two additional in-loop filters that can be used to improve the quality of decoded pictures before output and/or forinter-prediction.Inter prediction. A Hadamard Transform Domain Filter (HTDF) is applied to the luma samples before deblocking, and a lookup table is used to determine four adjacent samples for filtering. <!-- [rfced] We're having trouble understanding "allows to send". Please consider whether the suggested updated conveys the correct meaning. Original: An adaptive Loop Filter (ALF) allows to send signals of up to 25 different filters for the luma components, and the best filter can be selected through the classification process for each 4x4 block. Perhaps: An adaptive Loop Filter (ALF) allows signals of up to 25 different filters to be sent for the luma components; the best filter can be selected through the classification process for each 4x4 block. --> An adaptive Loop Filter (ALF) allows signals of up to 25 different filters to be sent for the luma components; the best filter can be selected through the classification process for each 4x4 block. Similarly to VVC, the filter parameters of ALF are signaled in the Adaptation Parameter Set(APS).</t> <t>Inter-prediction</t> <t>The(APS).</t></dd> <dt>Inter prediction</dt> <dd><t>The basis ofEVC's inter-predictionEVC's Inter prediction is motion compensation using interpolation filters with a quarter sample resolution. In the Baseline profile, a motion vector is transmitted using one of three spatially neighboring motion vectors and a temporally collocated motion vector as a predictor. A motion vector difference may be signaled relative to the selected predictor, but there is a case where no motion vector difference is signaled, and there is no remaining data in the block. This mode is called askip"skip" mode. The Main profile includes six additional tools to provide improvedinter-prediction.Inter prediction. With Advanced Motion Vectors Prediction (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 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 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 predictions for the block can be derived from its neighboring blocks in the same picture and collocated blocks in the reference picture. The Adaptive Motion Vector Resolution (AMVR) tool provides a way to reduce the accuracy of a motion vector from 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 Refinement (DMVR), which uses a bilateral template matching process to refine the motion vectors without additionalsignaling.</t> <t>Intrasignaling.</t></dd> <dt>Intra prediction andintra-coding</t> <t>Intraintra coding</dt> <dd><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 square, there are five different prediction modes: DC (mean value of the neighborhood), horizontal, vertical, and two different diagonal directions. In the Main profile, intra prediction can be applied to any rectangular coding unit, and 28 additional direction modes are available in theso-calledEnhanced Intra Prediction Directions(EIPD).(EIPDs). In the Main profile, an encoder can also use Intra Block Copy (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 indicate where the prediction block in the current picture is used for thismode.</t> <t>Referencemode.</t></dd> <dt>Reference framesmanagement</t> <t>Inmanagement</dt> <dd><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 profile, the management of the DPB (i.e., the process of adding and deleting reference pictures) is controlled by a straightforward AVC-like sliding window approach with very few parameters from theSPS.sequence parameter set (SPS). For the Main profile, DPB management can be handled much more flexibly using explicitly signaledreferenceReference Picture Lists(RPL)(RPLs) in the SPS or slicelevel.</t>level.</t></dd> </dl> </section> <sectionanchor="systems-and-transport-interfaces"><name>Systemsanchor="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 mechanism. The hierarchical syntax and data unit structure consists of a sequence-level parameter set(SPS),(i.e., SPS), two picture-level parameter sets(PPS(i.e., PPS and APS, each of which can apply to one or more pictures), slice-level header parameters, and lower-level parameters.</t> <t>A number of key components that influenced theNetwork Abstraction LayerNAL design of EVC as well as thisdocument,document are described below:</t><t>Sequence<dl newline="true"> <dt>Sequence parameterset</t> <ul empty="true"><li> <t>Theset</dt> <dd><t>The Sequence Parameter Set (SPS) contains syntax elements pertaining to a Coded Video Sequence (CVS), which is a group of pictures, starting 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 equivalent of a CVS is a Group of Pictures (GOP), which generallystartedstarts with an I frame and is followed by P and B frames. While more complex in its options of random 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 switchingMCUsMultipoint Control Units (MCUs) involved), a CVS can be as long in duration as the wholesession.</t> </li></ul> <t>Picturesession.</t></dd> <dt>Picture and adaptation parameterset</t> <ul empty="true"><li> <t>Theset</dt> <dd><t>The Picture Parameter Set (PPS) and the Adaptation Parameter Set(PPS and APS, respectively)(APS) carry information pertaining to a single picture. The PPS contains information that is likely to stay constant from picture to picture, at least for pictures of a certaintypetype; whereas the APS contains information, such as adaptive loop filter coefficients, that are likely to change from picture topicture.</t> </li></ul> <t>Profile,picture.</t></dd> <dt>Profile, level, andtoolsets</t> <ul empty="true"><li> <t>Profilestoolsets</dt> <dd><t>Profiles and levels follow the same design considerations known from AVC, HEVC, and video codecs as old as MPEG-1 Video. The profile defines a set of tools (not toconfusebe confused with the"toolset""toolset" discussed below) that a decoder compliant with this profile has to support. In EVC, profiles are defined in AnnexA.A of <xref target="EVC"/>. Formally, they are defined as a set of constraints that a bitstream needs to conform to. In EVC, the Baseline profile is much more severelyconstraintconstrained than the Main profile, reducing implementation complexity. Levels relate to bitstream complexity in dimensions such as maximum sample decoding rate, maximum picture size, and similar parameters directly related to computational complexity and/or memory demands.</t></li></ul><t>Profiles and levels are signaled in the highest parameter set available, the SPS.</t><ul empty="true"><li> <t>EVC<!-- [rfced] Should "syntax element" be plural when referring to toolset_idc_h and toolset_idc_l? We see "elements" (plural) later in the text. Please consider how/if the text should be updated. For example, should "the toolset syntax element" be "toolset syntax elements", and should "is a bitmask" be "are bitmasks"? Original (first sentence included because changes may be needed there as well): EVC contains another mechanism related to the use of coding tools, known as the toolset syntax element. This syntax element, toolset_idc_h and toolset_idc_l located in the SPS, is a bitmask that allows encoders to indicate which coding tools they are using within the menu of profiles offered by the profile that is also signaled. Original (refers to "syntax elements"): This parameter is a base64 encoding (Section 4 of [RFC4648]) representation of a 64 bit unsigned integer bit mask derived from the concatenation, in network byte order, of the syntax elements toolset_idc_h and toolset_idc_l. --> <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_idc_l (located in the SPS), are bitmasks that allow encoders to indicate which coding tools they are using within the menu of profiles offered by the profile that 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 used 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 garden implementations could do so without incurring the interoperability problems 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 property-related risks.</t></li></ul> <t>Bitstream</dd> <dt>Bitstream and elementarystream</t> <ul empty="true"><li> <t>Abovestream</dt> <dd><t>Above the Coded Video Sequence (CVS), EVC defines a video bitstream that can be used as an elementary stream in the MPEG systems context. For this document, the video bitstream syntax level is notrelevant.</t> </li></ul> <t>Randomrelevant.</t></dd> <dt>Random accesssupport</t> <ul empty="true"><li> <t>EVCsupport</dt> <dd><t>EVC supports random access mechanisms based on IDR andCRAclean random accessunits.</t> </li></ul> <t>Temporal(CRA) access units.</t></dd> <dt>Temporal scalabilitysupport</t> <ul empty="true"><li> <t>EVCsupport</dt> <dd><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_idfield.</t> </li></ul> <t>Referencefield.</t></dd> <dt>Reference picturemanagement</t> <ul empty="true"><li> <t>EVC'smanagement</dt> <!-- [rfced] For clarity and to avoid use of "available" twice in close proximity, may we update the first instance to "accessible", "offered", or otherwise? Original: In the Main profile, substantially all reference picture list manipulations available in HEVC are available, including explicit transmissions/updates of reference picture lists, although ... --> <dd><t>EVC's reference picture management isPOC-based (Picture Order Count),POC-based, similar to HEVC. In the Main profile, substantially all reference picture list manipulations available in HEVC areavailable,specified, including explicittransmissions/updatestransmissions or updates of reference picturelists, althoughlists. Although for reference pictures management purposes, EVC uses a modern VVC-like RPL approach, which is conceptually simpler than the HEVC one. In the Baseline profile, reference picture management is more restricted, allowing for a comparatively simple group of picture structuresonly.</t> </li></ul> <t>SEI Message</t> <ul empty="true"><li> <t>EVConly.</t></dd> <dt>SEI Message</dt> <dd><t>EVC inherits many ofHEVC'sHEVC's SEIMessages,messages, occasionally with syntax and/or semantics changes, making them applicable to EVC. In addition, some of the codec-agnostic SEIMessagesmessages of the VSEI specification <xref target="VSEI"/> are alsomapped.</t> </li></ul>mapped.</t></dd> </dl> </section> <sectionanchor="parallel-processing-support-informative"><name>Parallelanchor="parallel-processing-support-informative"> <name>Parallel Processing Support(informative)</name> <ul empty="true"><li> <t>EVC's(Informative)</name> <!-- [rfced] For clarity, may we update this sentence as follows? Original: The slices are defined as any rectangular region within a picture and can be encoded to have no coding dependencies with other slices in the same picture but with other slices from the previous picture. Perhaps: The slices are defined as 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. --> <t>EVC's Baseline profile includes no tools specifically addressingparallel processingparallel-processing support. The Main profile includes independently decodable slices for parallel processing. The slices are defined as any rectangular region within apicture andpicture. They can be encoded to havenocoding dependencies with other slicesinfrom thesameprevious picture but not with other slicesfromin theprevioussame picture. No specific support for parallel processing is specified in this RTP payload format.</t></li></ul></section> <sectionanchor="NALUnitHeader"><name>NALanchor="NALUnitHeader"> <name>NAL Unit Header</name> <t>EVC maintains the NAL unit concept of <xref target="VVC"/> with different 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 excluding the NAL unit header.</t> <figureanchor="evc-nuh"><artwork><![CDATA[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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |F| Type | TID | Reserve |E|+-------------+-----------------+ The Structure of the EVC NAL Unit Header ]]></artwork></figure>+-------------+-----------------+]]></artwork> </figure> <t>The semantics of the fields in the NAL unit header are as specified 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 provided.</t><t>F: 1<dl> <dt>F:</dt> <dd><t>1 bit</t><ul empty="true"><li> <t>forbidden_zero_bit. Required<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 <xreftarget="funits"/>.</t> </li></ul> <t>Type: 6target="funits"/>.</dd></dl> </dd> <dt>Type:</dt> <dd> <t>6 bits</t><ul empty="true"><li> <t>nal_unit_type_plus1. This<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></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 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 7.4.2.2inof <xref target="EVC"/>. Note that nal_unit_type_plus1MUST NOT<bcp14>MUST NOT</bcp14> bezero.</t> </li></ul> <t>TID: 3zero.</t></dd></dl> </dd> <dt>TID:</dt> <dd><t>3 bits</t><ul empty="true"><li> <t>nuh_temporal_id. This<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 type1).</t> </li></ul> <t>Reserve: 51).</dd></dl> </dd> <dt>Reserve:</dt> <dd><t>5 bits</t><ul empty="true"><li> <t>nuh_reserved_zero_5bits. This<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<xref target="EVC"/>'sAnnex 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 than0.</t> </li></ul> <t>E: 10.</dd></dl> </dd> <dt>E:</dt> <dd><t>1 bit</t><ul empty="true"><li> <t>nuh_extension_flag. This<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<xref target="EVC"/>'sAnnex 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 to1.</t> </li></ul>1.</dd></dl> </dd> </dl> </section> </section> <sectionanchor="overview-of-the-payload-format"><name>Overviewanchor="overview-of-the-payload-format"> <name>Overview of the Payload Format</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<ul spacing="normal"> <li>usage of RTP header with this payloadformat</t> <t>packetizationformat</li> <li>packetization of EVC-coded NAL units into RTP packets using three types of payload structures: a single NAL unit, aggregation, and fragmentunit</t> <t>transmissionunit</li> <li>transmission of EVC NAL units of the same bitstream within a single RTPstream.</t> <t>mediastream</li> <li>usage of media type parameters to be used with the Session Description Protocol (SDP) <xreftarget="RFC8866"/></t> <t>usagetarget="RFC8866"/></li> <li>usage of RTCP feedbackmessages</t> </list></t>messages</li> </ul> </section> </section> <sectionanchor="conventions"><name>Conventions</name> <t>Theanchor="conventions"> <name>Conventions</name> <t> The key words"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY","<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"OPTIONAL""<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as described inBCP 14BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when, they appear in all capitals, as shownabove.</t>here. </t> </section> <sectionanchor="definitionsandabbr"><name>Definitionsanchor="definitionsandabbr"> <name>Definitions and Abbreviations</name> <sectionanchor="definitions"><name>Definitions</name>anchor="definitions"> <name>Definitions</name> <t>This document uses the terms and definitions of EVC. <xref target="definitionforevc"/> lists relevant definitions from <xref target="EVC"/> for convenience. <xref target="def"/> provides definitions specific to this document.</t> <sectionanchor="definitionforevc"><name>Definitionsanchor="definitionforevc"> <name>Definitions from the EVC Standard</name><t>Access Unit: A<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 codedpicture.</t> <t>Adaptation parameter set (APS): Apicture.</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 sliceheaders.</t> <t>Bitstream: Aheaders.</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 morecoded video sequences (CVSs).</t> <t>Coded Picture: ACVSs.</dd> <dt>Coded Picture:</dt> <dd>A coded representation of a picture containing all CTUs of thepicture.</t> <t>Codedpicture.</dd> <dt>Coded Video Sequence(CVS): A(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 accessunit.</t> <t>Codingunit.</dd> <dt>Coding Tree Block(CTB): An(CTB):</dt> <dd>An NxN block of samples for some value of N such that the division of a component into CTBs is apartitioning.</t> <t>Codingpartitioning.</dd> <dt>Coding Tree Unit(CTU): A(CTU):</dt> <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 three separatecolourcolor planes and syntax structures used to code thesamples.</t> <t>Decoded Picture: Asamples.</dd> <dt>Decoded Picture:</dt> <dd>A decoded picture is derived by decoding a codedpicture.</t> <t>Decodedpicture.</dd> <dt>Decoded Picture Buffer(DPB): A(DPB):</dt> <dd>A buffer holding decoded pictures for reference, output reordering, or output delay specified for the hypothetical reference decoder in Annex C of the <xref target="EVC"/>standard.</t> <t>Dynamicstandard.</dd> <dt>Dynamic Range Adjustment(DRA): A(DRA):</dt> <dd>A mapping process that is applied to the decoded picture prior to cropping and output as part of the decodingprocess andprocess; it is controlled by parameters conveyed in an Adaptation Parameter Set(APS).</t> <t>Hypothetical(APS).</dd> <dt>Hypothetical Reference Decoder(HRD): A(HRD):</dt> <dd>A hypothetical decoder model that specifies constraints on the variability of conforming NAL unit streams or conforming byte streams that an encoding process mayproduce.</t> <t>IDR access unit:produce.</dd> <dt>IDR Access Unit:</dt> <dd>An access unit in which the coded picture is an IDRpicture.</t> <t>IDR picture:picture.</dd> <dt>IDR Picture:</dt> <dd>The coded picture for which each VCL NAL unit has NalUnitType equal toIDR_NUT.</t> <t>Level: AIDR_NUT.</dd> <dt>Level:</dt> <dd>A defined set of constraints on the values that may be taken by the syntax elements and variables of this document, or the value of a transform coefficient prior toscaling.</t> <t>Networkscaling.</dd> <dt>Network Abstraction Layer (NAL)unit: AUnit:</dt> <dd>A syntax structure containing an indication of the type of data to follow and bytes containing that data in the form of an RBSP interspersed asnecessary.</t> <t>Networknecessary.</dd> <dt>Network Abstraction Layer (NAL) UnitStream: AStream:</dt> <dd>A sequence of NALunits.</t> <t>Non-IDR Picture: Aunits.</dd> <dt>Non-IDR Picture:</dt> <dd>A coded picture that is not an IDRpicture.</t> <t>Non-VCLpicture.</dd> <dt>Non-VCL NALUnit: AUnit:</dt> <dd>A NAL unit that is not a VCL NALunit.</t> <t>Pictureunit.</dd> <dt>Picture Parameter Set(PPS): A(PPS):</dt> <dd>A syntax structure containing syntax elements that apply to zero or more entire coded pictures as determined by a syntax element found in each sliceheader.</t> <t>Pictureheader.</dd> <dt>Picture Order Count(POC): A(POC):</dt> <dd>A variable that is associated with each picture, uniquely identifies the associated picture among all pictures in the CVS,and, whenand (when the associated picture is to be output from thedecoded picture buffer,DPB) indicates 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 thedecoded picture buffer.</t> <t>RawDPB.</dd> <dt>Raw Byte Sequence Payload(RBSP): A(RBSP):</dt> <dd>A syntax structure containing an integer number of bytes that is encapsulated in a NAL unit and that is either empty or has the form of a string of data bits containing syntax elements followed by an RBSP stop bit and zero or more subsequent bits equal to0.</t> <t>Sequence0.</dd> <dt>Sequence Parameter Set(SPS): A(SPS):</dt> <dd>A syntax structure containing syntax elements that apply to zero or more entire CVSs as determined by the content of a syntax element found in the PPS referred to by a syntax element found in each sliceheader.</t> <t>Slice:header.</dd> <dt>Slice:</dt> <dd>An integer number of tiles of a picture in the tile scan of thepicture and that arepicture, exclusively contained in a single NALunit.</t> <t>Tile:unit.</dd> <dt>Tile:</dt> <dd>A rectangular region of CTUs within a particular tile column and a particular tile row in apicture.</t> <t>Tile column:picture.</dd> <dt>Tile Column:</dt> <dd>A rectangular region of CTUs having a height equal to the height of the picture and width specified by syntax elements in thePPS.</t> <t>Tile row: APPS.</dd> <dt>Tile Row:</dt> <dd>A rectangular region of CTUs having a height specified by syntax elements in the PPS and a width equal to the width of thepicture.</t> <t>Tile scan: Apicture.</dd> <dt>Tile Scan:</dt> <dd>A specific sequential ordering of CTUs partitioning a picture in which the CTUs are ordered consecutively in CTU raster scan in atiletile, whereas tiles in a picture are ordered consecutively in a raster scan of the tiles of thepicture.</t> <t>Video coding layerpicture.</dd> <dt>Video Coding Layer (VCL) NALunit: AUnit:</dt> <dd>A collective term for coded slice NAL units and the subset of NAL units that have reserved values of NalUnitType that are classified as VCL NAL units in thisdocument.</t>document.</dd> </dl> </section> <sectionanchor="def"><name>Definitionsanchor="def"> <name>Definitions Specific to This Document</name><t>Media-Aware<dl newline="true" spacing="normal"> <dt>Media-Aware Network Element(MANE): A(MANE):</dt><dd><t>A network element, such as a middlebox, selective forwarding unit, or application-layergatewaygateway, that is capable of parsing certain aspects of the RTP payload headers or the RTP payload and reacting to their contents.</t><ul empty="true"><li> <t>Informative<!-- [rfced] We used the <aside> element for Informative notes. Please review and let us know if any updates are needed. Note that the <aside> element is defined as "a container for content that is semantically less important or tangential to the content that surrounds it" (https://authors.ietf.org/en/rfcxml-vocabulary#aside). --> <aside><t>Informative note: The concept of a MANE goes beyond normal 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 media streams), and in that it has to be trusted when working with Secure RTP (SRTP). The advantage of using MANEs is that they allow packets to be dropped according to the needs of the media coding. For example, if a MANE has to drop packets due to congestion on a certain link, it can identify and remove those packets whose elimination produces the least adverse effect on the user experience. After dropping packets, MANEs must rewrite RTCP packets to match the changes to the RTP stream, as specified inSection 7 of<xreftarget="RFC3550"/>.</t> </li></ul> <t>NALtarget="RFC3550" section="7" sectionFormat="of"/>.</t></aside> </dd> <dt>NAL unit decodingorder: Aorder:</dt><dd>A NAL unit order that conforms to the constraints on NAL unit order given in Section 7.4.2.3inof <xreftarget="EVC"/>, followtarget="EVC"/> and follows the order of NAL units in thebitstream.</t> <t>NALU-time: Thebitstream.</dd> <dt>NALU-time:</dt><dd>The value that the RTP timestamp would have if the NAL unit would be transported in its own RTPpacket.</t> <t>NALpacket.</dd> <dt>NAL unit outputorder: Aorder:</dt><dd>A NAL unit order in which NAL units of different access units are in the output order of the decoded pictures corresponding to the access units, as specified in <xref target="EVC"/>, and in which NAL units within an access unit are in their decodingorder.</t> <t>RTP stream: Seeorder.</dd> <dt>RTP stream:</dt><dd>See <xref target="RFC7656"/>. Within the scope of this document, one RTP stream is utilized to transportaan EVC bitstream, which may contain one or more temporalsub-layers.</t> <t>Transmission order: Thesub-layers.</dd> <dt>Transmission order:</dt><dd>The order of packets in ascending RTP sequence number order (in modulo arithmetic). Within anaggregation packet,Aggregation Packet (AP), the NAL unit transmission order is the same as the order of appearance of NAL units in thepacket.</t>packet.</dd> </dl> </section> </section> <sectionanchor="abbreviations"><name>Abbreviations</name> <t>AU         Access Unit</t> <t>AP         Aggregation Packet</t> <t>APS        Adaptationanchor="abbreviations"> <name>Abbreviations</name> <dl newline="false" spacing="normal" indent="9"> <dt>AU</dt> <dd>Access Unit</dd> <dt>AP</dt> <dd>Aggregation Packet</dd> <dt>APS</dt> <dd>Adaptation ParameterSet</t> <t>ATS        AdaptiveSet</dd> <dt>ATS</dt> <dd>Adaptive TransformSelection</t> <t>B          Bi-predictive</t> <t>CBR        ConstantSelection</dd> <dt>B</dt> <dd>Bi-predictive</dd> <dt>CBR</dt> <dd>Constant BitRate</t> <t>CPB        CodedRate</dd> <dt>CPB</dt> <dd>Coded PictureBuffer</t> <t>CTB        CodingBuffer</dd> <dt>CTB</dt> <dd>Coding TreeBlock</t> <t>CTU        CodingBlock</dd> <dt>CTU</dt> <dd>Coding TreeUnit</t> <t>CVS        CodedUnit</dd> <dt>CVS</dt> <dd>Coded VideoSequence</t> <t>DPB        DecodedSequence</dd> <dt>DPB</dt> <dd>Decoded PictureBuffer</t> <t>HRD        HypotheticalBuffer</dd> <dt>HRD</dt> <dd>Hypothetical ReferenceDecoder</t> <t>HSS        HypotheticalDecoder</dd> <dt>HSS</dt> <dd>Hypothetical StreamScheduler</t> <t>I          Intra</t> <t>IDR        InstantaneousScheduler</dd> <dt>I</dt> <dd>Intra</dd> <dt>IDR</dt> <dd>Instantaneous DecodingRefresh</t> <t>LSB        LeastRefresh</dd> <dt>LSB</dt> <dd>Least SignificantBit</t> <t>LTRP       Long-TermBit</dd> <dt>LTRP</dt> <dd>Long-Term ReferencePicture</t> <t>MMVD       MergePicture</dd> <dt>MMVD</dt> <dd>Merge with Motion VectorDifference</t> <t>MSB        MostDifference</dd> <dt>MSB</dt> <dd>Most SignificantBit</t> <t>NAL        NetworkBit</dd> <dt>NAL</dt> <dd>Network AbstractionLayer</t> <t>P          Predictive</t> <t>POC        PictureLayer</dd> <dt>P</dt> <dd>Predictive</dd> <dt>POC</dt> <dd>Picture OrderCount</t> <t>PPS        PictureCount</dd> <dt>PPS</dt> <dd>Picture ParameterSet</t> <t>QP         Quantization Parameter</t> <t>RBSP       RawSet</dd> <dt>QP</dt> <dd>Quantization Parameter</dd> <dt>RBSP</dt> <dd>Raw Byte SequencePayload</t> <t>RGB        Same as GBR</t> <t>SAR        SamplePayload</dd> <dt>RGB</dt> <dd>Red, Green, and Blue</dd> <dt>SAR</dt> <dd>Sample AspectRatio</t> <t>SEI        SupplementalRatio</dd> <dt>SEI</dt> <dd>Supplemental EnhancementInformation</t> <t>SODB       StringInformation</dd> <dt>SODB</dt> <dd>String Of DataBits</t> <t>SPS        SequenceBits</dd> <dt>SPS</dt> <dd>Sequence ParameterSet</t> <t>STRP       Short-TermSet</dd> <dt>STRP</dt> <dd>Short-Term ReferencePicture</t> <t>VBR        VariablePicture</dd> <dt>VBR</dt> <dd>Variable BitRate</t> <t>VCL        VideoRate</dd> <dt>VCL</dt> <dd>Video CodingLayer</t>Layer</dd> </dl> </section> </section> <sectionanchor="RTPPayloadFormat"><name>RTPanchor="RTPPayloadFormat"> <name>RTP Payload Format</name> <sectionanchor="RTPHeaderUsage"><name>RTPanchor="RTPHeaderUsage"> <name>RTP Header Usage</name> <t>The format of the RTP header is specified in <xref target="RFC3550"/>(reprinted(included as <xref target="rtp-header"/> for convenience). This payload format uses the fields of the header in a manner consistent with that specification.</t> <t>The RTP payload (and the settings for some RTP header bits) foraggregation packetsAPs andfragmentation unitsFragmentation Units (FUs) are specified in Sections <xreftarget="aps"/>target="aps" format="counter"/> and <xreftarget="funits"/>,target="funits" format="counter"/>, respectively.</t> <figureanchor="rtp-header"><sourcecode type="~"><![CDATA[anchor="rtp-header"> <name>RTP Header According to RFC 3550</name> <artwork><![CDATA[ 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |V=2|P|X| CC |M| PT | sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | timestamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | synchronization source (SSRC) identifier | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | contributing source (CSRC) identifiers | | .... |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ RTP Header According to [RFC3550] ]]></sourcecode></figure>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork> </figure> <t>The RTP header information to be set according to this RTP payload format is set as follows:</t><t>Marker<dl newline="false" spacing="normal"> <dt>Marker bit(M): 1(M):</dt> <dd><t>1 bit</t><ul empty="true"><li><t>Set for the last packet of the accessunit,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></li></ul> <t>Payload</dd> <dt>Payload Type(PT): 7(PT):</dt> <dd><t>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</dd> <dt>Sequence Number(SN): 16(SN):</dt> <dd><t>16 bits</t><ul empty="true"><li><t>Set and used in accordance with <xref target="RFC3550"/>.</t></li></ul> <t>Timestamp: 32</dd> <dt>Timestamp:</dt> <dd><t>32 bits</t><ul empty="true"><li><t>The RTP timestamp is set to the sampling timestamp of the content. A 90 kHz clock rateMUST<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 timestampMUST<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"/>. ReceiversMUST<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></li></ul> <t>Synchronization</dd> <dt>Synchronization source(SSRC): 32(SSRC):</dt> <dd><t>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></dd> </dl> </section> <sectionanchor="PayloadHeaderUsage"><name>Payloadanchor="PayloadHeaderUsage"> <name>Payload Header Usage</name> <t>The first two bytes of the payload of an RTP packet are referred to as the payload header. The payload header consists of the same fields (F, TID,ReserveReserve, and E) as the NAL unitheaderheader, 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 TIDvaluevalues are not usedfor the decoding ofto decode the ones with smaller TIDvalue.values. A lower value of TID indicates a higher importance.More-importantMore important NAL unitsMAY<bcp14>MAY</bcp14> be better protected against transmission losses thanless-importantless important NAL units.</t> </section> <sectionanchor="PayloadStructures"><name>Payloadanchor="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 field in the payload header.</t> <t>The three different payload structures are as follows:</t><t><list style="symbols"> <t>Single<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 <xreftarget="SingleNALUnit"/>.</t> <t>Aggregationtarget="SingleNALUnit"/>.</li> <li>Aggregation Packet (AP): Contains more than one NAL unit within one access unit. This payload structure is specified in <xreftarget="aps"/>.</t> <t>Fragmentationtarget="aps"/>.</li> <li>Fragmentation Unit (FU): Contains a subset of a single NAL unit. This payload structure is specified in <xreftarget="funits"/>.</t> </list></t>target="funits"/>.</li> </ul> <sectionanchor="SingleNALUnit"><name>Singleanchor="SingleNALUnit"> <name>Single NAL Unit Packets</name> <t>A single NAL unit packet contains exactly one NALunit,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> <figureanchor="single-nhr"><artwork><![CDATA[anchor="single-nhr"> <name>The Structure of a Single NAL Unit Packet</name> <artwork><![CDATA[ 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PayloadHdr | DONL (conditional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | NAL unit payload data | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | :...OPTIONAL RTP padding |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Structure of a Single NAL Unit Packet ]]></artwork></figure>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></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 <xreftarget="optionalParameters"/>target="optionalParameters"/>) is greater than 0, the DONL fieldMUST<bcp14>MUST</bcp14> be present, and the variable DON for the contained NAL unit is derived as equal to the value of the DONL field. Otherwise(sprop-max-don-diff(where sprop-max-don-diff is equal to 0), the DONL fieldMUST NOT<bcp14>MUST NOT</bcp14> be present.</t> </section> <sectionanchor="aps"><name>Aggregationanchor="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 few octets in size.</t> <t>An AP aggregates NAL units of one access unit, and itMUST NOT<bcp14>MUST NOT</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 withType=56)Type=56), followed by two or more aggregation units, as shown in <xref target="au-hdr"/>.</t> <figureanchor="au-hdr"><artwork><![CDATA[anchor="au-hdr"> <name>The Structure of an Aggregation Packet</name> <artwork><![CDATA[ 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PayloadHdr (Type=56) | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | two or more aggregation units | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | :...OPTIONAL RTP padding |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Structure of an Aggregation Packet ]]></artwork></figure>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork> </figure> <t>The fields in the payload header of an AP are set as follows. The F bitMUST<bcp14>MUST</bcp14> be equal to 0 if the F bit of each aggregated NAL unit is equal to zero; otherwise, itMUST<bcp14>MUST</bcp14> be equal to 1. The Type fieldMUST<bcp14>MUST</bcp14> be equal to 56.</t> <t>The value of TIDMUST<bcp14>MUST</bcp14> be the smallest value of TID of all the aggregated NAL units. The value of Reserve and EMUST<bcp14>MUST</bcp14> be equal to 0 for this specification.</t><ul empty="true"><li> <t>Informative<aside><t>Informative note: All VCL NAL units in an AP have the same TID value since they belong to the same access unit. However, an AP may contain non-VCL NAL units for which the TID value in the NAL unit header may be different from the TID value of the VCL NAL units in the sameAP.</t> </li></ul>AP.</t></aside> <t>An APMUST<bcp14>MUST</bcp14> carry at least two aggregation units and can carry as many aggregation units as necessary; however, the total amount of data in an AP obviouslyMUST<bcp14>MUST</bcp14> fit into an IP packet, and the sizeSHOULD<bcp14>SHOULD</bcp14> be chosen so that the resulting IP packet is smaller than the path MTU size so to avoid IP layer fragmentation. An APMUST NOT<bcp14>MUST NOT</bcp14> contain FUs specified in <xref target="funits"/>. APsMUST NOT<bcp14>MUST NOT</bcp14> be nested; i.e., an APcan notcannot contain another AP.</t><ul empty="true"><li> <t>Informative<aside><t>Informative note: If a receiver encounters nestedAggregation Packets,APs, which is against the aforementioned requirement, it has several options, listed in order of ease of implementation: 1)Ignoreignore the nested AP; 2)Ignoreignore the nested AP and report a"packet loss""packet loss" to the decoder, if such functionality exists in theAPI,API; and 3)Implementimplement support for nested APs and extract theNetwork Abstraction Layer (NAL)NAL units from these nestedAPs.</t> </li></ul>APs.</t></aside> <t>The first aggregation unit in an AP consists of a conditional 16-bit DONL field (in network byte order) followed by a 16-bit unsigned size information (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 <xref target="au-first-nhdr"/>.</t> <figureanchor="au-first-nhdr"><artwork><![CDATA[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 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NALU size | | +-+-+-+-+-+-+-+-+ NAL unit | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | :+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Structure of the First Aggregation Unit in an AP ]]></artwork></figure> <ul empty="true"><li> <t>Informative+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork> </figure> <aside><t>Informative note: The first octet of <xref target="au-first-nhdr"/> (indicated by the first colon) belongs to a previous aggregation unit. It is depicted to emphasize that aggregation units are octet aligned only. Similarly, the NAL unit carried in the aggregation unit can terminate at the octetboundary.</t> </li></ul>boundary.</t></aside> <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 fieldMUST<bcp14>MUST</bcp14> be present in an aggregation unit that is the first aggregation unit in an AP. The variable DON for the aggregated NAL unit is derived as equal to the value of the DONL field, and the variableDONDecoding Order Number (DON) for an aggregation unit that is not the first aggregation unit in an AP-aggregated NAL unit is derived as equal to the DON of the preceding aggregated NAL unit in the same AP plus 1 modulo 65536. Otherwise(sprop-max-don-diff(where sprop-max-don-diff is equal to 0), the DONL fieldMUST NOT<bcp14>MUST NOT</bcp14> be present in an aggregation unit that is the first aggregation unit in anAP</t>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 two octets but including the NAL unit header), followed by the NAL unit itself, including its NAL unit header, as shown in <xref target="au-not-first-nhdr"/>.</t> <figureanchor="au-not-first-nhdr"><artwork><![CDATA[anchor="au-not-first-nhdr"> <name> The Structure of an Aggregation Unit That Is Not the First Aggregation Unit in an AP</name> <artwork><![CDATA[ 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | : NALU size | NAL unit | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | :+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Structure of an Aggregation Unit That Is Not the First Aggregation Unit in an AP ]]></artwork></figure> <ul empty="true"><li> <t>Informative+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork> </figure> <aside><t>Informative note: The first octet of <xref target="au-not-first-nhdr"/> (indicated by the first colon) belongs to a previous aggregation unit. It is depicted to emphasize that aggregation units are octet aligned only. Similarly, the NAL unit carried in the aggregation unit can terminate at the octetboundary.</t> </li></ul>boundary.</t></aside> <t><xref target="au-wout-donl"/> presents an example of an AP that contains two aggregation units, labeledas NALU 1"NALU 1" andNALU 2 in the figure,"NALU 2", without the DONL field being present.</t> <figureanchor="au-wout-donl"><artwork><![CDATA[anchor="au-wout-donl"> <name>An Example of an AP Packet Containing Two Aggregation Units without the DONL Field</name> <artwork><![CDATA[ 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RTP Header | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PayloadHdr (Type=56) | NALU 1 Size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NALU 1 HDR | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NALU 1 Data | | . . . | | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . . . | NALU 2 Size | NALU 2 HDR | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NALU 2 HDR | | +-+-+-+-+-+-+-+-+ NALU 2 Data | | . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | :...OPTIONAL RTP padding |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ An Example of an AP Packet Containing Two Aggregation Units without the DONL Field ]]></artwork></figure>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork> </figure> <t><xref target="au-with-donl"/> presents an example of an AP that contains two aggregation units, labeledas NALU 1"NALU 1" andNALU 2 in the figure,"NALU 2", with the DONL field being present.</t> <figureanchor="au-with-donl"><artwork><![CDATA[anchor="au-with-donl"> <name>An Example of an AP Containing Two Aggregation Units with the DONL Field</name> <artwork><![CDATA[ 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RTP Header | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PayloadHdr (Type=56) | NALU 1 DONL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NALU 1 Size | NALU 1 HDR | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | NALU 1 Data . . . | | | + . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | : NALU 2 Size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NALU 2 HDR | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NALU 2 Data | | | | . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | :...OPTIONAL RTP padding |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ An Example of an AP Containing Two Aggregation Units with the DONL Field ]]></artwork></figure>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork> </figure> </section> <sectionanchor="funits"><name>Fragmentation Units</name> <t>Fragmentationanchor="funits"> <name>Fragmentation Units(FUs)(FUs)</name> <t>FUs are introduced to enable fragmenting a single NAL unit 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 consecutive octets of that NAL unit. Fragments of the same NAL unitMUST<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 referred to as a fragmented NAL unit. APsMUST NOT<bcp14>MUST NOT</bcp14> be fragmented. FUsMUST NOT<bcp14>MUST NOT</bcp14> 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"/> (denoted as PayloadHdr withtype=57),Type=57), an FU header of one octet, a conditional 16-bit DONL field (in network byte order), and an FU payload, as shown in <xref target="fu-payload"/>.</t> <figureanchor="fu-payload"><artwork><![CDATA[anchor="fu-payload"> <name>The Structure of an FU</name> <artwork><![CDATA[ 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PayloadHdr (Type=57) | FU header | DONL (cond) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | DONL (cond) | | |-+-+-+-+-+-+-+-+ | | FU payload | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | :...OPTIONAL RTP padding |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Structure of an FU ]]></artwork></figure>+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork> </figure> <t>The fields in the payload header are set as follows. The Type fieldMUST<bcp14>MUST</bcp14> be equal to 57. The fields F, TID,ReserveReserve, and EMUST<bcp14>MUST</bcp14> be equal to the fields F, TID,ReserveReserve, 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 shown in <xref target="fu-header"/>.</t> <figureanchor="fu-header"><artwork><![CDATA[anchor="fu-header"> <name>The Structure of FU Header</name> <artwork><![CDATA[ 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |S|E| FuType |+---------------+ The Structure of FU Header ]]></artwork></figure>+---------------+]]></artwork> </figure> <t>The semantics of the FU header fields are as follows:</t><t>S: 1<dl> <dt>S:</dt> <dd> <t>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 bitMUST<bcp14>MUST</bcp14> be set to 0.</t></li></ul> <t>E: 1</dd> <dt>E:</dt> <dd> <t>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 bitMUST<bcp14>MUST</bcp14> be set to 0.</t></li></ul> <t>FuType: 6</dd> <dt>FuType:</dt> <dd> <t>6 bits</t><ul empty="true"><li><t>The field FuTypeMUST<bcp14>MUST</bcp14> be equal to the field Type of the fragmented NAL unit.</t></li></ul></dd> </dl> <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 than0,0 and the S bit is equal to 1, the DONL fieldMUST<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(sprop-max-don-diff(where sprop-max-don-diff is equal to 0, or where the S bit is equal to 0), the DONL fieldMUST NOT<bcp14>MUST NOT</bcp14> be present in the FU.</t> <t>A non-fragmented NAL unitMUST NOT<bcp14>MUST NOT</bcp14> be transmitted in one FU; i.e., theStart bitS-bit andEnd bit MUST NOTE-bit <bcp14>MUST NOT</bcp14> both be set to 1 in the same FU header.</t> <t>The FU payload consists of fragments of the payload of the fragmented NAL unit so that if the FU payloads of consecutive FUs, starting with an FU with the S bit equal to 1 and ending with an FU with the E bit equal to 1, are sequentially 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 FUpayload, but ratherpayload. Instead, the information of the NAL unit header of the fragmented NAL unit is conveyed in F, TID,ReserveReserve, and E fields of the FU payload headers of the FUs and the FuType field of the FU header of the FUs. An FU payloadMUST NOT<bcp14>MUST NOT</bcp14> be empty.</t> <t>If an FU is lost, the receiverSHOULD<bcp14>SHOULD</bcp14> discard all following fragmentation units in transmission order corresponding to the same fragmented 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 MANEMAY<bcp14>MAY</bcp14> aggregate the first n-1 fragments of a NAL unit to an (incomplete) NAL unit, even if fragment n of that NAL unit is not received. In this case, the forbidden_zero_bit of the NAL unitMUST<bcp14>MUST</bcp14> be set to 1 to indicate a syntax violation.</t> </section> </section> <sectionanchor="DON"><name>Decodinganchor="DON"> <name>Decoding Order Number</name> <t>For each NAL unit, the variable AbsDon isderived, representingderived; it represents the decoding order number that is indicative of the NAL unit decoding order.</t> <t>Let NAL unit n be the n-th NAL unit in transmission order within an RTP stream.</t> <t>If sprop-max-don-diff is equal to 0,AbsDon[n], thethen AbsDon[n] (the value of AbsDon for NAL unitn,n) is derived as equal to n.</t> <t>Otherwise(sprop-max-don-diff(where sprop-max-don-diff is greater than 0), AbsDon[n] is derived as follows, where DON[n] is the value of the variable DON for NAL unit n:</t><t><list style="symbols"> <t>If<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 toDON[0].</t> <t>Otherwise (nDON[0].</li> <li><t>Otherwise (where n is greater than 0), the following applies for derivation of AbsDon[n]:</t></list></t> <figure><artwork><![CDATA[<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>]]></artwork></li> </ul> <t>For any two NAL unitsm(m andn,n), the following applies:</t><t><list style="symbols"> <t>AbsDon[n]<ul spacing="normal"> <li>When AbsDon[n] is greater thanAbsDon[m] indicates thatAbsDon[m], the NAL unit n follows NAL unit m in NAL unit decodingorder.</t> <t>Whenorder.</li> <li>When AbsDon[n] is equal to AbsDon[m], the NAL unit decoding order of the two NAL units can be in eitherorder.</t> <t>AbsDon[n]order.</li> <li>When AbsDon[n] is less thanAbsDon[m] indicates thatAbsDon[m], the NAL unit n precedes NAL unit m in decodingorder. <vspace blankLines='1'/> <ul empty="true"><li> <ul empty="true"><li> <t>Informativeorder.</li> </ul> <aside><t>Informative note: When two consecutive NAL units in the NAL unit decoding order has different values of AbsDon, thetheabsolute difference between the two AbsDon values may be greater than or equal to1.</t> </li></ul> </li></ul> <vspace blankLines='1'/> <ul empty="true"><li> <ul empty="true"><li> <t>Informative1.</t></aside> <aside><t>Informative note: There are multiple reasons to allowforthe 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 notrequired,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 aretransmitted,transmitted and gaps in the values of AbsDon mayoccur.</t> </li></ul> </li></ul> </t> </list></t>occur.</t></aside> </section> </section> <sectionanchor="PacketizationRules"><name>Packetizationanchor="PacketizationRules"> <name>Packetization Rules</name> <t>The following packetization rules apply:</t><t><list style="symbols"> <t>If<ul spacing="normal"> <li>If sprop-max-don-diff is greater than 0, the transmission order of NAL units carried in the RTP streamMAY<bcp14>MAY</bcp14> be different from the NAL unit decoding order. Otherwise(sprop-max-don-diff(where sprop-max-don-diff equals 0), the transmission order of NAL units carried in the RTP streamMUST<bcp14>MUST</bcp14> be the same as the NAL unit decodingorder.</t> <t>Aorder.</li> <li>A NAL unit of small sizeSHOULD<bcp14>SHOULD</bcp14> be encapsulated in anaggregation packetAP 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 sizeconstraints.</t> <t>Eachconstraints.</li> <li>Each non-VCL NAL unitSHOULD,<bcp14>SHOULD</bcp14>, when possible from an MTU size match viewpoint, be encapsulated in anaggregation packetAP with its associated VCL NALunit, asunit as, typically, a non-VCL NAL unit would be meaningless without the associated VCL NAL unit beingavailable.</t> <t>Foravailable.</li> <li>A single NAL unit packet <bcp14>MUST</bcp14> be used for carrying precisely one NAL unit in an RTPpacket, a single NAL unit packet MUST be used.</t> </list></t>packet.</li> </ul> </section> <sectionanchor="DepacketizationProcess"><name>De-packetizationanchor="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 unit decoding order.</t> <t>The de-packetization process is implementation dependent. Therefore, the following description should be seen as an example of a suitable implementation. Other 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 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 particular, duplicated or outdated RTP packets (as indicated by the RTP sequence number and the RTP timestamp) are removed. <!-- [rfced] FYI - To avoid repetition in the phrase "factors ... MUST be factored in", we updated to "factors ... MUST be considered". Please let us know if there is objection. Original: To determine the exact time for decoding, factors such as a possible intentional delay to allow for proper inter-stream synchronization, MUST be factoredin.</t>in. Current: To determine the exact time for decoding, factors such as a possible intentional delay to allow for proper inter-stream synchronization, MUST be considered. --> To determine the exact time for decoding, factors such as a possible intentional delay to allow for proper inter-stream synchronization 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 values in the range of 56 to 62, inclusive,MUST NOT<bcp14>MUST NOT</bcp14> be passed to the decoder.</t> <t>The receiver includes a receiver buffer, which is used to compensate for transmission delay jitter within individual RTP streams and to reorder NAL units from transmission order to the NAL unit decoding order. In this section, the receiver operation is described under the assumption that there is no transmission delay jitter within an RTP stream. To clarify the distinction from a practical receiver buffer, which is also used to compensate for transmission delay jitter, the buffer in this section will henceforth be referred to as thede-packetization"de-packetization" buffer. Receivers should also prepare for transmission delay jitter; that is, either reserve separate buffers for transmission delay jitter buffering and de-packetizationbufferingbuffering, 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 before startingofdecoding and playback.</t> <t>The de-packetization process extracts the NAL units from the RTP packets in an RTP stream as follows. When an RTP packet carries a single NAL unit packet, the payload of the RTP packet is extracted as a single NAL unit, excluding the DONL field, i.e., third and fourth bytes, when sprop-max-don-diff is greater than 0. When an RTP packet carries anaggregation packet,AP, several NAL units are extracted 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 field, as described in <xref target="aps"/>. When an RTP packet carries a Fragmentation 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 equal the values of the fields F and TID in the payload header of the FUs, respectively, 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 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 decoding 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-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 packets are stored in the de-packetization buffer individually, and the value of AbsDon is calculated and stored for each NAL unit.</t> <t>Initial buffering lasts until the difference between the greatest and smallest 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 smallest AbsDon values of the NAL units in the de-packetization buffer is greater than or equal to the value of sprop-max-don-diff, the following operation is repeatedly applied until this difference is smaller than sprop-max-don-diff:</t><t><list style="symbols"> <t>The<t indent="3">The NAL unit in the de-packetization buffer with the smallest value of AbsDon 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 passed to the decoder in the order of increasing AbsDon values.</t> <!-- Section 7 --> </section> <sectionanchor="PayloadFormatParameters"><name>Payloadanchor="PayloadFormatParameters"> <name>Payload Format Parameters</name> <t>This section specifies the optional parameters. A mapping of the parameters with the Session Description Protocol (SDP) <xref target="RFC8866"/> is also provided for applications that use SDP.</t> <t>Parameters starting with the string"sprop""sprop" for stream properties can be used by a sender to provide a receiver with the properties of the stream that is or will be sent. The media sender (and not the receiver) selects whether, and with what values,"sprop""sprop" parameters are being sent. This uncommon characteristic of the"sprop""sprop" parameters may not be intuitive in the context of some signaling protocol concepts, especially withoffer/answer.Offer/Answer. Please see <xref target="sdpoa"/> for guidance specific to the use of sprop parameters in the Offer/Answer case.</t> <!-- Section 7.1 --> <sectionanchor="oparams"><name>Mediaanchor="oparams"> <name>Media Type Registration</name> <t>The receiverMUST<bcp14>MUST</bcp14> ignore any parameter unspecified in this document.</t><t>Type name:            video</t> <t>Subtype name:         evc</t> <t>Required parameters: N/A</t> <t>Optional parameters: profile-id,<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"/> fordefinitions)</t> <t>Encoding considerations:</t> <ul empty="true"><li> <t>Thisdefinitions)</dd> <dt>Encoding considerations:</dt> <dd>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="RFC3550" format="default"/>.</dd> <dt>Security considerations:</dt> <dd>See <xref target="Security"/> of RFCXXXX.</t> </li></ul> <t>Interoperability considerations: N/A</t> <t>Published specification:</t> <ul empty="true"><li> <t>Please9584.</dd> <dt>Interoperability considerations:</dt><dd>N/A</dd> <dt>Published specification:</dt> <dd>Please refer to RFCXXXX9584 and EVC standard <xreftarget="EVC"/>.</t> </li></ul> <t>Applicationstarget="EVC"/>.</dd> <dt>Applications that use this mediatype:</t> <ul empty="true"><li> <t>Anytype:</dt> <dd>Any application that relies on EVC-based video services overRTP</t> </li></ul> <t>FragmentRTP</dd> <dt>Fragment identifierconsiderations: N/A</t> <t>Additional information: N/A</t> <t>Personconsiderations:</dt><dd>N/A</dd> <dt>Additional information:</dt><dd>N/A</dd> <dt>Person & email address to contact for furtherinformation:</t> <ul empty="true"><li> <t>Stephaninformation:</dt> <dd><br/>Stephan Wenger(stewe@stewe.org)</t> </li></ul> <t>Intended usage: COMMON</t> <t>Restrictions(stewe@stewe.org)</dd> <dt>Intended usage:</dt><dd>COMMON</dd> <dt>Restrictions onusage: N/A</t> <t>Author: See Authors'usage:</dt><dd>N/A</dd> <dt>Author:</dt><dd>See Authors' Addresses section of RFCXXXX.</t> <t>Change controller:</t> <ul empty="true"><li> <t>IETF <avtcore@ietf.org></t> </li></ul> <!-- Section 7.2 -->9584.</dd> <dt>Change controller:</dt> <dd>IETF <avtcore@ietf.org></dd> </dl> </section> <sectionanchor="optionalParameters"><name>Optionalanchor="optionalParameters"> <name>Optional Parameters Definition</name><t>profile-id,<dl newline="true"> <dt>profile-id, level-id,toolset-id:</t> <ul empty="true"><li> <t>Thesetoolset-id:</dt> <dd><t>These parameters indicate the profile, the level, and constraints of the bitstream carried by the RTPstream,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 syntax elements specified in <xref target="EVC"/> are provided below.</t></li></ul> <t>profile-id:</t> <ul empty="true"><li> <t>When</dd> <dt>profile-id:</dt> <dd><t>When profile-id is not present, a value of 0 (i.e., the Baseline profile)MUST<bcp14>MUST</bcp14> be inferred.</t></li></ul> <ul empty="true"><li><t>When used to indicate properties of a bitstream, profile-idMUST<bcp14>MUST</bcp14> 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 documentSHOULD<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 (forexampleexample, 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 StillPicturepicture 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</dd> <dt>level-id:</dt> <dd><t>When level-id is not present, a value of 90 (corresponding to level 3, which allows for approximatelySD TVstandard-definition television (SD TV) resolution and frame rates;for details pleasesee Annex A ofEVC) MUST<xref target="EVC"/>) <bcp14>MUST</bcp14> be inferred.</t></li></ul> <ul empty="true"><li><t>When used to indicate properties of a bitstream, level-idMUST<bcp14>MUST</bcp14> be derived from 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 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 supportedMUST<bcp14>MUST</bcp14> also be supported.</t></li></ul> <t>toolset-id:</t> <ul empty="true"><li> <t>This</dd> <dt>toolset-id:</dt> <dd>This parameter is abase64 encoding (Section 4 of <xref target="RFC4648"></xref>)base64-encoding representation (<xref target="RFC4648" section="4" sectionFormat="of"/>) of a64 bit64-bit unsigned integer bit mask derived from the concatenation, in network byte order, of the syntax elements toolset_idc_h and toolset_idc_l. When used to indicate properties of a bitstream, its valueMUST<bcp14>MUST</bcp14> be derived from toolset_idh_h and toolset_idc_l in the sequence parameterset.</t> </li></ul> <t>max-recv-level-id:</t> <ul empty="true"><li> <t>Thisset.</dd> <dt>max-recv-level-id:</dt> <dd><t>This parameterMAY<bcp14>MAY</bcp14> be used to indicate the highest level a receiver supports.</t></li></ul><t>The value of max-recv-level-idMUST<bcp14>MUST</bcp14> be in the range of 0 to 255,inclusive.P.</t>inclusive.</t> <t>When max-recv-level-id is not present, the value is inferred to be equal to level-id.</t> <t>max-recv-level-idMUST NOT<bcp14>MUST NOT</bcp14> be present when the highest level the receiver supports is not higher than the defaultlevel.</t> <t>sprop-sps:</t> <ul empty="true"><li> <t>Thislevel.</t></dd> <dt>sprop-sps:</dt> <dd><t>This parameterMAY<bcp14>MAY</bcp14> be used to convey sequence parameter set NAL units of the bitstream for out-of-band transmission of sequence parameter sets. The value of the parameter is a comma-separated(',')(',') list ofbase64 encoding (Section 4 of <xref target="RFC4648"/>)base64-encoding representations (<xref 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></li></ul> <t>sprop-pps:</t> <ul empty="true"><li> <t>This</dd> <dt>sprop-pps:</dt> <dd><t>This parameterMAY<bcp14>MAY</bcp14> 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 ofbase64 encoding (Section 4 of <xref target="RFC4648"/>)base64-encoding representations (<xref target="RFC4648" section="4" sectionFormat="of"/>) of the picture parameter set NAL units as specified in Section 7.3.2.2 of <xreftarget="EVC"/>.</t> </li></ul> <t>sprop-sei:</t> <ul empty="true"><li> <t>Thistarget="EVC"/>.</t></dd> <dt>sprop-sei:</dt> <dd><t>This parameterMAY<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></li></ul> <ul empty="true"><li><t>The value of the parameter is a comma-separated(',')(',') list ofbase64 encoding (Section 4 of <xref target="RFC4648"/>)base64-encoding representations (<xref target="RFC4648" section="4" sectionFormat="of"/>) of SEI NAL units as specified in <xref target="VSEI"/>.</t></li></ul> <ul empty="true"><li> <ul empty="true"><li> <t>Informative<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, afewcouple of examples are describedbelow:</t> </li></ul> </li></ul> <ul empty="true"><li> <ul empty="true"><li> <t>1) Inbelow.</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 likelymeaningful,meaningful; and sending it in sprop-sei rather than in the bitstream at each entry point may help with saving bits andallowsallow one to configure the renderer only once, avoiding unwantedartifacts.</t> </li></ul> </li></ul> <ul empty="true"><li> <ul empty="true"><li> <t>2) Examplesartifacts.</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 inSDP).</t> </li></ul> </li></ul> <t>sprop-max-don-diff:</t> <ul empty="true"><li> <t>IfSDP).</li> </ol></aside> </dd> <dt>sprop-max-don-diff:</dt> <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 parameterMUST<bcp14>MUST</bcp14> 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 transmission order.</t></li></ul> <ul empty="true"><li><t>The value of sprop-max-don-diffMUST<bcp14>MUST</bcp14> be an integer in the range of 0 to 32767, inclusive.</t></li></ul> <ul empty="true"><li><t>When not present, the value of sprop-max-don-diff is inferred to be equal to 0.</t></li></ul> <t>sprop-depack-buf-bytes:</t> <ul empty="true"><li></dd> <dt>sprop-depack-buf-bytes:</dt> <dd> <t>This parameter signals the required size of the de-packetization buffer in units of bytes. The value of the parameterMUST<bcp14>MUST</bcp14> be greater than or equal to the maximum buffer occupancy (in units of bytes) of the de-packetization buffer as specified inSection 6.</t> </li></ul> <ul empty="true"><li><xref target="DepacketizationProcess" format="default"/>.</t> <t>The value of sprop-depack-buf-bytesMUST<bcp14>MUST</bcp14> 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 parameterMUST<bcp14>MUST</bcp14> be present and the valueMUST<bcp14>MUST</bcp14> 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> <ul empty="true"><li> <t>Informative<aside><t>Informative note: The value of sprop-depack-buf-bytes indicates the required size of the de-packetization buffer only. When network jitter can occur, an appropriately sized jitter buffer has to be available aswell.</t> </li></ul> </li></ul> <t>depack-buf-cap:</t> <ul empty="true"><li>well.</t></aside> </dd> <dt>depack-buf-cap:</dt> <dd> <t>This parameter signals the capabilities of a receiver 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></li></ul> <ul empty="true"><li><t>When not present, the value of depack-buf-cap is inferred to be equal to 4294967295. The value of depack-buf-capMUST<bcp14>MUST</bcp14> be an integer in the range of 1 to 4294967295, inclusive.</t></li></ul> <ul empty="true"><li> <ul empty="true"><li> <t>Informative<!-- [rfced] To match the informative note above this one, may we update "depack-buf-cap indicates" to "The value of depack-buf-cap indicates"? Previous Informative note: | Informative note: The value of sprop-depack-buf-bytes | indicates the required size of the de-packetization buffer | only. When network jitter can occur, an appropriately sized | jitter buffer has to be available as well. Original: Informative note: depack-buf-cap indicates the maximum possible size of the de-packetization buffer of the receiver only, without allowing for networkjitter.</t> </li></ul> </li></ul> <!-- Section 7.3jitter. Perhaps: | 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. --> <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> <sectionanchor="sdp-parameters"><name>SDPanchor="sdp-parameters"> <name>SDP Parameters</name> <t>The receiverMUST<bcp14>MUST</bcp14> ignore any parameter unspecified in this document.</t> <!-- Section 7.3.1 --> <sectionanchor="mapping-of-payload-type-parameters-to-sdp"><name>Mappinganchor="mapping-of-payload-type-parameters-to-sdp"> <name>Mapping of Payload Type Parameters to SDP</name> <t>The media type video/evc string is mapped to fields in the Session Description Protocol (SDP) <xref target="RFC8866"/> as follows:</t><t><list style="symbols"> <t>The<ul spacing="normal"> <li>The media name in the"m=""m=" line of SDPMUST<bcp14>MUST</bcp14> bevideo.</t> <t>Thevideo.</li> <li>The encoding name in the"a=rtpmap""a=rtpmap" line of SDPMUST<bcp14>MUST</bcp14> be evc (the mediasubtype).</t> <t>Thesubtype).</li> <li>The clock rate in the"a=rtpmap""a=rtpmap" lineMUST<bcp14>MUST</bcp14> be90000.</t> <t>The90000.</li> <!-- [rfced] Should "fmtp" be "a=fmtp"? Original (first sentence included for context): * The OPTIONAL parameters profile-id, level-id, toolset-id,max-recv-level-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""a=fmtp" line of SDP. The fmtp line is expressed as a media type string, in the form of a semicolon-separated list of parameter=valuepairs.</t> <t>The OPTIONALpairs. --> <li>The <bcp14>OPTIONAL</bcp14> 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, <bcp14>MUST</bcp14> be included in the "a=fmtp" line of SDP. The "fmtp" line is expressed as a media type string, in the form of a semicolon-separated list of parameter=value pairs.</li> <li>The <bcp14>OPTIONAL</bcp14> parameters sprop-sps, sprop-pps, and sprop-sei, when present,MUST<bcp14>MUST</bcp14> be included in the"a=fmtp""a=fmtp" line of SDP or conveyed using the"fmtp""fmtp" source attribute as specified inSection 6.3 of<xreftarget="RFC5576"/>.target="RFC5576" sectionFormat="of" section="6.3"/>. For a particular media format (i.e., RTP payload type), sprop-sps, sprop-pps, or sprop-seiMUST NOT<bcp14>MUST NOT</bcp14> be both included in the"a=fmtp""a=fmtp" line of SDP and conveyed using the"fmtp""fmtp" source attribute. When included in the"a=fmtp""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""a=fmtp" line of SDP for a particular payload type, the parameters sprop-sps, sprop-pps, and sprop-seiMUST<bcp14>MUST</bcp14> be applied to each SSRC with the payload type. When conveyed using the"fmtp""fmtp" source attribute, these parameters are only associated with the given source and payload type as parts of the"fmtp""fmtp" sourceattribute.</t> </list></t> <ul empty="true"><li> <t>Informativeattribute.</li> </ul> <aside><t>Informative note: Conveyance of sprop-sps and sprop-pps using the"fmtp""fmtp" source attribute allows for out-of-band transport of parameter sets in topologies like Topo-Video-switch-MCU, as specified in <xreftarget="RFC7667"/>.</t> </li></ul>target="RFC7667"/>.</t></aside> <t>A general usage of media representation in SDP is as follows:</t><figure><artwork><![CDATA[<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]]></artwork> <!-- [rfced] We believe SIP is correct, but please confirm that "SIP" is intended, as it is the only occurrence in the document. Original: A SIP offer/answer exchange wherein both parties are expected to both send and receive could look like the following. --> <t>A SIP Offer/Answer exchange wherein both parties are expected to both send and receive could look like the following. Only the media codec-specific parts of the SDP are shown.</t><figure><artwork><![CDATA[<artwork><![CDATA[ Offerer->Answerer: m=video 49170 RTP/AVP 98 a=rtpmap:98 evc/90000 a=fmtp:98 profile-id=1; level_id=90;]]></artwork></figure> <ul empty="true"><li>]]></artwork> <t>The above represents an offer for symmetric video communication using <xref target="EVC"/> and its payload specification at the main profile and level3.0.3. 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","as is", the offer can expect that theanswererAnswerer would be able to receive and properly decode EVC media up to and including level3.0.</t> </li></ul> <figure><artwork><![CDATA[3.</t> <artwork><![CDATA[ Answerer->Offerer: m=video 49170 RTP/AVP 98 a=rtpmap:98 evc/90000 a=fmtp:98 profile-id=1; level_id=60]]></artwork></figure> <ul empty="true"><li> <ul empty="true"><li> <t>Informative]]></artwork> <aside><t>Informative note: level_id shall be set equal to a value of 30 times the level number specified in Table A.1 ofEVC.</t> </li></ul> </li></ul><xref target="EVC"/>.</t></aside> <t>With this answer to the offer above, the system receiving the offer advises theoffererOfferer that it is incapable ofhandinghandling evc at level3.03 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 7.3.2 --></section> <sectionanchor="sdpoa"><name>Usageanchor="sdpoa"> <name>Usage with SDP Offer/Answer Model</name> <t>This section describes the negotiation of unicast messages using theoffer/answerOffer/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 configuration apply:</t> <t>The parameters identifying a media format configuration for EVC are profile-id and level-id. Profile_idMUST<bcp14>MUST</bcp14> be used symmetrically.</t><t>The<!-- [rfced] The text introduces three options, but only two bullet points follow. Is an option missing, or should the text refer to "two options"? Original: The answerer MUST structure its answer according to one of the following three options: * maintain all configuration parameters with the values 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 * remove the media format (payload type) completely (when one or more of the parameter values are not supported). --> <t>The Answerer <bcp14>MUST</bcp14> structure its answer according to one of the following two options:</t> <ulempty="true"><li> <t><list style="symbols"> <t>maintainspacing="normal"> <li>maintain all configuration parameters with the values 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</t> </list></t> </li></ul> <ul empty="true"><li> <t><list style="symbols"> <t>removeor</li> <li>remove the media format (payload type) completely (when one or more of the parameter values are notsupported).</t> </list></t> </li></ul> <t>Informativesupported).</li> </ul> <aside><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 format config) below.</t>("<xref target="formatconfig" format="title"/>").</t></aside> <t>To simplify handling and matching of these configurations, the same RTP payload type number used in the offerSHOULD<bcp14>SHOULD</bcp14> also be used in the answer, as specified in <xreftarget="RFC3264"></xref>.</t>target="RFC3264"/>.</t> <t>The answerMUST NOT<bcp14>MUST NOT</bcp14> contain a payload type number used in the offer for the media subtype unless the configuration is the same as in the offer or the configuration in the answer only differs from that in the offer with a different value of level-id.</t><!-- Section 7.3.2.x --><sectionanchor="formatconfig"><name>Payloadanchor="formatconfig"> <name>Payload Format Configuration</name> <t>The following limitations and rules pertain to the configuration of the payload format buffer management.</t><t>The<ul spacing="normal"> <li><t>The parameters sprop-max-don-diff and sprop-depack-buf-bytes describe the properties of an RTP stream that theoffererOfferer or theanswererAnswerer is sending for the media format configuration. This differs from the normal usage of theoffer/answerOffer/Answer parameters; normally, such parameters declare the properties of the bitstream or RTP stream that theoffererOfferer or theanswererAnswerer is able to receive. When dealing with EVC, theoffererOfferer assumes that theanswererAnswerer will be able to receive media encoded using the configuration beingoffered.</t> <t>Informativeoffered.</t></li> </ul> <aside><t>Informative note: The above parameters apply for any RTP stream, 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 may have to be applied to another payload type when being sent, as they apply for theconfiguration.</t> <t>Whenconfiguration.</t></aside> <ul spacing="normal"> <li><t>When anoffererOfferer offers an interleaved stream, indicated by the presence of sprop-max-don-diff with a value larger than zero, theofferer MUSTOfferer <bcp14>MUST</bcp14> include the size of the de-packetization buffersprop-depack-buf-bytes.</t> <t>Tosprop-depack-buf-bytes.</t></li> <li><t>To enable theoffererOfferer andanswererAnswerer to inform each other about their capabilities for de-packetization buffering in receiving RTP streams, both parties areRECOMMENDED<bcp14>RECOMMENDED</bcp14> to includedepack-buf-cap.</t> <t>Thedepack-buf-cap.</t></li> <li><t>The parameterssprop-sps,sprop-sps or sprop-pps, when present (included in the"a=fmtp""a=fmtp" line of SDP or conveyed using the"fmtp""fmtp" source attribute, as specified inSection 6.3 of<xreftarget="RFC5576"></xref>),target="RFC5576" sectionFormat="of" section="6.3"/>), are used for out-of-band transport of the parameter sets (SPS or PPS, respectively). Theanswerer MAYAnswerer <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 theofferer-to-answererOfferer-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 differentbitstreams;bitstreams: one from theanswererAnswerer to theoffererOfferer, and the other in the opposite direction. In case some RTP packets are sent before the SDPoffer/answerOffer/Answer settles down, in-band parameter setsMUST<bcp14>MUST</bcp14> be used for those RTP stream parts sent before the SDPoffer/answer.</t> <t>TheOffer/Answer.</t></li> <li><t>The following rules apply to transport of parameter sets in theofferer-to-answererOfferer-to-Answerer direction.</t><t>An<ul spacing="normal"> <li><t>An offerMAY<bcp14>MAY</bcp14> includesprop-sps,sprop-sps and/or sprop-pps. If none of these parameters are present in the offer, then only in-band transport of parameter sets isused.</t> <t>Ifused.</t></li> <li><t>If the level to use in theofferer-to-answererOfferer-to-Answerer direction is equal to the default level in the offer, theanswerer MUSTAnswerer <bcp14>MUST</bcp14> be prepared to use the parameter sets included insprop-sps,sprop-sps and sprop-pps (either included in the"a=fmtp""a=fmtp" line of SDP or conveyed using the"fmtp""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, theanswerer MUSTAnswerer <bcp14>MUST</bcp14> ignore sprop-vps, sprop-sps, and sprop-pps (either included in the"a=fmtp""a=fmtp" line of SDP or conveyed using the"fmtp""fmtp" sourceattribute)attribute), and theofferer MUSTOfferer <bcp14>MUST</bcp14> transmit parameter setsin-band.</t> <t>Thein-band.</t></li> </ul></li> <li><t>The following rules apply to transport of parameter sets in theanswerer-to-offererAnswerer-to-Offerer direction.</t><t>An<ul spacing="normal"> <li><t>An answerMAY<bcp14>MAY</bcp14> includesprop-sps,sprop-sps and/or sprop-pps. If none of these parameters are present in the answer, then only in-band transport of parameter sets isused.</t> <t>The offerer MUSTused.</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""a=fmtp" line of SDP or conveyed using the"fmtp""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 RTPstreams.</t> <t>Whenstreams.</t></li> </ul></li> <li><t>When sprop-sps and/or sprop-pps are conveyed using the"fmtp""fmtp" source attribute, as specified inSection 6.3 of<xreftarget="RFC5576"></xref>,target="RFC5576" sectionFormat="of" section="6.3"/>, the receiver of the parametersMUST<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""fmtp" source attribute. Parameter sets associated with one source (given as part of the"fmtp""fmtp" source attribute)MUST<bcp14>MUST</bcp14> only be used to decode NAL units conveyed in RTP packets from the same source (given as part of the"fmtp""fmtp" source attribute). When this mechanism is in use, SSRC collision detection and resolutionMUST<bcp14>MUST</bcp14> be performed as specified in <xreftarget="RFC5576"></xref>.</t>target="RFC5576"/>.</t></li> </ul> <t><xref target="params-interpretation"/> lists the interpretation of all the parameters thatMAY<bcp14>MAY</bcp14> be used for the various combinations of offer, answer, and direction attributes.</t> <figureanchor="params-interpretation"><artwork><![CDATA[anchor="params-interpretation"> <name>Interpretation of Parameters for Various Combinations of Offers, Answers, and Direction Attributes</name> <artwork><![CDATA[ sendonly --+ recvonly --+ | sendrecv --+ | | | | | profile-id C C P level-id D D P toolset-id C C P max-recv-level-id R R - sprop-max-don-diff P - P sprop-depack-buf-bytes P - P depack-buf-cap R R - sprop-sei P - P sprop-sps P - P sprop-pps P - P Legend: C: configuration for sending and receiving bitstreams D: changeableconfiguration,configuration; same as C, except possible to answer with a different but consistent value (see the semantics of the level-id parameter on these parameters beingconsistent-basically,consistent -- basically, level down-grading is allowed) P: properties of the bitstream to be sent R: receiver capabilities -: notusable,usable; when present MUST beignored Interpretation of Parameters for Various Combinations of Offers, Answers, and Direction Attributes. ]]></artwork></figure>ignored]]></artwork> </figure> <t>Parameters used for declaring receiver capabilities are, in general, downgradable, i.e., they express the upper limit for asender'ssender's possible behavior. Thus, a senderMAY<bcp14>MAY</bcp14> select to set its encoder using only lower/lesser or equal values of these parameters.</t> <t>When asender'ssender'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 impossible to offer multiple configurations in a single payload type. Thus, when multiple configuration offers are made, each offer requires its own RTP payload type associated with the offer.</t> <t>An implementationSHOULD<bcp14>SHOULD</bcp14> be able to understand all media type parameters (including all optional media type parameters), even if itdoesn'tdoesn't support the functionality related to the parameter. This, in conjunction with proper application logic in the implementation, allows the implementation, after having received an offer, to create an answer by potentially downgrading one or more of the optional parameters to the point where the implementation cancope, leadingcope. This leads to higher chances of interoperability beyond the most basic interop points (for which, as described above, no optional parameters are necessary).</t><t>Informative<aside><t>Informative note: In implementations of various H.26x video coding payloadFormatsformats including those for <xref target="AVC"/> and <xref target="HEVC"/>, it was occasionally observed that implementations were incapable of parsing most (or all) of the optional parameters and hence rejected offers other than the most basic offers. As a result, theoffer/answerOffer/Answer exchange resulted in a baseline performance (using the default values for the optional parameters) with the resulting suboptimal user experience. However, there are valid reasons to forego the implementation complexity of implementing the parsing of some or all of the optional parameters, for example, when there is predetermined knowledge, not negotiated by an SDP-basedoffer/answerOffer/Answer process, of the capabilities of the involved systems (walled gardens, baseline requirements defined in application standards higher up in the stack, andsimilar).</t>similar).</t></aside> <t>Ananswerer MAYAnswerer <bcp14>MAY</bcp14> extend the offer with additional media format configurations. However, to enable their usage, in most cases, a second offer is required from theoffererOfferer to provide the bitstream property parameters that the media sender will use. This also has the effect that theoffererOfferer has to be able to receive this media format configuration, and not only to send it.</t> </section> </section> <sectionanchor="multicast"><name>Multicast</name>anchor="multicast"> <name>Multicast</name> <t>For bitstreams being delivered over multicast, the following rules apply:</t><t>The<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,MUST<bcp14>MUST</bcp14> be used symmetrically; that is, theanswerer MUSTAnswerer <bcp14>MUST</bcp14> either maintain all configuration parameters or remove the media format (payload type) completely. Note that this implies that the level-id foroffer/answerOffer/Answer in multicast is notchangeable.</t> <t>Tochangeable.</t></li> <li><t>To simplify the handling and matching of these configurations, the same RTP payload type number used in the offerSHOULD<bcp14>SHOULD</bcp14> also be used in the answer, as specified in <xreftarget="RFC3264"></xref>.target="RFC3264"/>. An answerMUST NOT<bcp14>MUST NOT</bcp14> contain a payload type number used in the offer unless the configuration is the same as in theoffer.</t> <t>Parameteroffer.</t></li> <li><t>Parameter sets receivedMUST<bcp14>MUST</bcp14> be associated with the originating source andMUST<bcp14>MUST</bcp14> only be used in decoding the incoming bitstream from the samesource.</t> <t>Thesource.</t></li> <li><t>The rules for other parameters are the same as above for unicast as long as the three above rules areobeyed.</t>obeyed.</t></li> </ul> </section> <sectionanchor="declativeSessiondesc"><name>Usageanchor="declativeSessiondesc"> <name>Usage in Declarative Session Descriptions</name> <t>When EVC over RTP is offered with SDP in a declarative style, as inReal Timethe Real-Time Streaming Protocol (RTSP) <xreftarget="RFC7826"></xref>target="RFC7826"/> or Session Announcement Protocol (SAP) <xreftarget="RFC2974"></xref>,target="RFC2974"/>, the following considerations apply.</t><t>All<ul spacing="normal"> <li><t>All parameters capable of indicating both bitstream properties 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 result, the following interpretation of the parametersMUST<bcp14>MUST</bcp14> be used:</t><t>Declaring<!-- [rfced] Note that we have updated the formatting of the following text to match what appears in RFC 9328 (see https://www.rfc-editor.org/rfc/rfc9328.html#section-7.3.4). Please let us know if any updates are needed. Original: Declaring actual configuration or bitstreamproperties:</t> <t>profile-idproperties: profile-id level-id sprop-sps sprop-pps sprop-max-don-diffsprop-depack-buf-bytes sprop-sei</t> <t>Notsprop- depack-buf-bytes sprop-sei Not usable (when present, they MUST be ignored): depack-buf-cap recv-sublayer-id --> <ul><li> <t>Declaring actual configuration or bitstream properties:</t> <ul spacing="compact"><li><t>profile-id</t></li> <li><t>level-id</t></li> <li><t>sprop-sps</t></li> <li><t>sprop-pps</t></li> <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><t>depack-buf-cap recv-sublayer-id</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 receiverMUST<bcp14>MUST</bcp14> reject (RTSP) or not participate in (SAP) the session. It falls on the creator of the session to use values that are expected to be supported by the receivingapplication.</t>application.</t></li> </ul> </li> </ul> </section> <sectionanchor="consider4pps"><name>Considerationsanchor="consider4pps"> <name>Considerations for Parameter Sets</name> <t>When out-of-band transport of parameter sets is used, parameter setsMAY<bcp14>MAY</bcp14> still be additionally transported in-band unless explicitly disallowed by an application, 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 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 the parameter set.</t> <!-- Section 8 --> </section> </section> </section> <sectionanchor="FeedbackMessage"><name>Useanchor="FeedbackMessage"> <name>Use with Feedback Messages</name><t>The<!-- [rfced] For simplicity, may we update these two sentences to the following sentence? Original: The following subsections define the use of the Picture Loss Indication (PLI) and Full Intra Request (FIR) feedback messages with<xref target="EVC"/>.[EVC]. The PLI is defined in<xref target="RFC4585"/>,[RFC4585], and the FIR message is defined in [RFC5104]. Perhaps: The following subsections define the use of the Picture Loss Indication (PLI) [RFC4585] and Full Intra Request (FIR) [RFC5104] feedback messages with [EVC]. --> <t>The following subsections define the use of the Picture Loss Indication (PLI) <xref target="RFC4585" format="default"/> and Full Intra Request (FIR) <xreftarget="RFC5104"/>.</t>target="RFC5104" format="default"/> feedback messages with <xref target="EVC"/>.</t> <t>In accordance with this document, a senderMUST NOT<bcp14>MUST NOT</bcp14> send Slice Loss Indication (SLI) or Reference Picture Selection Indication(RPSI),(RPSI); and a receiverMUST<bcp14>MUST</bcp14> ignore RPSI andMUST<bcp14>MUST</bcp14> treat a received SLI as a received PLI, ignoring the"First", "Number","First", "Number", and"PictureID""PictureID" fields of the PLI.</t><!-- Section 8.1 --><sectionanchor="PLI"><name>Pictureanchor="PLI"> <name>Picture Loss Indication (PLI)</name> <t>As specified inSection 6.3.1 of<xreftarget="RFC4585"/>,target="RFC4585" sectionFormat="of" section="6.3.1"/>, the reception of a PLI by a media sender indicates"the"the loss of an undefined amount of coded video data belonging to one or morepictures".pictures". Without having any specific knowledge of the setup of the bitstream (such as use and location of in-band parameter sets, IDR picture locations, picture structures, and so forth), a reaction to the reception of a PLI byaan EVC senderSHOULD<bcp14>SHOULD</bcp14> be to send an IDR picture and relevant parameter sets, potentially with sufficient redundancy so as to ensure correct reception. However, sometimes information about the bitstream structure is known. For example, such information can be parameter sets that have been conveyed out of band through mechanisms not defined in this document and that are known 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 examples could be devised based on a priori knowledge of different aspects of the bitstream structure. In all cases, the timing andcongestion controlcongestion-control mechanisms of <xref target="RFC4585"/>MUST<bcp14>MUST</bcp14> be observed.</t><!-- Section 8.2 --></section> <sectionanchor="FIR"><name>Fullanchor="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 senderMUST<bcp14>MUST</bcp14> send an IDR picture. Parameter setsMUST<bcp14>MUST</bcp14> 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, that parameter sets are exclusively sent out of band.</t> </section> </section> <sectionanchor="Security"><name>Securityanchor="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 risk if implemented naively. The payload format, in isolation, does not form a complete system. Implementers are advised to read and understand relevant security-related documents, especially those pertaining to RTP (see the Security Considerationssectionin <xreftarget="RFC3550"/>)target="RFC3550" sectionFormat="of" section="14"/>) 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 coding and decoding implementations in general and avoid 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-based 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 <xreftarget="RFC3550"/>,target="RFC3550"/> and in any applicable RTP profile such as RTP/AVP <xref target="RFC3551"/>, RTP/AVPF <xref target="RFC4585"/>, RTP/SAVP <xref target="RFC3711"/>, or RTP/SAVPF <xref target="RFC5124"/>. However, as"Securing the RTP Framework: Why RTP Does Not Mandate a Single Media Security Solution""<xref target="RFC7202" format="title"/>" <xreftarget="RFC7202"/>target="RFC7202" format="default"/> discusses, it is not an RTP payloadformat'sformat's responsibility to discuss or mandate what solutions are used to meet the basic security goals like confidentiality,integrityintegrity, and source authenticity for RTP in general. This responsibilitylayslies on anyone using RTP in an application. They can find guidance on available security mechanisms and important considerations in"Options for Securing RTP Sessions""<xref target="RFC7201" format="title"/>" <xreftarget="RFC7201"/>.target="RFC7201" format="default"/>. ApplicationsSHOULD<bcp14>SHOULD</bcp14> use one or more appropriate strong security mechanisms. The rest of this section discusses the security impacting properties of the payload format itself.</t> <t>Because the data compression used with this payload format is appliedend-to-end,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 have non-uniform receiver-end computational load. The attacker can inject pathological 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 integrity protection of at least the RTP packet isRECOMMENDED<bcp14>RECOMMENDED</bcp14> based onthe thoughts of<xref target="RFC7202"/>.</t> <t>Like HEVC <xref target="RFC7798"/> and VVC <xref target="VVC"/>, EVC <xref target="EVC"/> includes a user data Supplemental Enhancement Information (SEI) message. This SEI message allows inclusion of an arbitrary bitstring into the video bitstream. Such a bitstring could include JavaScript, machine code, and other active content.</t><t><xref target="EVC"></xref><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 message, decoder implementations cannot naively trust its content. For example, forwarding all received JavaScript code detected by a decoder implementation to aweb-browserweb 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 that 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 will 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 included in the security context establishment.</t> </section> <sectionanchor="CC"><name>Congestionanchor="CC"> <name>Congestion Control</name> <t>Congestion control for RTPSHALL<bcp14>SHALL</bcp14> 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 additional requirement is that users of this payload formatMUST<bcp14>MUST</bcp14> monitor packet loss to ensure that the packet loss rate is within an acceptable range. <!-- [rfced] May we remove "are achieved" from the end of the sentence? Otherwise, please clarify how it relates to the rest of the sentence? Current: Packet loss is considered acceptable if a TCP flow across the same network path and experiencing the same network conditions would achieve an average throughput, measured on a reasonable timescale, that is not less than all RTP streams combined are achieved. --> Packet loss is considered acceptable if a TCP flow across the same network path and experiencing the same network conditions would achieve an average throughput, measured on a reasonable timescale, that is not less than all RTP streams combined. This condition can be satisfied by implementing congestion-control mechanisms to adapt the transmissionrate,rate by implementing the number of layers subscribed for a layered multicastsession,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 adequately tuning the quantization parameter. However, when pre-encoded content is being transmitted, bandwidth adaptation requires the pre-coded bitstream to be tailored for such adaptivity.</t> <t>The key mechanism available in <xreftarget="EVC"></xref>target="EVC"/> is temporal scalability. A media sender can remove NAL units belonging to higher temporal sub-layers (i.e., those NAL units with a large value of TID) until the sending bitrate drops to an acceptable range.</t> <t>The mechanisms mentioned above generally work within a defined profile and level;thereforetherefore, no renegotiation of the channel is required. Only when non-downgradable parameters (such as the profile) are required to be changed does it become necessary to terminate and restart the RTPstream(s).streams. This may be accomplished by using different RTP payload types.</t> <t>MANEsMAY<bcp14>MAY</bcp14> remove certain unusable packets from the RTP stream when that RTP stream was damaged due to previous packet losses. This can help reduce the network load in certain special cases. For example, MANEs can remove those FUs where the leading FUs belonging to the same NAL unit have been lost, because the trailing FUs are meaningless to most decoders. MANE can also remove higher temporal scalable layers if the outbound transmission (from theMANE'sMANE's viewpoint) experiences congestion.</t> </section> <sectionanchor="iana-considerations"><name>IANAanchor="iana-considerations"> <name>IANA Considerations</name><t>A new<t>The mediatype, astype specified in <xref target="oparams"/>of this document,has been registered with IANA.</t> </section><section anchor="acknowledgements"><name>Acknowledgements</name> <t>Large parts of this specification share text with the RTP payload format for VVC <xref target="RFC9328"/>. Roman Chernyak is thanksed for his valueable review comments. We thank the authors of that specification for their excellent work.</t> </section></middle> <back><references title='Normative References'><references> <name>References</name> <references> <name>Normative References</name> <reference anchor="ISO23094-1" target="https://www.iso.org/standard/57797.html"> <front><title>ISO/IEC DIS Information<title>Information technology---- General video coding---- Part11: Essential video coding</title><author > <organization></organization><author> <organization/> </author> <dateyear="n.d."/>month="October" year="2020"/> </front> <seriesInfo name="ISO/IEC" value="23094-1:2020"/> </reference> <!-- [rfced] May we remove the reference to [ISO23094-1], as it appears to be a duplicate to [EVC]. Note that we will update the reference entry and use [EVC] as the citation tag (as [EVC] was used more frequently and aligns with similar reference tags). Original [EVC] "ISO/IEC 23094-1 Essential Video Coding", 2020, <https://www.iso.org/standard/57797.html>. [ISO23094-1] "ISO/IEC DIS Information technology - General video coding - Part 1 Essential video coding", n.d., <https://www.iso.org/standard/57797.html>. --> <reference anchor="EVC" target="https://www.iso.org/standard/57797.html"> <front><title>ISO/IEC 23094-1<title>Information technology -- General video coding -- Part 1: EssentialVideo Coding</title> <author > <organization></organization>video coding</title> <author> <organization/> </author> <date month="October" year="2020"/> </front> <seriesInfo name="ISO/IEC" value="23094-1:2020"/> </reference><reference anchor="RFC9328"> <front> <title>RTP Payload Format<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9328.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3550.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3551.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3711.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4585.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5124.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3264.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8866.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4648.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5576.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5104.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8082.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7826.xml"/> <!-- [VSEI] has been updated to point to the 2024 release. Please let us know if any corrections are needed. Original: [VSEI] "Versatile supplemental enhancement information messages forVersatile 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 formatcoded video bitstreams", 2020, <https://www.itu.int/rec/T-REC-H.274>. Current: [VSEI] ITU-T, "Versatile supplemental enhancement information messages forthe Versatile Video Coding (VVC) specification, which was published as bothcoded video bitstreams", ITU-T RecommendationH.266 and ISO/IEC International Standard 23090-3. VVC was developed by the Joint Video Experts Team (JVET). The RTP payload format allowsH.274, March 2024, <https://www.itu.int/rec/T-REC-H.274>. --> <reference anchor="VSEI" target="https://www.itu.int/rec/T-REC-H.274"> <front> <title>Versatile supplemental enhancement information messages forpacketization of one or more 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 wide applicability in videoconferencing, Internetcoded videostreaming, and high-bitrate entertainment-quality video, among other applications.</t> </abstract>bitstreams</title> <author> <organization>ITU-T</organization> </author> <date month="March" year="2024"/> </front> <seriesInfoname="RFC" value="9328"/> <seriesInfo name="DOI" value="10.17487/RFC9328"/>name="ITU-T Recommendation" value="H.274"/> </reference> </references> <references> <name>Informative References</name> <referenceanchor="RFC2119">anchor="MPEG2S"> <front><title>Key words for use in RFCs to Indicate Requirement Levels</title> <author fullname="S. Bradner" initials="S." surname="Bradner"/><title>Information technology - Generic coding of moving pictures and associated audio information - Part 1: Systems</title> <author> <organization>IS0/IEC</organization> </author> <datemonth="March" year="1997"/> <abstract> <t>In many standards track documents several words are usedmonth="June" year="2013"/> </front> <seriesInfo name="ISO/IEC" value="13818-1:2013"/> </reference> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6184.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6190.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7656.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7667.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7201.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7202.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7798.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2974.xml"/> <!-- [rfced] We have updated [HEVC] to point tosignifytherequirementsmost recent version published inthe specification. These words2023. Please let us know if any corrections areoften capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t> </abstract>needed. Original: [HEVC] "High efficiency video coding, ITU-T Recommendation H.265", 2019, <https://www.itu.int/rec/T-REC-H.265>. Current: [HEVC] ITU-T, "High efficiency video coding", ITU-T Recommendation H.265, September 2023, <https://www.itu.int/rec/T-REC-H.265>. --> <reference anchor="HEVC" target="https://www.itu.int/rec/T-REC-H.265"> <front> <title>High efficiency video coding</title> <author> <organization>ITU-T</organization> </author> <date month="" year="2019"/> </front> <seriesInfoname="BCP" value="14"/> <seriesInfo name="RFC" value="2119"/> <seriesInfo name="DOI" value="10.17487/RFC2119"/>name="ITU-T Recommendation" value="H.265"/> </reference> <referenceanchor="RFC3550">anchor="VIDEO-CODING" target="https://www.itu.int/rec/T-REC-H.263"> <front><title>RTP: A Transport Protocol<title>Video coding forReal-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"/>low bit rate communication</title> <author> <organization>ITU-T</organization> </author> <datemonth="July" year="2003"/> <abstract> <t>This memorandum describes RTP, the real-time transport protocol. RTP provides end-to-end network transport functions suitable for applications transmitting 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 transportmonth="January" year="2005"/> </front> <seriesInfo name="ITU-T Recommendation" value="H.263"/> </reference> <!-- [rfced] For reference [AVC], isaugmented by a control protocol (RTCP) to allow monitoring ofthedata delivery in a manner scalable to large multicast networks, and to provide minimal control and identification functionality. RTP and RTCP are designedintended reference tobe independent of the underlying transport and network layers. The protocol supports the use of RTP-level translators and mixers. Most of the text in this memorandumH.264 <https://www.itu.int/rec/T-REC-H.264>? If not, isidentical to RFC 1889 which it obsoletes. There are no changes in the packet formats on the wire, only changes totherules and algorithms governing how the protocol is used. The biggest change is an enhancementintent to reference ISO/IEC 14496-10:2022 <https://www.iso.org/standard/83529.html>? Note that on thescalable timer algorithm for calculating when to send RTCP packets in order to minimize transmission in excesslanding page of theintended rate when many participants join a session simultaneously. [STANDARDS-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</title> <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 ofprovided iso.org URL, thereal-time transport protocol (RTP), version 2,title does not match and theassociated control protocol, RTCP, within audio andstatus is "Withdrawn". Original: [AVC] "ITU-T Recommendation H.264 - Advanced videomultiparticipant conferences with minimal control. It provides interpretations of generic fields within the RTP specification suitablecoding foraudio and video conferences. In particular, this document defines a setgeneric audiovisual services", 2014, <https://www.iso.org/standard/66069.html>. Perhaps A: [AVC] ISO/IEC, "Information technology Coding ofdefault mappings from payload type numbers to encodings. This document also describes how audio andaudio-visual objects Part 10: Advanced Video Coding", ISO/IEC 14496-10:2014, September 2019, <https://www.iso.org/standard/66069.html>. Perhaps B: [AVC] ITU-T, "Advanced videodata may be carried within RTP. It defines a set of standard encodings and their names when used within RTP. The descriptions provide pointers to reference implementations and the detailed standards. This document is meant as an aidcoding forimplementors of audio,generic audiovisual services", ITU-T Recommendation H.264, February 2014, <https://www.itu.int/rec/T-REC-H.264>. --> <reference anchor="AVC" target="https://www.iso.org/standard/66069.html"> <front> <title>Part 10: Advanced videoand other real-time multimedia applications. This memorandum obsoletes RFC 1890. It is mostly backwards-compatible except for functions removed because two interoperable implementations were not found. The additions to RFC 1890 codify existing practice in the use of payload formats under this profile and include new payload formats defined since RFC 1890 was published. [STANDARDS-TRACK]</t> </abstract>coding</title> <author> <organization>ITU-T</organization> </author> <date month="October" year="2014"/> </front> <seriesInfoname="STD" value="65"/> <seriesInfo name="RFC" value="3551"/> <seriesInfo name="DOI" value="10.17487/RFC3551"/>name="ITU-T Recommendation" value="H.264"/> </reference> <referenceanchor="RFC3711">anchor="VVC" target="http://www.itu.int/rec/T-REC-H.266"> <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"/><title>Versatile video coding</title> <author> <organization>ITU-T</organization> </author> <datemonth="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 confidentiality, 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>month="August" year="2020"/> </front> <seriesInfoname="RFC" value="3711"/> <seriesInfo name="DOI" value="10.17487/RFC3711"/>name="ITU-T Recommendation" value="H.266"/> </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 against packet losses. Receivers may use the base mechanisms</references> </references> <section anchor="acknowledgements" numbered="false" toc="default"> <name>Acknowledgements</name> <t>Large parts of this specification share text with theReal-time Transport Control Protocol (RTCP) to report packet reception statistics and thus allow a sender to adapt its transmission behavior in the mid-term. ThisRTP payload format for VVC <xref target="RFC9328"/>. <contact fullname="Roman Chernyak"/> isthe sole meansthanked forfeedback and feedback-based error repair (besides a few codec-specific mechanisms). This document defines an extension tohis valuable review comments. We thank theAudio-visual Profile (AVP)authors of thatenables receivers to provide, statistically, more immediate feedback to the senders and thus allowsspecification forshort-term adaptation and efficient feedback-based repair mechanismstheir excellent work.</t> </section> <!-- [rfced] The following sentences or phrases seem tobe implemented. This early feedback profile (AVPF) maintainsintroduce a list of items. Please consider whether theAVP bandwidth constraints for RTCP and preserves scalability to large groups. [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 profile (AVPF) to provide timely feedbackreader would benefit fromthe receiversformatting toa senderhelp clarify which paragraphs aredefinedincluded in "the following." We note that RFC3711 and RFC 4585, respectively. This memo specifies9328 uses lists for these as well. A) Section 7.3.2.1 - do you want thecombination of both profilestext toenable secure RTP communications with feedback. [STANDARDS-TRACK]</t> </abstract> </front> <seriesInfo name="RFC" value="5124"/> <seriesInfo name="DOI" value="10.17487/RFC5124"/> </reference> <reference anchor="RFC8174"> <front> <title>Ambiguity of Uppercase vs Lowercaseappear inRFC 2119 Key Words</title> <author fullname="B. Leiba" initials="B." surname="Leiba"/> <date month="May" year="2017"/> <abstract> <t>RFC 2119 specifies common key words that may be usedlist form as it is inprotocol specifications. This document aimsRFC 9328? Original: The following limitations and rules pertain toreducetheambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.</t> </abstract> </front> <seriesInfo name="BCP" value="14"/> <seriesInfo name="RFC" value="8174"/> <seriesInfo name="DOI" value="10.17487/RFC8174"/> </reference> <reference anchor="RFC3264"> <front> <title>An Offer/Answer Model with Session Description Protocol (SDP)</title> <author fullname="J. Rosenberg" initials="J." surname="Rosenberg"/> <author fullname="H. Schulzrinne" initials="H." surname="Schulzrinne"/> <date month="June" year="2002"/> <abstract> <t>This document defines a mechanism by which two entities can make useconfiguration of theSession Description Protocol (SDP)payload format buffer management. The following rules apply toarrive at a common viewtransport ofa multimedia session between them. In the model, one participant offersparameter sets in theother a descriptionofferer-to-answerer direction. The following rules apply to transport of parameter sets in thedesired session from their perspective,answerer-to-offerer direction. Section 7.3.2: Original: The following limitations and rules pertaining to theother participant answers withmedia configuration apply: Section 7.3.3: Original: For bitstreams being delivered over multicast, thedesired session from their perspective. This offer/answer model is most useful in unicast sessions where information from both participants is needed forfollowing rules apply: Section 7.3.4: as noted above, we updated thecomplete viewformat ofthe session. The offer/answer model is used by protocolsthis section for clarity. We would like confirmation that matching theSession Initiation Protocol (SIP). [STANDARDS-TRACK]</t> </abstract> </front> <seriesInfo name="RFC" value="3264"/> <seriesInfo name="DOI" value="10.17487/RFC3264"/> </reference> <reference anchor="RFC8866"> <front> <title>SDP: Session Description Protocol</title> <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). SDPformat of 9328 is intendedfor describing multimedia sessions for the purposes of session announcement, session invitation, and other forms of multimedia session initiation. This document obsoletes RFC 4566.</t> </abstract> </front> <seriesInfo name="RFC" value="8866"/> <seriesInfo name="DOI" value="10.17487/RFC8866"/> </reference> <reference anchor="RFC4648"> <front> <title>The Base16, Base32, and Base64 Data Encodings</title> <author fullname="S. Josefsson" initials="S." surname="Josefsson"/> <date month="October" year="2006"/> <abstract> <t>This document describesbefore making further updates. --> <!-- [rfced] We have a few specific questions about abbreviations: A) For thecommonly used base 64, base 32, and base 16 encoding schemes. It also discussesabbreviation "RGB", theuse of line-feeds in encoded data, use of padding in encoded data, use of non-alphabet characters in encoded data, use of different encoding alphabets, and canonical encodings. [STANDARDS-TRACK]</t> </abstract> </front> <seriesInfo name="RFC" value="4648"/> <seriesInfo name="DOI" value="10.17487/RFC4648"/> </reference> <reference anchor="RFC5576"> <front> <title>Source-Specific Media Attributes in the Session Description Protocol (SDP)</title> <author fullname="J. Lennox" initials="J." surname="Lennox"/> <author fullname="J. Ott" initials="J." surname="Ott"/> <author fullname="T. Schierl" initials="T." surname="Schierl"/> <date month="June" year="2009"/> <abstract> <t>The Session Description Protocol (SDP) provides mechanisms to describe attributes of multimedia sessions and of individual media streams (e.g., Real-time Transport Protocol (RTP) sessions) within a multimedia session,definition is "Same as GBR", butdoes"GBR" is notprovide any mechanism to describe individual media sources within a media stream. This document defines a mechanism to describe RTP media sources, which are identified by their synchronization source (SSRC) identifiers, in SDP, to associate attributes with these sources, and to express relationships among sources. It also defines several source-level attributes that can be used to describe properties of media sources. [STANDARDS-TRACK]</t> </abstract> </front> <seriesInfo name="RFC" value="5576"/> <seriesInfo name="DOI" value="10.17487/RFC5576"/> </reference> <reference anchor="RFC5104"> <front> <title>Codec Control Messages in the RTP Audio-Visual Profile with Feedback (AVPF)</title> <author fullname="S. Wenger" initials="S." surname="Wenger"/> <author fullname="U. Chandra" initials="U." surname="Chandra"/> <author fullname="M. Westerlund" initials="M." surname="Westerlund"/> <author fullname="B. Burman" initials="B." surname="Burman"/> <date month="February" year="2008"/> <abstract> <t>This document specifies a few extensions to the messagesdefined in theAudio-Visual Profile with Feedback (AVPF). They are helpful primarily in conversational multimedia scenarios where centralized multipoint functionalities are in use. However, somedocument. How may we update this definition term/expansion? Original: RGB: Same as GBR B) The following abbreviations arealso usablenot expanded insmaller multicast environments and point-to-point calls.</t> <t>The extensions discussed are messages related totheITU-T Rec. H.271 Video 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"> <front> <title>Using Codec Control Messages intext. May we expand theRTP Audio-Visual Profile with Feedback with Layered Codecs</title> <author fullname="S. Wenger" initials="S." surname="Wenger"/> <author fullname="J. Lennox" initials="J." surname="Lennox"/> <author fullname="B. Burman" initials="B." surname="Burman"/> <author fullname="M. Westerlund" initials="M." surname="Westerlund"/> <date month="March" year="2017"/> <abstract> <t>This document updates RFC 5104 by fixing a shortcomingterms as follows? Please consider whether these should appear inthe specification 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 onanylayerof thelayered bitstream, regardless of whether those layers are being sent in a single or in multiple RTP flows. The other payload-specific feedback messages defined in RFC 5104 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"> <front> <title>Real-Time Streaming Protocol Version 2.0</title> <author fullname="H. Schulzrinne" initials="H." surname="Schulzrinne"/> <author fullname="A. Rao" initials="A." surname="Rao"/> <author fullname="R. Lanphier" initials="R." surname="Lanphier"/> <author fullname="M. Westerlund" initials="M." surname="Westerlund"/> <author fullname="M. Stiemerling" initials="M." role="editor" surname="Stiemerling"/> <date month="December" year="2016"/> <abstract> <t>This memorandum defines the Real-Time Streaming Protocol (RTSP) version 2.0, which obsoletes RTSP version 1.0 definedabbreviations sections. CABAC - as expanded in RFC2326.</t> <t>RTSP is an application-layer protocol for the setup and control of9328: context adaptive binary arithmetic coding [CABAC] Where thedelivery of data with real-time properties. RTSP provides an extensible framework 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 protocolreference entry isintended to control multiple data delivery sessions; provide a means for choosing delivery channels suchasUDP, 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"> <front> <title>Versatile supplemental enhancement information messages for coded video bitstreams</title> <author > <organization></organization> </author> <date year="2020"/> </front> </reference> </references> <references title='Informative References'> <reference anchor="MPEG2S" > <front> <title>Information technology - Genericfollows: [CABAC] Sole, J., et al., "Transform coefficient codingofmoving picturesin HEVC", IEEE Transactions on Circuits andassociated audio information - Part 1:Systems, ISO International Standard 13818-1</title> <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 formatSystems forthe ITU-T Recommendation H.264 video codec and the technically identical ISO/IEC International Standard 14496-10 video codec, excluding the ScalableVideoCoding (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 moreTechnology, DOI 10.1109/TCSVT.2012.2223055, December 2012, <https://doi.org/10.1109/TCSVT.2012.2223055>. CRA - clean random access (CRA) DON - Decoding Order Number MCU - Multipoint Control Units (MCUs) NALU - Network Abstraction LayerUnits (NALUs), produced by an H.264 video encoder, in each RTP payload. The payload format has wide applicability, as it supports applications from simple low bitrate conversational usage, to Internet video streaming with interleaved transmission, to high bitrate video-on-demand.</t> <t>This memo obsoletes RFC 3984. Changes from RFC 3984 are summarizedUnit SD TV - standard-definition television C) ADDB is introduced, but it's not used elsewhere inSection 14. Issues on backward compatibilitythe document. Do you want toRFC 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 describesinclude the abbreviated form or should "(ADDB)" be removed? Original: In the Main profile, anRTP payload format for Scalable Video Coding (SVC)Advanced Deblocking Filter (ADDB) can be used asdefined in Annex G of ITU-T Recommendation H.264,an alternative, whichis technically identical to Amendment 3 of ISO/IEC International Standard 14496-10. The RTP payload format allows for packetization of one or more Network Abstraction Layer (NAL) units in each RTP packet payload, as well as fragmentation ofcan further reduce undesirable compression artifacts. --> <!-- [rfced] We have aNAL unitfew specific questions about terminology related to hyphens, slashes, and capitalization: A) To match usage inmultiple 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 compatibleRFCs 7798 and 9328, may we update the terms toRFC 6184 sincethebase layer, when encapsulated in its own RTP stream, must useform on theH.264 media subtype name ("H264") andright? Inter-prediction > Inter prediction intra-coding > intra coding offer/answer > Offer/Answer answerer > Answerer offerer > Offerer B) Please review thepacketization method specified in RFC 6184. The payload format has wide applicability in videoconferencing, Internet video streaming, 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 Taxonomyusage ofSemantics and Mechanisms for Real-Time Transport Protocol (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,the slashes (/) in the following terms andassociations among, Real-time Transport Protocol (RTP) sourceslet us know if they can becomplex and somewhat opaque. This document describes a numberreplaced with "and", "or", or "and/or" for clarity. mapping/clipping function transmissions/updates --> <!-- [rfced] We have some general questions about certain terms: A) We see instances ofexistingboth "Start bit" andproposed properties"End bit" used in the following, but "S bit" andrelationships among RTP sources"E bit" used elsewhere. Please let us know if S bit anddefines common terminologyE bit should be used here fordiscussing protocol entitiesconsistency. Should Start bit andtheir relationships.</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-pointEnd bit be introduced where S bit andmulti-endpoint topologies used in environments based on the Real-time Transport Protocol (RTP). In particular, centralized topologies commonly employed in the video conferencing industryE bit aremapped 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 usedfirst introduced? Original: A non-fragmented NAL unit MUST NOT be transmitted ina large number of different application domainsone FU; i.e., the Start bit andenvironments. This heterogeneity implies that different security mechanisms are neededEnd bit MUST NOT both be set toprovide services such as confidentiality, integrity, and source authentication of RTP and RTP Control Protocol (RTCP) packets suitable for1 in thevarious environments.same FU header. B) Therange of solutions makes it difficult for RTP-based application developers to pickfollowing levels are named in themost suitable mechanism. This document provides an overview oftext. Do they all require anumber of security solutions for RTP and gives guidance for developers on how to choosedecimal, or may we remove theappropriate security mechanism.</t> </abstract> </front> <seriesInfo name="RFC" value="7201"/> <seriesInfo name="DOI" value="10.17487/RFC7201"/> </reference> <reference anchor="RFC7202"> <front> <title>Securingdecimal from 3.0 (3.0 > 3) to make it consistent with theRTP Framework: Why RTP Does Not Mandate a Single Media Security 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 discussesothers? level 1 level 2 level 3 level 3.0 --> <!-- [rfced] Please review theproblem"Inclusive Language" portion ofsecuring real-time multimedia sessions. It also explains whytheReal-time Transport Protocol (RTP) and the associated 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 mechanismsonline Style Guide <https://www.rfc-editor.org/styleguide/part2/#inclusive_language> and let us know if any changes aremandated andneeded. Note that our script did not flag anysuch mechanisms are specifiedwords in particular, but this should still be reviewed as amanner 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 formatbest practice. In addition, please consider whether "tradition" should be updated for clarity. While thevideo coding standard ITU-T Recommendation H.265 and ISO/IEC International Standard 23008-2, bothNIST website <https://www.nist.gov/nist-research-library/nist-technical-series-publications-author-instructions#table1> indicates that this term is potentially biased, it is alsoknownambiguous. "Tradition" is a subjective term, asHigh Efficiency Video Coding (HEVC) and developed byit is not theJoint Collaborative Team on Video Coding (JCT-VC). The RTP payload format allowssame forpacketization of one or more Network Abstraction Layer (NAL) units in each RTP packet payload as well as fragmentation ofeveryone. A) "traditional" EVC uses aNAL unittraditional block-based coding structure, which divides the encoded image intomultiple RTP packets. Furthermore, 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 applicability in videoconferencing, Internet video streaming, and high-bitrate entertainment-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 2blocks of up to 64x64 luma samples for themulticast session directory announcement protocol, Session Announcement Protocol (SAP),Baseline profile and 128x128 luma samples for therelated issues affecting security and scalabilityMain profile thatshouldcan betakenrecursively divided intoaccount by implementors. This memo defines an Experimental Protocol forsmaller blocks. B) "traditional" The Main profile adds two advanced coding structure tools: 1) Binary Ternary Tree (BTT) partitioning that allows non-square coding units and 2) Split Unit Coding Order segmentation that changes theInternet 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 - Advancedprocessing 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. C) "traditional" EVC also uses a traditional videocoding for generic audiovisual 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> <!-- ##markdown-source: H4sIAOeOgmUAA+2963IbR7Yu+B9PUSNFnCamAVqkJEqi246mSKrFM7pwE5T6 9PR2OApAgawWUIVdVSBFy97RP+f3xPw85zXmAeZR+klmXTNXZhVIyJb7MnPY bpsEqvK6cl2/tXI4HPaavJln+8nZ+Wlymt7My3SavCirRdoks7JKjus6K5o8 nSfv82lWJoflNC8ukq3j94f9XjoeV9kVv7uUd2fm3feHvWk5KdIFtD+t0lkz zLNmNkyvmklZZcOqWQ6zq8nwwZPeNG3gmd0Huw+HO7vDnWe9Xt2kxfT7dF4W 8EVTrTL8qMrSxX5ycnz+Iun18mVF39TN7oMHzx7s9lL4ej85ODvvXV/sJ9JL 78M1vFE0WVVkzfAIR9GbpM1+UjfTXm9C04GH60me95b5fvLnppwMkrqsoLNZ Db/dLPCX73q9dNVcltV+L6Gfofw3SfKi3k9G28n/fpmW7kOe9OhylebhF2V1 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h8MEwTe9/xdbgc2ffnkBAA==codecs prediction model assuming two general types of predictions: Intra (spatial) and Inter (temporal) predictions. --> </back> </rfc>