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RTP Payload Format for Essential Video Coding (EVC)
draft-ietf-avtcore-rtp-evc-07

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 9584.
Authors Shuai Zhao , Stephan Wenger , Youngkwon Lim
Last updated 2024-06-11 (Latest revision 2023-12-20)
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Formats
Reviews
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Dr. Bernard D. Aboba
Shepherd write-up Show Last changed 2023-07-30
IESG IESG state Became RFC 9584 (Proposed Standard)
Action Holders
(None)
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Murray Kucherawy
Send notices to bernard.aboba@gmail.com
IANA IANA review state Version Changed - Review Needed
IANA action state RFC-Ed-Ack
draft-ietf-avtcore-rtp-evc-07
avtcore                                                          S. Zhao
Internet-Draft                                                     Intel
Intended status: Standards Track                               S. Wenger
Expires: 21 June 2024                                            Tencent
                                                                  Y. Lim
                                                     Samsung Electronics
                                                        19 December 2023

          RTP Payload Format for Essential Video Coding (EVC)
                     draft-ietf-avtcore-rtp-evc-07

Abstract

   This document describes an RTP payload format for the Essential Video
   Coding (EVC) standard, published as ISO/IEC International Standard
   23094-1.  EVC was developed by the Moving Picture Experts Group
   (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.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 21 June 2024.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Overview of the EVC Codec . . . . . . . . . . . . . . . .   3
       1.1.1.  Coding-Tool Features (informative)  . . . . . . . . .   4
       1.1.2.  Systems and Transport Interfaces  . . . . . . . . . .   6
       1.1.3.  Parallel Processing Support (informative) . . . . . .   9
       1.1.4.  NAL Unit Header . . . . . . . . . . . . . . . . . . .   9
     1.2.  Overview of the Payload Format  . . . . . . . . . . . . .  10
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .  11
   3.  Definitions and Abbreviations . . . . . . . . . . . . . . . .  11
     3.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .  11
       3.1.1.  Definitions from the EVC Standard . . . . . . . . . .  11
       3.1.2.  Definitions Specific to This Document . . . . . . . .  13
     3.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .  14
   4.  RTP Payload Format  . . . . . . . . . . . . . . . . . . . . .  16
     4.1.  RTP Header Usage  . . . . . . . . . . . . . . . . . . . .  16
     4.2.  Payload Header Usage  . . . . . . . . . . . . . . . . . .  17
     4.3.  Payload Structures  . . . . . . . . . . . . . . . . . . .  17
       4.3.1.  Single NAL Unit Packets . . . . . . . . . . . . . . .  18
       4.3.2.  Aggregation Packets (APs) . . . . . . . . . . . . . .  19
       4.3.3.  Fragmentation Units . . . . . . . . . . . . . . . . .  23
     4.4.  Decoding Order Number . . . . . . . . . . . . . . . . . .  26
   5.  Packetization Rules . . . . . . . . . . . . . . . . . . . . .  27
   6.  De-packetization Process  . . . . . . . . . . . . . . . . . .  28
   7.  Payload Format Parameters . . . . . . . . . . . . . . . . . .  30
     7.1.  Media Type Registration . . . . . . . . . . . . . . . . .  30
     7.2.  Optional Parameters Definition  . . . . . . . . . . . . .  31
     7.3.  SDP Parameters  . . . . . . . . . . . . . . . . . . . . .  35
       7.3.1.  Mapping of Payload Type Parameters to SDP . . . . . .  35
       7.3.2.  Usage with SDP Offer/Answer Model . . . . . . . . . .  37
       7.3.3.  Multicast . . . . . . . . . . . . . . . . . . . . . .  41
       7.3.4.  Usage in Declarative Session Descriptions . . . . . .  42
       7.3.5.  Considerations for Parameter Sets . . . . . . . . . .  43
   8.  Use with Feedback Messages  . . . . . . . . . . . . . . . . .  43
     8.1.  Picture Loss Indication (PLI) . . . . . . . . . . . . . .  43
     8.2.  Full Intra Request (FIR)  . . . . . . . . . . . . . . . .  44
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  44
   10. Congestion Control  . . . . . . . . . . . . . . . . . . . . .  46

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   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  47
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  47
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  47
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  47
     13.2.  Informative References . . . . . . . . . . . . . . . . .  49
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  50

1.  Introduction

   The Essential Video Coding [EVC] standard, which is formally
   designated as ISO/IEC International Standard 23094-1 [ISO23094-1] has
   been published in 2020.  One goal of MPEG is to keep [EVC]'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] are reported
   to provide coding efficiency gains over High Efficiency Video Coding
   [HEVC] and Advanced Video Coding [AVC] under certain configurations.

   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 [RFC6184], Scalable Video Coding (SVC) [RFC6190], High
   Efficiency Video Coding (HEVC) [RFC7798], and Versatile Video Coding
   (VVC)[RFC9328].  With respect to design philosophy, security,
   congestion control, and overall implementation complexity, it has
   similar properties to those earlier payload format specifications.
   This is a conscious choice, as at least [RFC6184] is widely deployed
   and generally known in the relevant implementer communities.  Certain
   mechanisms known from [RFC6190] were incorporated as EVC supports
   temporal scalability.  EVC currently does not offer higher forms of
   scalability.

1.1.  Overview of the EVC Codec

   [EVC], [AVC], [HEVC] and [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 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 certain walled-garden implementations under
   commercial constraints imposed by intellectual property rights by
   including syntax elements that allow encoders to mark a bitstream as

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   to what of the many independent coding tools are exercised in the
   bitstream, in a spirit similar to the general_constraint_flags of
   [VVC].

   Conceptually, all EVC, AVC, HEVC and VVC include a Video Coding Layer
   (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.

1.1.1.  Coding-Tool Features (informative)

   Coding blocks and transform structure

   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.  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.  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 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.

   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
   different mapping/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 straightforward run-length
   encoding (RLE) based approach to encode the quantized coefficients.

   Entropy coding

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

   In-loop filtering

   The Baseline profile of EVC uses the deblocking filter defined in
   H.263 Annex J.  In the Main profile, an Advanced Deblocking Filter
   (ADDB) can be used as an alternative, which can further reduce
   undesirable compression artifacts.  The Main profile also defines two
   additional in-loop filters that can be used to improve the quality of
   decoded pictures before output and/or for 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.  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.  Similarly to VVC, the
   filter parameters of ALF are signaled in the Adaptation Parameter Set
   (APS).

   Inter-prediction

   The basis of EVC'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 a skip mode.  The
   Main profile includes six additional tools to provide improved inter-
   prediction.  With Advanced Motion Vectors Prediction (ADMVP),
   adjacent blocks can be conceptually merged to 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

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   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 additional
   signaling.

   Intra prediction and intra-coding

   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 the so-called Enhanced Intra
   Prediction Directions (EIPD).  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 this mode.

   Reference frames management

   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 the SPS.  For the Main profile, DPB management can be
   handled much more flexibly using explicitly signaled reference
   Picture Lists (RPL) in the SPS or slice level.

1.1.2.  Systems and Transport Interfaces

   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),
   two picture-level parameter sets (PPS and APS, each of which can
   apply to one or more pictures), slice-level header parameters, and
   lower-level parameters.

   A number of key components that influenced the Network Abstraction
   Layer design of EVC as well as this document, are described below:

   Sequence parameter set

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      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 generally started 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 switching MCUs involved), a CVS can be as
      long in duration as the whole session.

   Picture and adaptation parameter set

      The Picture Parameter Set and the Adaptation Parameter Set (PPS
      and APS, respectively) 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
      certain type whereas the APS contains information, such as
      adaptive loop filter coefficients, that are likely to change from
      picture to picture.

   Profile, level, and toolsets

      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 to confuse with the "toolset"
      discussed below) that a decoder compliant with this profile has to
      support.  In EVC, profiles are defined in Annex A.  Formally, they
      are defined as a set of constraints that a bitstream needs to
      conform to.  In EVC, the Baseline profile is much more severely
      constraint 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.

   Profiles and levels are signaled in the highest parameter set
   available, the SPS.

      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.  No decoder conformance point is associated with the
      toolset, but a bitstream that was using a coding tool that is

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      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.

   Bitstream and elementary stream

      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 not relevant.

   Random access support

      EVC supports random access mechanisms based on IDR and CRA access
      units.

   Temporal scalability support

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

   Reference picture management

      EVC's reference picture management is POC-based (Picture Order
      Count), similar to HEVC.  In the Main profile, substantially all
      reference picture list manipulations available in HEVC are
      available, including explicit transmissions/updates of reference
      picture lists, 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 structures only.

   SEI Message

      EVC inherits many of HEVC's SEI Messages, occasionally with syntax
      and/or semantics changes, making them applicable to EVC.  In
      addition, some of the codec-agnostic SEI Messages of the VSEI
      specification are also mapped.

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1.1.3.  Parallel Processing Support (informative)

      EVC's Baseline profile includes no tools specifically addressing
      parallel processing support.  The Main profile includes
      independently decodable slices for parallel processing.  The
      slices are defined as any rectangular region within a picture and
      can be encoded to have no coding dependencies with other slices in
      the same picture but with other slices from the previous picture.
      No specific support for parallel processing is specified in this
      RTP payload format.

1.1.4.  NAL Unit Header

   EVC maintains the NAL unit concept of [VVC] with different parameter
   options.  EVC also uses a two-byte NAL unit header, as shown in
   Figure 1.  The payload of a NAL unit refers to the NAL unit excluding
   the NAL unit header.

                        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

                                  Figure 1

   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.

   F: 1 bit

      forbidden_zero_bit.  Required to be zero in EVC.  Note that the
      inclusion of this bit in the NAL unit header was included to
      enable transport of EVC video over MPEG-2 transport systems
      (avoidance of start code emulations) [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
      Section 4.3.3.

   Type: 6 bits

      nal_unit_type_plus1.  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:

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      NalUnitType = nal_unit_type_plus1 - 1.

      The NAL unit type is detailed in Table 4 of [EVC].  If the value
      of NalUnitType is less than or equal to 23, the NAL unit is a VCL
      NAL unit.  Otherwise, the NAL unit is a non-VCL NAL unit.  For a
      reference of all currently defined NAL unit types and their
      semantics, please refer to Section 7.4.2.2 in [EVC].  Note that
      nal_unit_type_plus1 MUST NOT be zero.

   TID: 3 bits

      nuh_temporal_id.  This field specifies the temporal identifier of
      the NAL unit.  The value of TemporalId is equal to TID.
      TemporalId shall be equal to 0 if it is an IDR NAL unit type (NAL
      unit type 1).

   Reserve: 5 bits

      nuh_reserved_zero_5bits.  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 [EVC]'s Annex A shall ignore
      (i.e., remove from the bitstream and discard) all NAL units with
      values of nuh_reserved_zero_5bits greater than 0.

   E: 1 bit

      nuh_extension_flag.  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 [EVC]'s Annex A shall ignore (i.e., remove
      from the bitstream and discard) all NAL units with values of
      nuh_extension_flag equal to 1.

1.2.  Overview of the Payload Format

   This payload format defines the following processes required for
   transport of EVC-coded data over RTP [RFC3550]:

   *  usage of RTP header with this payload format

   *  packetization of EVC-coded NAL units into RTP packets using three
      types of payload structures: a single NAL unit, aggregation, and
      fragment unit

   *  transmission of EVC NAL units of the same bitstream within a
      single RTP stream.

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   *  media type parameters to be used with the Session Description
      Protocol (SDP) [RFC8866]

   *  usage of RTCP feedback messages

2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown above.

3.  Definitions and Abbreviations

3.1.  Definitions

   This document uses the terms and definitions of EVC.  Section 3.1.1
   lists relevant definitions from [EVC] for convenience.  Section 3.1.2
   provides definitions specific to this document.

3.1.1.  Definitions from the EVC Standard

   Access Unit: A set of NAL units that are associated with each other
   according to a specified classification rule, are consecutive in
   decoding order, and contain exactly one coded picture.

   Adaptation parameter set (APS): A syntax structure containing syntax
   elements that apply to zero or more slices as determined by zero or
   more syntax elements found in slice headers.

   Bitstream: A sequence of bits, in the form of a NAL unit stream or a
   byte stream, that forms the representation of coded pictures and
   associated data forming one or more coded video sequences (CVSs).

   Coded Picture: A coded representation of a picture containing all
   CTUs of the picture.

   Coded Video Sequence (CVS): A sequence of access units that consists,
   in decoding order, of an IDR access unit, followed by zero or more
   access units that are not IDR access units, including all subsequent
   access units up to but not including any subsequent access unit that
   is an IDR access unit.

   Coding Tree Block (CTB): An NxN block of samples for some value of N
   such that the division of a component into CTBs is a partitioning.

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   Coding Tree Unit (CTU): 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 separate colour planes and syntax structures used to code the
   samples.

   Decoded Picture: A decoded picture is derived by decoding a coded
   picture.

   Decoded Picture Buffer (DPB): A buffer holding decoded pictures for
   reference, output reordering, or output delay specified for the
   hypothetical reference decoder in Annex C of [EVC] standard.

   Dynamic Range Adjustment (DRA): A mapping process that is applied to
   decoded picture prior to cropping and output as part of the decoding
   process and is controlled by parameters conveyed in an Adaptation
   Parameter Set (APS).

   Hypothetical Reference Decoder (HRD): A hypothetical decoder model
   that specifies constraints on the variability of conforming NAL unit
   streams or conforming byte streams that an encoding process may
   produce.

   IDR access unit: access unit in which the coded picture is an IDR
   picture.

   IDR picture: coded picture for which each VCL NAL unit has
   NalUnitType equal to IDR_NUT.

   Level: 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 to scaling.

   Network Abstraction Layer (NAL) unit: 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 as necessary.

   Network Abstraction Layer (NAL) Unit Stream: A sequence of NAL units.

   Non-IDR Picture: A coded picture that is not an IDR picture.

   Non-VCL NAL Unit: A NAL unit that is not a VCL NAL unit.

   Picture Parameter Set (PPS): A syntax structure containing syntax
   elements that apply to zero or more entire coded pictures as
   determined by a syntax element found in each slice header.

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   Picture Order Count (POC): A variable that is associated with each
   picture, uniquely identifies the associated picture among all
   pictures in the CVS, and, when the associated picture is to be output
   from the decoded picture buffer, 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 the decoded picture buffer.

   Raw Byte Sequence Payload (RBSP): 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 to 0.

   Sequence Parameter Set (SPS): 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 slice header.

   Slice: integer number of tiles of a picture in the tile scan of the
   picture and that are exclusively contained in a single NAL unit.

   Tile: rectangular region of CTUs within a particular tile column and
   a particular tile row in a picture.

   Tile column: rectangular region of CTUs having a height equal to the
   height of the picture and width specified by syntax elements in the
   PPS.

   Tile row: A rectangular region of CTUs having a height specified by
   syntax elements in the PPS and a width equal to the width of the
   picture.

   Tile scan: A specific sequential ordering of CTUs partitioning a
   picture in which the CTUs are ordered consecutively in CTU raster
   scan in a tile whereas tiles in a picture are ordered consecutively
   in a raster scan of the tiles of the picture.

   Video coding layer (VCL) NAL unit: 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 this document.

3.1.2.  Definitions Specific to This Document

   Media-Aware Network Element (MANE): A network element, such as a
   middlebox, selective forwarding unit, or application-layer gateway
   that is capable of parsing certain aspects of the RTP payload headers
   or the RTP payload and reacting to their contents.

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      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 in
      Section 7 of [RFC3550].

   NAL unit decoding order: A NAL unit order that conforms to the
   constraints on NAL unit order given in Section 7.4.2.3 in [EVC],
   follow the order of NAL units in the bitstream.

   NALU-time: The value that the RTP timestamp would have if the NAL
   unit would be transported in its own RTP packet.

   NAL unit output order: 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 [EVC],
   and in which NAL units within an access unit are in their decoding
   order.

   RTP stream: See [RFC7656].  Within the scope of this document, one
   RTP stream is utilized to transport a EVC bitstream, which may
   contain one or more temporal sub-layers.

   Transmission order: The order of packets in ascending RTP sequence
   number order (in modulo arithmetic).  Within an aggregation packet,
   the NAL unit transmission order is the same as the order of
   appearance of NAL units in the packet.

3.2.  Abbreviations

   AU         Access Unit

   AP         Aggregation Packet

   APS        Adaptation Parameter Set

   ATS        Adaptive Transform Selection

   B          Bi-predictive

   CBR        Constant Bit Rate

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   CPB        Coded Picture Buffer

   CTB        Coding Tree Block

   CTU        Coding Tree Unit

   CVS        Coded Video Sequence

   DPB        Decoded Picture Buffer

   HRD        Hypothetical Reference Decoder

   HSS        Hypothetical Stream Scheduler

   I          Intra

   IDR        Instantaneous Decoding Refresh

   LSB        Least Significant Bit

   LTRP       Long-Term Reference Picture

   MMVD       Merge with Motion Vector Difference

   MSB        Most Significant Bit

   NAL        Network Abstraction Layer

   P          Predictive

   POC        Picture Order Count

   PPS        Picture Parameter Set

   QP         Quantization Parameter

   RBSP       Raw Byte Sequence Payload

   RGB        Same as GBR

   SAR        Sample Aspect Ratio

   SEI        Supplemental Enhancement Information

   SODB       String Of Data Bits

   SPS        Sequence Parameter Set

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   STRP       Short-Term Reference Picture

   VBR        Variable Bit Rate

   VCL        Video Coding Layer

4.  RTP Payload Format

4.1.  RTP Header Usage

   The format of the RTP header is specified in [RFC3550] (reprinted as
   Figure 2 for convenience).  This payload format uses the fields of
   the header in a manner consistent with that specification.

   The RTP payload (and the settings for some RTP header bits) for
   aggregation packets and fragmentation units are specified in
   Section 4.3.2 and Section 4.3.3, respectively.

       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]

                                  Figure 2

   The RTP header information to be set according to this RTP payload
   format is set as follows:

   Marker bit (M): 1 bit

      Set for the last packet of the access unit, carried in the current
      RTP stream.  This is in line with the normal use of the M bit in
      video formats to allow an efficient playout buffer handling.

   Payload Type (PT): 7 bits

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      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.

   Sequence Number (SN): 16 bits

      Set and used in accordance with [RFC3550].

   Timestamp: 32 bits

      The RTP timestamp is set to the sampling timestamp of the content.
      A 90 kHz clock rate MUST be used.  If the NAL unit has no timing
      properties of its own (e.g., parameter sets or certain SEI NAL
      units), the RTP timestamp MUST be set to the RTP timestamp of the
      coded picture of the access unit in which the NAL unit is
      included.  For SEI messages, this information is specified in
      Annex D of [EVC].  Receivers MUST 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 [EVC].

   Synchronization source (SSRC): 32 bits

      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.

4.2.  Payload Header Usage

   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, Reserve and E) as the NAL unit header as shown in
   Section 1.1.4, irrespective of the type of the payload structure.

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

4.3.  Payload Structures

   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.

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   The three different payload structures are as follows:

   *  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 Section 4.3.1.

   *  Aggregation Packet (AP): Contains more than one NAL unit within
      one access unit.  This payload structure is specified in
      Section 4.3.2.

   *  Fragmentation Unit (FU): Contains a subset of a single NAL unit.
      This payload structure is specified in Section 4.3.3.

4.3.1.  Single NAL Unit Packets

   A single NAL unit packet contains exactly one NAL unit, and consists
   of a payload header as defined in Table 4 of [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 Figure 3.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           PayloadHdr          |      DONL (conditional)       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                  NAL unit payload data                        |
     |                                                               |
     |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                               :...OPTIONAL RTP padding        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  The Structure of a Single NAL Unit Packet

                                  Figure 3

   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 Section 7.2 is greater than
   0, the DONL field MUST 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 is equal to 0), the DONL field
   MUST NOT be present.

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4.3.2.  Aggregation Packets (APs)

   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.

   An AP aggregates NAL units of one access unit, and it MUST NOT
   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.

   An AP consists of a payload header, as defined in Table 4 of [EVC]
   (denoted here as PayloadHdr with Type=56) followed by two or more
   aggregation units, as shown in Figure 4.

     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

                                  Figure 4

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

   The value of TID MUST be the smallest value of TID of all the
   aggregated NAL units.  The value of Reserve and E MUST be equal to 0
   for this specification.

      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 same AP.

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   An AP MUST carry at least two aggregation units and can carry as many
   aggregation units as necessary; however, the total amount of data in
   an AP obviously MUST fit into an IP packet, and the size SHOULD be
   chosen so that the resulting IP packet is smaller than the path MTU
   size so to avoid IP layer fragmentation.  An AP MUST NOT contain FUs
   specified in Section 4.3.3.  APs MUST NOT be nested; i.e., an AP can
   not contain another AP.

      Informative note: If a receiver encounters nested Aggregation
      Packets, which is against the aforementioned requirement, it has
      several options, listed in order of ease of implementation: 1)
      Ignore the nested AP; 2) Ignore the nested AP and report a "packet
      loss" to the decoder, if such functionality exists in the API, 3)
      Implement support for nested APs and extract the Network
      Abstraction Layer (NAL) units from these nested APs.

   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 Figure 5.

     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

                                  Figure 5

      Informative note: The first octet of Figure 5 (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 octet boundary.

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

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   If sprop-max-don-diff is greater than 0, the DONL field MUST 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 variable 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 is equal to 0), the DONL field MUST NOT be
   present in an aggregation unit that is the first aggregation unit in
   an AP

   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 Figure 6.

     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

                                  Figure 6

      Informative note: The first octet of Figure 6 (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 octet boundary.

   Figure 7 presents an example of an AP that contains two aggregation
   units, labeled as NALU 1 and NALU 2 in the figure, without the DONL
   field being present.

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     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

                                  Figure 7

   Figure 8 presents an example of an AP that contains two aggregation
   units, labeled as NALU 1 and NALU 2 in the figure, with the DONL
   field being present.

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     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

                                  Figure 8

4.3.3.  Fragmentation Units

   Fragmentation Units (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 unit MUST 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).

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

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

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   An FU consists of a payload header as defined in Table 4 of [EVC]
   (denoted as PayloadHdr with type=57), an FU header of one octet, a
   conditional 16-bit DONL field (in network byte order), and an FU
   payload, as shown in Figure 9.

     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

                                  Figure 9

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

   The FU header consists of an S bit, an E bit, and a 6-bit FuType
   field, as shown in Figure 10.

                              0 1 2 3 4 5 6 7
                             +-+-+-+-+-+-+-+-+
                             |S|E|  FuType   |
                             +---------------+

                         The Structure of FU Header

                                 Figure 10

   The semantics of the FU header fields are as follows:

   S: 1 bit

      When set to 1, the S bit indicates the start of a fragmented NAL
      unit, i.e., the first byte of the FU payload is also the first
      byte of the payload of the fragmented NAL unit.  When the FU
      payload is not the start of the fragmented NAL unit payload, the S
      bit MUST be set to 0.

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   E: 1 bit

      When set to 1, the E bit indicates the end of a fragmented NAL
      unit, i.e., the last byte of the payload is also the last byte of
      the fragmented NAL unit.  When the FU payload is not the last
      fragment of a fragmented NAL unit, the E bit MUST be set to 0.

   FuType: 6 bits

      The field FuType MUST be equal to the field Type of the fragmented
      NAL unit.

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

   If sprop-max-don-diff is greater than 0, and the S bit is equal to 1,
   the DONL field MUST 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 is equal to 0, or the S bit is
   equal to 0), the DONL field MUST NOT be present in the FU.

   A non-fragmented NAL unit MUST NOT be transmitted in one FU; i.e.,
   the Start bit and End bit MUST NOT both be set to 1 in the same FU
   header.

   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 FU payload, but
   rather the information of the NAL unit header of the fragmented NAL
   unit is conveyed in F, TID, Reserve and E fields of the FU payload
   headers of the FUs and the FuType field of the FU header of the FUs.
   An FU payload MUST NOT be empty.

   If an FU is lost, the receiver SHOULD 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.

   A receiver in an endpoint or a MANE MAY 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 unit MUST be set to 1 to indicate a
   syntax violation.

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4.4.  Decoding Order Number

   For each NAL unit, the variable AbsDon is derived, representing the
   decoding order number that is indicative of the NAL unit decoding
   order.

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

   If sprop-max-don-diff is equal to 0, AbsDon[n], the value of AbsDon
   for NAL unit n, is derived as equal to n.

   Otherwise (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:

   *  If n is equal to 0 (i.e., NAL unit n is the very first NAL unit in
      transmission order), AbsDon[0] is set equal to DON[0].

   *  Otherwise (n is greater than 0), the following applies for
      derivation of AbsDon[n]:

         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])

   For any two NAL units m and n, the following applies:

   *  AbsDon[n] greater than AbsDon[m] indicates that NAL unit n follows
      NAL unit m in NAL unit decoding order.

   *  When AbsDon[n] is equal to AbsDon[m], the NAL unit decoding order
      of the two NAL units can be in either order.

   *  AbsDon[n] less than AbsDon[m] indicates that NAL unit n precedes
      NAL unit m in decoding order.

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         Informative note: When two consecutive NAL units in the NAL
            unit decoding order has different values of AbsDon, the the
            absolute difference between the two AbsDon values may be
            greater than or equal to 1.

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

5.  Packetization Rules

   The following packetization rules apply:

   *  If sprop-max-don-diff is greater than 0, the transmission order of
      NAL units carried in the RTP stream MAY be different from the NAL
      unit decoding order.  Otherwise (sprop-max-don-diff equals 0), the
      transmission order of NAL units carried in the RTP stream MUST be
      the same as the NAL unit decoding order.

   *  A NAL unit of small size SHOULD be encapsulated in an aggregation
      packet together with one or more other NAL units to avoid the
      unnecessary packetization overhead for small NAL units.  For
      example, non-VCL NAL units, such as access unit delimiters,
      parameter sets, or SEI NAL units, are typically small and can
      often be aggregated with VCL NAL units without violating MTU size
      constraints.

   *  Each non-VCL NAL unit SHOULD, when possible from an MTU size match
      viewpoint, be encapsulated in an aggregation packet with its
      associated VCL NAL unit, as typically, a non-VCL NAL unit would be
      meaningless without the associated VCL NAL unit being available.

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   *  For carrying precisely one NAL unit in an RTP packet, a single NAL
      unit packet MUST be used.

6.  De-packetization Process

   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.

   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.

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

   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 be passed to the decoder.

   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
   the de-packetization buffer.  Receivers should also prepare for
   transmission delay jitter; that is, either reserve separate buffers
   for transmission delay jitter buffering and de-packetization
   buffering or use a receiver buffer for both transmission 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 starting of decoding and
   playback.

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   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 an aggregation packet, 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 Section 4.3.2.  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 Section 4.3.3.

   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.

   When sprop-max-don-diff is greater than 0, the process described in
   the remainder of this section applies.

   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.

   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.

   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.

   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:

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   *  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.

   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.

7.  Payload Format Parameters

   This section specifies the optional parameters.  A mapping of the
   parameters with Session Description Protocol (SDP) [RFC8866] is also
   provided for applications that use SDP.

   Parameters starting with the string "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" parameters
   are being sent.  This uncommon characteristic of the "sprop"
   parameters may not be intuitive in the context of some signaling
   protocol concepts, especially with offer/answer.  Please see
   Section 7.3.2 for guidance specific to the use of sprop parameters in
   the Offer/Answer case.

7.1.  Media Type Registration

   The receiver MUST ignore any parameter unspecified in this document.

   Type name:            video

   Subtype name:         evc

   Required parameters: N/A

   Optional parameters: 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 Section 7.2 for
   definitions)

   Encoding considerations:

      This type is only defined for transfer via RTP (RFC 3550).

   Security considerations:

      See Section 9 of RFC XXXX.

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   Interoperability considerations: N/A

   Published specification:

      Please refer to RFC XXXX and EVC standard [EVC].

   Applications that use this media type:

      Any application that relies on EVC-based video services over RTP

   Fragment identifier considerations: N/A

   Additional information: N/A

   Person & email address to contact for further information:

      Stephan Wenger (stewe@stewe.org)

   Intended usage: COMMON

   Restrictions on usage: N/A

   Author: See Authors' Addresses section of RFC XXXX.

   Change controller:

      IETF <avtcore@ietf.org>

7.2.  Optional Parameters Definition

   profile-id, level-id, toolset-id:

      These parameters indicate the profile, the level, and constraints
      of the bitstream carried by the RTP stream, or a specific set of
      the profile, the level, and constraints the receiver supports.

      More specifications of these parameters, including how they relate
      to syntax elements specified in [EVC] are provided below.

   profile-id:

      When profile-id is not present, a value of 0 (i.e., the Baseline
      profile) MUST be inferred.

      When used to indicate properties of a bitstream, profile-id MUST
      be derived from the profile_idc in the SPS.

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

   level-id:

      When level-id is not present, a value of 90 (corresponding to
      level 3, which allows for approximately SD TV resolution and frame
      rates; for details please see Annex A of EVC) MUST be inferred.

      When used to indicate properties of a bitstream, level-id MUST be
      derived from the level_idc in the SPS.

      If the level-id parameter is used for capability exchange, the
      following applies.  If max-recv-level-id is not present, the
      default level defined by level-id indicates the highest level the
      codec wishes to support.  Otherwise, max-recv-level-id indicates
      the highest level the codec supports for receiving.  For either
      receiving or sending, all levels that are lower than the highest
      level supported MUST also be supported.

   toolset-id:

      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.  When used to indicate properties
      of a bitstream, its value MUST be derived from toolset_idh_h and
      toolset_idc_l in the sequence parameter set.

   max-recv-level-id:

      This parameter MAY be used to indicate the highest level a
      receiver supports.

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

   When max-recv-level-id is not present, the value is inferred to be
   equal to level-id.

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   max-recv-level-id MUST NOT be present when the highest level the
   receiver supports is not higher than the default level.

   sprop-sps:

      This parameter MAY 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 of base64 encoding (Section 4 of [RFC4648])
      representations of the sequence parameter set NAL units as
      specified in Section 7.3.2.1 of [EVC].

   sprop-pps:

      This parameter MAY be used to convey picture parameter set NAL
      units of the bitstream for out-of-band transmission of picture
      parameter sets.  The value of the parameter is a comma-separated
      (',') list of base64 encoding (Section 4 of [RFC4648])
      representations of the picture parameter set NAL units as
      specified in Section 7.3.2.2 of [EVC].

   sprop-sei:

      This parameter MAY be used to convey one or more SEI messages that
      describe bitstream characteristics.  When present, a decoder can
      rely on the bitstream 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
      [VSEI].

      The value of the parameter is a comma-separated (',') list of
      base64 encoding (Section 4 of [RFC4648]) representations of SEI
      NAL units as specified in [VSEI].

      Informative note: Intentionally, no list of applicable or
         inapplicable SEI messages is specified here.  Conveying certain
         SEI messages in sprop-sei may be sensible in some application
         scenarios and meaningless in others.  However, a few examples
         are described below:

      1) In an environment where the bitstream was created from film-
         based source material, and no splicing is going to occur during
         the lifetime of the session, the film grain characteristics SEI
         message is likely meaningful, and sending it in sprop-sei
         rather than in the bitstream at each entry point may help with
         saving bits and allows one to configure the renderer only once,
         avoiding unwanted artifacts.

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      2) Examples for SEI messages that would be meaningless to be
         conveyed in sprop-sei include the decoded picture hash SEI
         message (it is close to impossible that all decoded pictures
         have the same hashtag) or the filler payload SEI message (as
         there is no point in just having more bits in SDP).

   sprop-max-don-diff:

      If there is no NAL unit naluA that is followed in transmission
      order by any NAL unit preceding naluA in decoding order (i.e., the
      transmission order of the NAL units is the same as the decoding
      order), the value of this parameter MUST be equal to 0.

      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.

      The value of sprop-max-don-diff MUST be an integer in the range of
      0 to 32767, inclusive.

      When not present, the value of sprop-max-don-diff is inferred to
      be equal to 0.

   sprop-depack-buf-bytes:

      This parameter signals the required size of the de-packetization
      buffer in units of bytes.  The value of the parameter MUST be
      greater than or equal to the maximum buffer occupancy (in units of
      bytes) of the de-packetization buffer as specified in Section 6.

      The value of sprop-depack-buf-bytes MUST be an integer in the
      range of 0 to 4294967295, inclusive.

      When sprop-max-don-diff is present and greater than 0, this
      parameter MUST be present and the value MUST be greater than 0.
      When not present, the value of sprop-depack-buf-bytes is inferred
      to be equal to 0.

      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.

   depack-buf-cap:

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      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.

      When not present, the value of depack-buf-cap is inferred to be
      equal to 4294967295.  The value of depack-buf-cap MUST be an
      integer in the range of 1 to 4294967295, inclusive.

      Informative note: depack-buf-cap indicates the maximum possible
         size of the de-packetization buffer of the receiver only,
         without allowing for network jitter.

7.3.  SDP Parameters

   The receiver MUST ignore any parameter unspecified in this document.

7.3.1.  Mapping of Payload Type Parameters to SDP

   The media type video/evc string is mapped to fields in the Session
   Description Protocol (SDP) [RFC8866] as follows:

   *  The media name in the "m=" line of SDP MUST be video.

   *  The encoding name in the "a=rtpmap" line of SDP MUST be evc (the
      media subtype).

   *  The clock rate in the "a=rtpmap" line MUST be 90000.

   *  The OPTIONAL parameters profile-id, level-id, toolset-id, max-
      recv-level-id, sprop-max-don-diff, sprop-depack-buf-bytes, and
      depack-buf-cap, when present, MUST be included in the "a=fmtp"
      line of SDP.  The fmtp line is expressed as a media type string,
      in the form of a semicolon-separated list of parameter=value
      pairs.

   *  The OPTIONAL parameters sprop-sps, sprop-pps, and sprop-sei, when
      present, MUST be included in the "a=fmtp" line of SDP or conveyed
      using the "fmtp" source attribute as specified in Section 6.3 of
      [RFC5576].  For a particular media format (i.e., RTP payload
      type), sprop-sps, sprop-pps, or sprop-sei MUST NOT be both
      included in the "a=fmtp" line of SDP and conveyed using the "fmtp"
      source attribute.  When included in the "a=fmtp" line of SDP,
      those parameters are expressed as a media type string, in the form
      of a semicolon-separated list of parameter=value pairs.  When

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      conveyed in the "a=fmtp" line of SDP for a particular payload
      type, the parameters sprop-sps, sprop-pps, and sprop-sei MUST be
      applied to each SSRC with the payload type.  When conveyed using
      the "fmtp" source attribute, these parameters are only associated
      with the given source and payload type as parts of the "fmtp"
      source attribute.

      Informative note: Conveyance of sprop-sps and sprop-pps using the
      "fmtp" source attribute allows for out-of-band transport of
      parameter sets in topologies like Topo-Video-switch-MCU, as
      specified in [RFC7667].

   A general usage of media representation in SDP is as follows:

           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>;

   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.

     Offerer->Answerer:
           m=video 49170 RTP/AVP 98
           a=rtpmap:98 evc/90000
           a=fmtp:98 profile-id=1; level_id=90;

      The above represents an offer for symmetric video communication
      using [EVC] and its payload specification at the main profile and
      level 3.0.  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 [EVC].  At the
      same time, if this offer were accepted "as is", the offer can
      expect that the answerer would be able to receive and properly
      decode EVC media up to and including level 3.0.

     Answerer->Offerer:
           m=video 49170 RTP/AVP 98
           a=rtpmap:98 evc/90000
           a=fmtp:98 profile-id=1; level_id=60

      Informative note: level_id shall be set equal to a value of 30
         times the level number specified in Table A.1 of EVC.

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   With this answer to the offer above, the system receiving the offer
   advises the offerer that it is incapable of handing evc at level 3.0
   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.

7.3.2.  Usage with SDP Offer/Answer Model

   This section describes the negotiation of unicast messages using the
   offer/answer model described in [RFC3264] and its updates.

   This section applies to all profiles defined in [EVC], specifically
   to Baseline, Main, and the associated still image profiles.

   The following limitations and rules pertaining to the media
   configuration apply:

   The parameters identifying a media format configuration for EVC are
   profile-id and level-id.  Profile_id MUST be used symmetrically.

   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).

   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
   Section 7.3.2.1 (Payload format config) below.

   To simplify handling and matching of these configurations, the same
   RTP payload type number used in the offer SHOULD also be used in the
   answer, as specified in [RFC3264].

   The answer MUST NOT 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.

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7.3.2.1.  Payload Format Configuration

   The following limitations and rules pertain to the configuration of
   the payload format buffer management.

   The parameters sprop-max-don-diff and sprop-depack-buf-bytes describe
   the properties of an RTP stream that the offerer or the answerer is
   sending for the media format configuration.  This differs from the
   normal usage of the offer/answer parameters; normally, such
   parameters declare the properties of the bitstream or RTP stream that
   the offerer or the answerer is able to receive.  When dealing with
   EVC, the offerer assumes that the answerer will be able to receive
   media encoded using the configuration being offered.

   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 the configuration.

   When an offerer offers an interleaved stream, indicated by the
   presence of sprop-max-don-diff with a value larger than zero, the
   offerer MUST include the size of the de-packetization buffer sprop-
   depack-buf-bytes.

   To enable the offerer and answerer to inform each other about their
   capabilities for de-packetization buffering in receiving RTP streams,
   both parties are RECOMMENDED to include depack-buf-cap.

   The parameters sprop-sps, or sprop-pps, when present (included in the
   "a=fmtp" line of SDP or conveyed using the "fmtp" source attribute,
   as specified in Section 6.3 of [RFC5576]), are used for out-of-band
   transport of the parameter sets (SPS or PPS, respectively).  The
   answerer MAY use either out-of-band or in-band transport of parameter
   sets for the bitstream it is sending, regardless of whether out-of-
   band parameter sets transport has been used in the offerer-to-
   answerer direction.  Parameter sets included in an answer are
   independent of those parameter sets included in the offer, as they
   are used for decoding two different bitstreams; one from the answerer
   to the offerer and the other in the opposite direction.  In case some
   RTP packets are sent before the SDP offer/answer settles down, in-
   band parameter sets MUST be used for those RTP stream parts sent
   before the SDP offer/answer.

   The following rules apply to transport of parameter sets in the
   offerer-to-answerer direction.

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   An offer MAY include sprop-sps, and/or sprop-pps.  If none of these
   parameters are present in the offer, then only in-band transport of
   parameter sets is used.

   If the level to use in the offerer-to-answerer direction is equal to
   the default level in the offer, the answerer MUST be prepared to use
   the parameter sets included in sprop-sps, and sprop-pps (either
   included in the "a=fmtp" line of SDP or conveyed using the "fmtp"
   source attribute) for decoding the incoming bitstream, e.g., by
   passing these parameter set NAL units to the video decoder before
   passing any NAL units carried in the RTP streams.  Otherwise, the
   answerer MUST ignore sprop-vps, sprop-sps, and sprop-pps (either
   included in the "a=fmtp" line of SDP or conveyed using the "fmtp"
   source attribute) and the offerer MUST transmit parameter sets in-
   band.

   The following rules apply to transport of parameter sets in the
   answerer-to-offerer direction.

   An answer MAY include sprop-sps, and/or sprop-pps.  If none of these
   parameters are present in the answer, then only in-band transport of
   parameter sets is used.

   The offerer MUST be prepared to use the parameter sets included in
   sprop-sps and sprop-pps (either included in the "a=fmtp" line of SDP
   or conveyed using the "fmtp" source attribute) for decoding the
   incoming bitstream, e.g., by passing these parameter set NAL units to
   the video decoder before passing any NAL units carried in the RTP
   streams.

   When sprop-sps and/or sprop-pps are conveyed using the "fmtp" source
   attribute, as specified in Section 6.3 of [RFC5576], the receiver of
   the parameters MUST store the parameter sets included in sprop-sps
   and/or sprop-pps and associate them with the source given as part of
   the "fmtp" source attribute.  Parameter sets associated with one
   source (given as part of the "fmtp" source attribute) MUST only be
   used to decode NAL units conveyed in RTP packets from the same source
   (given as part of the "fmtp" source attribute).  When this mechanism
   is in use, SSRC collision detection and resolution MUST be performed
   as specified in [RFC5576].

   Figure 11 lists the interpretation of all the parameters that MAY be
   used for the various combinations of offer, answer, and direction
   attributes.

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                                    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: changeable 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 being
       consistent-basically, level down-grading is allowed)

    P: properties of the bitstream to be sent
    R: receiver capabilities
    -: not usable, when present MUST be ignored

   Interpretation of Parameters for Various Combinations of
   Offers, Answers, and Direction Attributes.

                                 Figure 11

   Parameters used for declaring receiver capabilities are, in general,
   downgradable, i.e., they express the upper limit for a sender's
   possible behavior.  Thus, a sender MAY select to set its encoder
   using only lower/lesser or equal values of these parameters.

   When a sender's capabilities are declared with the configuration
   parameters, these parameters express a configuration that is
   acceptable for the sender to receive bitstreams.  In order to achieve
   high interoperability levels, it is often advisable to offer multiple
   alternative configurations.  It is 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.

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   An implementation SHOULD be able to understand all media type
   parameters (including all optional media type parameters), even if it
   doesn'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 can cope, leading to
   higher chances of interoperability beyond the most basic interop
   points (for which, as described above, no optional parameters are
   necessary).

   Informative note: In implementations of various H.26x video coding
   payload Formats including those for [AVC] and [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, the offer/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-based offer/answer process, of
   the capabilities of the involved systems (walled gardens, baseline
   requirements defined in application standards higher up in the stack,
   and similar).

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

7.3.3.  Multicast

   For bitstreams being delivered over multicast, the following rules
   apply:

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

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   To simplify the handling and matching of these configurations, the
   same RTP payload type number used in the offer SHOULD also be used in
   the answer, as specified in [RFC3264].  An answer MUST NOT contain a
   payload type number used in the offer unless the configuration is the
   same as in the offer.

   Parameter sets received MUST be associated with the originating
   source and MUST only be used in decoding the incoming bitstream from
   the same source.

   The rules for other parameters are the same as above for unicast as
   long as the three above rules are obeyed.

7.3.4.  Usage in Declarative Session Descriptions

   When EVC over RTP is offered with SDP in a declarative style, as in
   Real Time Streaming Protocol (RTSP) [RFC7826] or Session Announcement
   Protocol (SAP) [RFC2974], the following considerations apply.

   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 parameters MUST be used:

   Declaring actual configuration or bitstream properties:

   profile-id level-id sprop-sps sprop-pps sprop-max-don-diff sprop-
   depack-buf-bytes sprop-sei

   Not usable (when present, they MUST be ignored):

   depack-buf-cap recv-sublayer-id

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

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7.3.5.  Considerations for Parameter Sets

   When out-of-band transport of parameter sets is used, parameter sets
   MAY 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.

8.  Use with Feedback Messages

   The following subsections define the use of the Picture Loss
   Indication (PLI) and Full Intra Request (FIR) feedback messages with
   [EVC].  The PLI is defined in [RFC4585], and the FIR message is
   defined in [RFC5104].

   In accordance with this document, a sender MUST NOT send Slice Loss
   Indication (SLI) or Reference Picture Selection Indication (RPSI),
   and a receiver MUST ignore RPSI and MUST treat a received SLI as a
   received PLI, ignoring the "First", "Number", and "PictureID" fields
   of the PLI.

8.1.  Picture Loss Indication (PLI)

   As specified in Section 6.3.1 of [RFC4585], the reception of a PLI by
   a media sender indicates "the loss of an undefined amount of coded
   video data belonging to one or more pictures".  Without having any
   specific knowledge of the setup of the bitstream (such as use and
   location of in-band parameter sets, IDR picture locations, picture
   structures, and so forth), a reaction to the reception of a PLI by a
   EVC sender SHOULD be to send an IDR picture and relevant parameter
   sets, potentially with sufficient redundancy so to ensure 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 and
   congestion control mechanisms of [RFC4585] MUST be observed.

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8.2.  Full Intra Request (FIR)

   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 [RFC8082].

   Upon reception of a FIR, a sender MUST send an IDR picture.
   Parameter sets MUST 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.

9.  Security Considerations

   The scope of this section is limited to the payload format itself and
   to one feature of [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 Considerations section in
   [RFC3550]) and the security of the call-control stack chosen (that
   may make use of the media type registration of this document).
   Implementers should also consider known security vulnerabilities of
   video coding and decoding implementations in general and avoid those.

   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.

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   RTP packets using the payload format defined in this specification
   are subject to the security considerations discussed in the RTP
   specification [RFC3550], and in any applicable RTP profile such as
   RTP/AVP [RFC3551], RTP/AVPF [RFC4585], RTP/SAVP [RFC3711], or RTP/
   SAVPF [RFC5124].  However, as "Securing the RTP Framework: Why RTP
   Does Not Mandate a Single Media Security Solution" [RFC7202]
   discusses, it is not an RTP payload format's responsibility to
   discuss or mandate what solutions are used to meet the basic security
   goals like confidentiality, integrity and source authenticity for RTP
   in general.  This responsibility lays on anyone using RTP in an
   application.  They can find guidance on available security mechanisms
   and important considerations in "Options for Securing RTP Sessions"
   [RFC7201].  Applications SHOULD use one or more appropriate strong
   security mechanisms.  The rest of this section discusses the security
   impacting properties of the payload format itself.

   Because the data compression used with this payload format is applied
   end-to-end, any encryption needs to be performed after compression.
   A potential denial-of-service threat exists for data encodings using
   compression techniques that 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.

   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 is RECOMMENDED based on the thoughts of [RFC7202].

   Like HEVC [RFC7798] and [VVC], [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.

   [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 a web-browser unchecked would be a bad and
   insecure implementation practice.  The safest way to deal with user
   data SEI messages is to simply discard them, but that can have
   negative side effects on the quality of experience by the user.

   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

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   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.

10.  Congestion Control

   Congestion control for RTP SHALL be used in accordance with RTP
   [RFC3550] and with any applicable RTP profile, e.g., AVP [RFC3551] or
   AVPF [RFC4585].  If best-effort service is being used, an additional
   requirement is that users of this payload format MUST monitor packet
   loss to ensure that the packet loss rate is within an acceptable
   range.  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.  This
   condition can be satisfied by implementing congestion-control
   mechanisms to adapt the transmission rate, by implementing the number
   of layers subscribed for a layered multicast session, or by arranging
   for a receiver to leave the session if the loss rate is unacceptably
   high.

   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.

   The key mechanism available in [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.

   The mechanisms mentioned above generally work within a defined
   profile and level; therefore no renegotiation of the channel is
   required.  Only when non-downgradable parameters (such as profile)
   are required to be changed does it become necessary to terminate and
   restart the RTP stream(s).  This may be accomplished by using
   different RTP payload types.

   MANEs MAY 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 the MANE's
   viewpoint) experiences congestion.

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11.  IANA Considerations

   A new media type, as specified in Section 7.1 of this document, has
   been registered with IANA.

12.  Acknowledgements

   Large parts of this specification share text with the RTP payload
   format for VVC [RFC9328].  Roman Chernyak is thanksed for his
   valueable review comments.  We thank the authors of that
   specification for their excellent work.

13.  References

13.1.  Normative References

   [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>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              DOI 10.17487/RFC3264, June 2002,
              <https://www.rfc-editor.org/rfc/rfc3264>.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
              July 2003, <https://www.rfc-editor.org/rfc/rfc3550>.

   [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
              Video Conferences with Minimal Control", STD 65, RFC 3551,
              DOI 10.17487/RFC3551, July 2003,
              <https://www.rfc-editor.org/rfc/rfc3551>.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, DOI 10.17487/RFC3711, March 2004,
              <https://www.rfc-editor.org/rfc/rfc3711>.

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   [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
              "Extended RTP Profile for Real-time Transport Control
              Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
              DOI 10.17487/RFC4585, July 2006,
              <https://www.rfc-editor.org/rfc/rfc4585>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/rfc/rfc4648>.

   [RFC5104]  Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
              "Codec Control Messages in the RTP Audio-Visual Profile
              with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104,
              February 2008, <https://www.rfc-editor.org/rfc/rfc5104>.

   [RFC5124]  Ott, J. and E. Carrara, "Extended Secure RTP Profile for
              Real-time Transport Control Protocol (RTCP)-Based Feedback
              (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February
              2008, <https://www.rfc-editor.org/rfc/rfc5124>.

   [RFC5576]  Lennox, J., Ott, J., and T. Schierl, "Source-Specific
              Media Attributes in the Session Description Protocol
              (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009,
              <https://www.rfc-editor.org/rfc/rfc5576>.

   [RFC7826]  Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M.,
              and M. Stiemerling, Ed., "Real-Time Streaming Protocol
              Version 2.0", RFC 7826, DOI 10.17487/RFC7826, December
              2016, <https://www.rfc-editor.org/rfc/rfc7826>.

   [RFC8082]  Wenger, S., Lennox, J., Burman, B., and M. Westerlund,
              "Using Codec Control Messages in the RTP Audio-Visual
              Profile with Feedback with Layered Codecs", RFC 8082,
              DOI 10.17487/RFC8082, March 2017,
              <https://www.rfc-editor.org/rfc/rfc8082>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [RFC8866]  Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP:
              Session Description Protocol", RFC 8866,
              DOI 10.17487/RFC8866, January 2021,
              <https://www.rfc-editor.org/rfc/rfc8866>.

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   [RFC9328]  Zhao, S., Wenger, S., Sanchez, Y., Wang, Y.-K., and M. M.
              Hannuksela, "RTP Payload Format for Versatile Video Coding
              (VVC)", RFC 9328, DOI 10.17487/RFC9328, December 2022,
              <https://www.rfc-editor.org/rfc/rfc9328>.

   [VSEI]     "Versatile supplemental enhancement information messages
              for coded video bitstreams", 2020,
              <https://www.itu.int/rec/T-REC-H.274>.

13.2.  Informative References

   [AVC]      "ITU-T Recommendation H.264 - Advanced video coding for
              generic audiovisual services", 2014,
              <https://www.iso.org/standard/66069.html>.

   [HEVC]     "High efficiency video coding, ITU-T Recommendation
              H.265", 2019, <https://www.itu.int/rec/T-REC-H.265>.

   [MPEG2S]   IS0/IEC, "Information technology - Generic coding ofmoving
              pictures and associated audio information - Part
              1:Systems, ISO International Standard 13818-1", 2013.

   [RFC2974]  Handley, M., Perkins, C., and E. Whelan, "Session
              Announcement Protocol", RFC 2974, DOI 10.17487/RFC2974,
              October 2000, <https://www.rfc-editor.org/rfc/rfc2974>.

   [RFC6184]  Wang, Y.-K., Even, R., Kristensen, T., and R. Jesup, "RTP
              Payload Format for H.264 Video", RFC 6184,
              DOI 10.17487/RFC6184, May 2011,
              <https://www.rfc-editor.org/rfc/rfc6184>.

   [RFC6190]  Wenger, S., Wang, Y.-K., Schierl, T., and A.
              Eleftheriadis, "RTP Payload Format for Scalable Video
              Coding", RFC 6190, DOI 10.17487/RFC6190, May 2011,
              <https://www.rfc-editor.org/rfc/rfc6190>.

   [RFC7201]  Westerlund, M. and C. Perkins, "Options for Securing RTP
              Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014,
              <https://www.rfc-editor.org/rfc/rfc7201>.

   [RFC7202]  Perkins, C. and M. Westerlund, "Securing the RTP
              Framework: Why RTP Does Not Mandate a Single Media
              Security Solution", RFC 7202, DOI 10.17487/RFC7202, April
              2014, <https://www.rfc-editor.org/rfc/rfc7202>.

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   [RFC7656]  Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and
              B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms
              for Real-Time Transport Protocol (RTP) Sources", RFC 7656,
              DOI 10.17487/RFC7656, November 2015,
              <https://www.rfc-editor.org/rfc/rfc7656>.

   [RFC7667]  Westerlund, M. and S. Wenger, "RTP Topologies", RFC 7667,
              DOI 10.17487/RFC7667, November 2015,
              <https://www.rfc-editor.org/rfc/rfc7667>.

   [RFC7798]  Wang, Y.-K., Sanchez, Y., Schierl, T., Wenger, S., and M.
              M. Hannuksela, "RTP Payload Format for High Efficiency
              Video Coding (HEVC)", RFC 7798, DOI 10.17487/RFC7798,
              March 2016, <https://www.rfc-editor.org/rfc/rfc7798>.

   [VVC]      "Versatile Video Coding, ITU-T Recommendation H.266",
              2020, <http://www.itu.int/rec/T-REC-H.266>.

Authors' Addresses

   Shuai Zhao
   Intel
   2200 Mission College Blvd
   Santa Clara,  95054
   United States of America
   Email: shuai.zhao@ieee.org

   Stephan Wenger
   Tencent
   2747 Park Blvd
   Palo Alto,  94588
   United States of America
   Email: stewe@stewe.org

   Youngkwon Lim
   Samsung Electronics
   6625 Excellence Way
   Plano,  75013
   United States of America
   Email: yklwhite@gmail.com

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