idnits 2.17.1 draft-ietf-payload-rtp-h265-03.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** There are 3 instances of too long lines in the document, the longest one being 14 characters in excess of 72. ** The abstract seems to contain references ([HEVC]), which it shouldn't. Please replace those with straight textual mentions of the documents in question. == There are 2 instances of lines with non-RFC6890-compliant IPv4 addresses in the document. If these are example addresses, they should be changed. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 1346 has weird spacing: '...L unit into ...' == Line 3279 has weird spacing: '...UST be set ...' == Line 3280 has weird spacing: '...ntation of t...' == Line 3304 has weird spacing: '...k-sized video...' == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: 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, LayerId, and TID 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. -- The document date (April 30, 2014) is 3649 days in the past. Is this intentional? 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'HEVC' ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) == Outdated reference: A later version (-11) exists of draft-ietf-avtcore-rtp-multi-stream-01 == Outdated reference: A later version (-54) exists of draft-ietf-mmusic-sdp-bundle-negotiation-05 == Outdated reference: A later version (-08) exists of draft-ietf-avtext-rtp-grouping-taxonomy-01 Summary: 5 errors (**), 0 flaws (~~), 22 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Y.-K. Wang 2 Internet Draft Qualcomm 3 Intended status: Standards track Y. Sanchez 4 Expires: October 2014 T. Schierl 5 Fraunhofer HHI 6 S. Wenger 7 Vidyo 8 M. M. Hannuksela 9 Nokia 10 April 30, 2014 12 RTP Payload Format for High Efficiency Video Coding 13 draft-ietf-payload-rtp-h265-03.txt 15 Abstract 17 This memo describes an RTP payload format for the video coding 18 standard ITU-T Recommendation H.265 and ISO/IEC International 19 Standard 23008-2, both also known as High Efficiency Video Coding 20 (HEVC) [HEVC] and developed by the Joint Collaborative Team on Video 21 Coding (JCT-VC). The RTP payload format allows for packetization of 22 one or more Network Abstraction Layer (NAL) units in each RTP packet 23 payload, as well as fragmentation of a NAL unit into multiple RTP 24 packets. Furthermore, it supports transmission of an HEVC bitstream 25 over a single as well as multiple RTP streams. The payload format 26 has wide applicability in videoconferencing, Internet video 27 streaming, and high bit-rate entertainment-quality video, among 28 others. 30 Status of this Memo 32 This Internet-Draft is submitted to IETF in full conformance with 33 the provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF), its areas, and its working groups. Note that 37 other groups may also distribute working documents as Internet- 38 Drafts. 40 Internet-Drafts are draft documents valid for a maximum of six 41 months and may be updated, replaced, or obsoleted by other documents 42 at any time. It is inappropriate to use Internet-Drafts as 43 reference material or to cite them other than as "work in progress." 45 The list of current Internet-Drafts can be accessed at 46 http://www.ietf.org/ietf/1id-abstracts.txt. 48 The list of Internet-Draft Shadow Directories can be accessed at 49 http://www.ietf.org/shadow.html. 51 This Internet-Draft will expire on October 30, 2014. 53 Copyright and License Notice 55 Copyright (c) 2014 IETF Trust and the persons identified as the 56 document authors. All rights reserved. 58 This document is subject to BCP 78 and the IETF Trust's Legal 59 Provisions Relating to IETF Documents 60 (http://trustee.ietf.org/license-info) in effect on the date of 61 publication of this document. Please review these documents 62 carefully, as they describe your rights and restrictions with 63 respect to this document. Code Components extracted from this 64 document must include Simplified BSD License text as described in 65 Section 4.e of the Trust Legal Provisions and are provided without 66 warranty as described in the Simplified BSD License. 68 Table of Contents 70 Abstract..........................................................1 71 Status of this Memo...............................................1 72 Table of Contents.................................................3 73 1 . Introduction..................................................5 74 1.1 . Overview of the HEVC Codec...............................5 75 1.1.1 Coding-Tool Features..................................5 76 1.1.2 Systems and Transport Interfaces......................7 77 1.1.3 Parallel Processing Support..........................14 78 1.1.4 NAL Unit Header......................................16 79 1.2 . Overview of the Payload Format..........................17 80 2 . Conventions..................................................18 81 3 . Definitions and Abbreviations................................18 82 3.1 Definitions...............................................18 83 3.1.1 Definitions from the HEVC Specification..............18 84 3.1.2 Definitions Specific to This Memo....................20 85 3.2 Abbreviations.............................................22 86 4 . RTP Payload Format...........................................23 87 4.1 RTP Header Usage..........................................23 88 4.2 Payload Header Usage......................................26 89 4.3 Payload Structures........................................26 90 4.4 Transmission Modes........................................27 91 4.5 Decoding Order Number.....................................28 92 4.6 Single NAL Unit Packets...................................30 93 4.7 Aggregation Packets (APs).................................31 94 4.8 Fragmentation Units (FUs).................................35 95 4.9 PACI packets..............................................38 96 4.9.1 Reasons for the PACI rules (informative).............41 97 4.9.2 PACI extensions (Informative)........................41 98 4.10 Temporal Scalability Control Information.................43 99 5 . Packetization Rules..........................................45 100 6 . De-packetization Process.....................................45 101 7 . Payload Format Parameters....................................48 102 7.1 Media Type Registration...................................48 103 7.2 SDP Parameters............................................71 104 7.2.1 Mapping of Payload Type Parameters to SDP............71 105 7.2.2 Usage with SDP Offer/Answer Model....................72 106 7.2.3 Usage in Declarative Session Descriptions............80 107 7.2.4 Parameter Sets Considerations........................81 108 7.2.5 Dependency Signaling in Multi-Stream Transmission....82 109 8 . Use with Feedback Messages...................................82 110 8.1 Picture Loss Indication (PLI).............................83 111 8.2 Slice Loss Indication.....................................83 112 8.3 Use of HEVC with the RPSI Feedback Message................84 113 8.4 Full Intra Request (FIR)..................................85 114 9 . Security Considerations......................................85 115 10 . Congestion Control..........................................87 116 11 . IANA Consideration..........................................88 117 12 . Acknowledgements............................................88 118 13 . References..................................................88 119 13.1 Normative References.....................................88 120 13.2 Informative References...................................90 121 14 . Authors' Addresses..........................................91 123 1. Introduction 125 1.1. Overview of the HEVC Codec 127 High Efficiency Video Coding [HEVC], formally known as ITU-T 128 Recommendation H.265 and ISO/IEC International Standard 23008-2 was 129 ratified by ITU-T in April 2013 and reportedly provides significant 130 coding efficiency gains over H.264 [H.264]. 132 As both H.264 [H.264] and its RTP payload format [RFC6184] are 133 widely deployed and generally known in the relevant implementer 134 communities, frequently only the differences between those two 135 specifications are highlighted in non-normative, explanatory parts 136 of this memo. Basic familiarity with both specifications is assumed 137 for those parts. However, the normative parts of this memo do not 138 require study of H.264 or its RTP payload format. 140 H.264 and HEVC share a similar hybrid video codec design. 141 Conceptually, both technologies include a video coding layer (VCL), 142 which is often used to refer to the coding-tool features, and a 143 network abstraction layer (NAL), which is often used to refer to the 144 systems and transport interface aspects of the codecs. 146 1.1.1 Coding-Tool Features 148 Similarly to earlier hybrid-video-coding-based standards, including 149 H.264, the following basic video coding design is employed by HEVC. 150 A prediction signal is first formed either by intra or motion 151 compensated prediction, and the residual (the difference between the 152 original and the prediction) is then coded. The gains in coding 153 efficiency are achieved by redesigning and improving almost all 154 parts of the codec over earlier designs. In addition, HEVC includes 155 several tools to make the implementation on parallel architectures 156 easier. Below is a summary of HEVC coding-tool features. 158 Quad-tree block and transform structure 160 One of the major tools that contribute significantly to the coding 161 efficiency of HEVC is the usage of flexible coding blocks and 162 transforms, which are defined in a hierarchical quad-tree manner. 163 Unlike H.264, where the basic coding block is a macroblock of fixed 164 size 16x16, HEVC defines a Coding Tree Unit (CTU) of a maximum size 165 of 64x64. Each CTU can be divided into smaller units in a 166 hierarchical quad-tree manner and can represent smaller blocks down 167 to size 4x4. Similarly, the transforms used in HEVC can have 168 different sizes, starting from 4x4 and going up to 32x32. Utilizing 169 large blocks and transforms contribute to the major gain of HEVC, 170 especially at high resolutions. 172 Entropy coding 174 HEVC uses a single entropy coding engine, which is based on Context 175 Adaptive Binary Arithmetic Coding (CABAC), whereas H.264 uses two 176 distinct entropy coding engines. CABAC in HEVC shares many 177 similarities with CABAC of H.264, but contains several improvements. 178 Those include improvements in coding efficiency and lowered 179 implementation complexity, especially for parallel architectures. 181 In-loop filtering 183 H.264 includes an in-loop adaptive deblocking filter, where the 184 blocking artifacts around the transform edges in the reconstructed 185 picture are smoothed to improve the picture quality and compression 186 efficiency. In HEVC, a similar deblocking filter is employed but 187 with somewhat lower complexity. In addition, pictures undergo a 188 subsequent filtering operation called Sample Adaptive Offset (SAO), 189 which is a new design element in HEVC. SAO basically adds a pixel- 190 level offset in an adaptive manner and usually acts as a de-ringing 191 filter. It is observed that SAO improves the picture quality, 192 especially around sharp edges contributing substantially to visual 193 quality improvements of HEVC. 195 Motion prediction and coding 197 There have been a number of improvements in this area that are 198 summarized as follows. The first category is motion merge and 199 advanced motion vector prediction (AMVP) modes. The motion 200 information of a prediction block can be inferred from the spatially 201 or temporally neighboring blocks. This is similar to the DIRECT 202 mode in H.264 but includes new aspects to incorporate the flexible 203 quad-tree structure and methods to improve the parallel 204 implementations. In addition, the motion vector predictor can be 205 signaled for improved efficiency. The second category is high- 206 precision interpolation. The interpolation filter length is 207 increased to 8-tap from 6-tap, which improves the coding efficiency 208 but also comes with increased complexity. In addition, the 209 interpolation filter is defined with higher precision without any 210 intermediate rounding operations to further improve the coding 211 efficiency. 213 Intra prediction and intra coding 215 Compared to 8 intra prediction modes in H.264, HEVC supports angular 216 intra prediction with 33 directions. This increased flexibility 217 improves both objective coding efficiency and visual quality as the 218 edges can be better predicted and ringing artifacts around the edges 219 can be reduced. In addition, the reference samples are adaptively 220 smoothed based on the prediction direction. To avoid contouring 221 artifacts a new interpolative prediction generation is included to 222 improve the visual quality. Furthermore, discrete sine transform 223 (DST) is utilized instead of traditional discrete cosine transform 224 (DCT) for 4x4 intra transform blocks. 226 Other coding-tool features 228 HEVC includes some tools for lossless coding and efficient screen 229 content coding, such as skipping the transform for certain blocks. 230 These tools are particularly useful for example when streaming the 231 user-interface of a mobile device to a large display. 233 1.1.2 Systems and Transport Interfaces 235 HEVC inherited the basic systems and transport interfaces designs, 236 such as the NAL-unit-based syntax structure, the hierarchical syntax 237 and data unit structure from sequence-level parameter sets, multi- 238 picture-level or picture-level parameter sets, slice-level header 239 parameters, lower-level parameters, the supplemental enhancement 240 information (SEI) message mechanism, the hypothetical reference 241 decoder (HRD) based video buffering model, and so on. In the 242 following, a list of differences in these aspects compared to H.264 243 is summarized. 245 Video parameter set 247 A new type of parameter set, called video parameter set (VPS), was 248 introduced. For the first (2013) version of [HEVC], the video 249 parameter set NAL unit is required to be available prior to its 250 activation, while the information contained in the video parameter 251 set is not necessary for operation of the decoding process. For 252 future HEVC extensions, such as the 3D or scalable extensions, the 253 video parameter set is expected to include information necessary for 254 operation of the decoding process, e.g. decoding dependency or 255 information for reference picture set construction of enhancement 256 layers. The VPS provides a "big picture" of a bitstream, including 257 what types of operation points are provided, the profile, tier, and 258 level of the operation points, and some other high-level properties 259 of the bitstream that can be used as the basis for session 260 negotiation and content selection, etc. (see section 7.1). 262 Profile, tier and level 264 The profile, tier and level syntax structure that can be included in 265 both VPS and sequence parameter set (SPS) includes 12 bytes of data 266 to describe the entire bitstream (including all temporally scalable 267 layers, which are referred to as sub-layers in the HEVC 268 specification), and can optionally include more profile, tier and 269 level information pertaining to individual temporally scalable 270 layers. The profile indicator indicates the "best viewed as" 271 profile when the bitstream conforms to multiple profiles, similar to 272 the major brand concept in the ISO base media file format (ISOBMFF) 273 [ISOBMFF] and file formats derived based on ISOBMFF, such as the 274 3GPP file format [3GP]. The profile, tier and level syntax 275 structure also includes the indications of whether the bitstream is 276 free of frame-packed content, whether the bitstream is free of 277 interlaced source content and free of field pictures, i.e. contains 278 only frame pictures of progressive source, such that clients/players 279 with no support of post-processing functionalities for handling of 280 frame-packed or interlaced source content or field pictures can 281 reject those bitstreams. 283 Bitstream and elementary stream 285 HEVC includes a definition of an elementary stream, which is new 286 compared to H.264. An elementary stream consists of a sequence of 287 one or more bitstreams. An elementary stream that consists of two 288 or more bitstreams has typically been formed by splicing together 289 two or more bitstreams (or parts thereof). When an elementary 290 stream contains more than one bitstream, the last NAL unit of the 291 last access unit of a bitstream (except the last bitstream in the 292 elementary stream) must contain an end of bitstream NAL unit and the 293 first access unit of the subsequent bitstream must be an intra 294 random access point (IRAP) access unit. This IRAP access unit may 295 be a clean random access (CRA), broken link access (BLA), or 296 instantaneous decoding refresh (IDR) access unit. 298 Random access support 300 HEVC includes signaling in NAL unit header, through NAL unit types, 301 of IRAP pictures beyond IDR pictures. Three types of IRAP pictures, 302 namely IDR, CRA and BLA pictures are supported, wherein IDR pictures 303 are conventionally referred to as closed group-of-pictures (closed- 304 GOP) random access points, and CRA and BLA pictures are those 305 conventionally referred to as open-GOP random access points. BLA 306 pictures usually originate from splicing of two bitstreams or part 307 thereof at a CRA picture, e.g. during stream switching. To enable 308 better systems usage of IRAP pictures, altogether six different NAL 309 units are defined to signal the properties of the IRAP pictures, 310 which can be used to better match the stream access point (SAP) 311 types as defined in the ISOBMFF [ISOBMFF], which are utilized for 312 random access support in both 3GP-DASH [3GPDASH] and MPEG DASH 313 [MPEGDASH]. Pictures following an IRAP picture in decoding order 314 and preceding the IRAP picture in output order are referred to as 315 leading pictures associated with the IRAP picture. There are two 316 types of leading pictures, namely random access decodable leading 317 (RADL) pictures and random access skipped leading (RASL) pictures. 318 RADL pictures are decodable when the decoding started at the 319 associated IRAP picture, and RASL pictures are not decodable when 320 the decoding started at the associated IRAP picture and are usually 321 discarded. HEVC provides mechanisms to enable the specification of 322 conformance of bitstreams with RASL pictures being discarded, thus 323 to provide a standard-compliant way to enable systems components to 324 discard RASL pictures when needed. 326 Temporal scalability support 328 HEVC includes an improved support of temporal scalability, by 329 inclusion of the signaling of TemporalId in the NAL unit header, the 330 restriction that pictures of a particular temporal sub-layer cannot 331 be used for inter prediction reference by pictures of a lower 332 temporal sub-layer, the sub-bitstream extraction process, and the 333 requirement that each sub-bitstream extraction output be a 334 conforming bitstream. Media-aware network elements (MANEs) can 335 utilize the TemporalId in the NAL unit header for stream adaptation 336 purposes based on temporal scalability. 338 Temporal sub-layer switching support 340 HEVC specifies, through NAL unit types present in the NAL unit 341 header, the signaling of temporal sub-layer access (TSA) and 342 stepwise temporal sub-layer access (STSA). A TSA picture and 343 pictures following the TSA picture in decoding order do not use 344 pictures prior to the TSA picture in decoding order with TemporalId 345 greater than or equal to that of the TSA picture for inter 346 prediction reference. A TSA picture enables up-switching, at the 347 TSA picture, to the sub-layer containing the TSA picture or any 348 higher sub-layer, from the immediately lower sub-layer. An STSA 349 picture does not use pictures with the same TemporalId as the STSA 350 picture for inter prediction reference. Pictures following an STSA 351 picture in decoding order with the same TemporalId as the STSA 352 picture do not use pictures prior to the STSA picture in decoding 353 order with the same TemporalId as the STSA picture for inter 354 prediction reference. An STSA picture enables up-switching, at the 355 STSA picture, to the sub-layer containing the STSA picture, from the 356 immediately lower sub-layer. 358 Sub-layer reference or non-reference pictures 360 The concept and signaling of reference/non-reference pictures in 361 HEVC are different from H.264. In H.264, if a picture may be used 362 by any other picture for inter prediction reference, it is a 363 reference picture; otherwise it is a non-reference picture, and this 364 is signaled by two bits in the NAL unit header. In HEVC, a picture 365 is called a reference picture only when it is marked as "used for 366 reference". In addition, the concept of sub-layer reference picture 367 was introduced. If a picture may be used by another other picture 368 with the same TemporalId for inter prediction reference, it is a 369 sub-layer reference picture; otherwise it is a sub-layer non- 370 reference picture. Whether a picture is a sub-layer reference 371 picture or sub-layer non-reference picture is signaled through NAL 372 unit type values. 374 Extensibility 376 Besides the TemporalId in the NAL unit header, HEVC also includes 377 the signaling of a six-bit layer ID in the NAL unit header, which 378 must be equal to 0 for a single-layer bitstream. Extension 379 mechanisms have been included in VPS, SPS, PPS, SEI NAL unit, slice 380 headers, and so on. All these extension mechanisms enable future 381 extensions in a backward compatible manner, such that bitstreams 382 encoded according to potential future HEVC extensions can be fed to 383 then-legacy decoders (e.g. HEVC version 1 decoders) and the then- 384 legacy decoders can decode and output the base layer bitstream. 386 Bitstream extraction 388 HEVC includes a bitstream extraction process as an integral part of 389 the overall decoding process, as well as specification of the use of 390 the bitstream extraction process in description of bitstream 391 conformance tests as part of the hypothetical reference decoder 392 (HRD) specification. 394 Reference picture management 396 The reference picture management of HEVC, including reference 397 picture marking and removal from the decoded picture buffer (DPB) as 398 well as reference picture list construction (RPLC), differs from 399 that of H.264. Instead of the sliding window plus adaptive memory 400 management control operation (MMCO) based reference picture marking 401 mechanism in H.264, HEVC specifies a reference picture set (RPS) 402 based reference picture management and marking mechanism, and the 403 RPLC is consequently based on the RPS mechanism. A reference 404 picture set consists of a set of reference pictures associated with 405 a picture, consisting of all reference pictures that are prior to 406 the associated picture in decoding order, that may be used for inter 407 prediction of the associated picture or any picture following the 408 associated picture in decoding order. The reference picture set 409 consists of five lists of reference pictures; RefPicSetStCurrBefore, 410 RefPicSetStCurrAfter, RefPicSetStFoll, RefPicSetLtCurr and 411 RefPicSetLtFoll. RefPicSetStCurrBefore, RefPicSetStCurrAfter and 412 RefPicSetLtCurr contain all reference pictures that may be used in 413 inter prediction of the current picture and that may be used in 414 inter prediction of one or more of the pictures following the 415 current picture in decoding order. RefPicSetStFoll and 416 RefPicSetLtFoll consist of all reference pictures that are not used 417 in inter prediction of the current picture but may be used in inter 418 prediction of one or more of the pictures following the current 419 picture in decoding order. RPS provides an "intra-coded" signaling 420 of the DPB status, instead of an "inter-coded" signaling, mainly for 421 improved error resilience. The RPLC process in HEVC is based on the 422 RPS, by signaling an index to an RPS subset for each reference 423 index. The RPLC process has been simplified compared to that in 424 H.264, by removal of the reference picture list modification (also 425 referred to as reference picture list reordering) process. 427 Ultra low delay support 429 HEVC specifies a sub-picture-level HRD operation, for support of the 430 so-called ultra-low delay. The mechanism specifies a standard- 431 compliant way to enable delay reduction below one picture interval. 432 Sub-picture-level coded picture buffer (CPB) and DPB parameters may 433 be signaled, and utilization of these information for the derivation 434 of CPB timing (wherein the CPB removal time corresponds to decoding 435 time) and DPB output timing (display time) is specified. Decoders 436 are allowed to operate the HRD at the conventional access-unit- 437 level, even when the sub-picture-level HRD parameters are present. 439 New SEI messages 441 HEVC inherits many H.264 SEI messages with changes in syntax and/or 442 semantics making them applicable to HEVC. Additionally, there are a 443 few new SEI messages reviewed briefly in the following paragraphs. 445 The display orientation SEI message informs the decoder of a 446 transformation that is recommended to be applied to the cropped 447 decoded picture prior to display, such that the pictures can be 448 properly displayed, e.g. in an upside-up manner. 450 The structure of pictures SEI message provides information on the 451 NAL unit types, picture order count values, and prediction 452 dependencies of a sequence of pictures. The SEI message can be used 453 for example for concluding what impact a lost picture has on other 454 pictures. 456 The decoded picture hash SEI message provides a checksum derived 457 from the sample values of a decoded picture. It can be used for 458 detecting whether a picture was correctly received and decoded. 460 The active parameter sets SEI message includes the IDs of the active 461 video parameter set and the active sequence parameter set and can be 462 used to activate VPSs and SPSs. In addition, the SEI message 463 includes the following indications: 1) An indication of whether 464 "full random accessibility" is supported (when supported, all 465 parameter sets needed for decoding of the remaining of the bitstream 466 when random accessing from the beginning of the current coded video 467 sequence by completely discarding all access units earlier in 468 decoding order are present in the remaining bitstream and all coded 469 pictures in the remaining bitstream can be correctly decoded); 2) An 470 indication of whether there is no parameter set within the current 471 coded video sequence that updates another parameter set of the same 472 type preceding in decoding order. An update of a parameter set 473 refers to the use of the same parameter set ID but with some other 474 parameters changed. If this property is true for all coded video 475 sequences in the bitstream, then all parameter sets can be sent out- 476 of-band before session start. 478 The decoding unit information SEI message provides coded picture 479 buffer removal delay information for a decoding unit. The message 480 can be used in very-low-delay buffering operations. 482 The region refresh information SEI message can be used together with 483 the recovery point SEI message (present in both H.264 and HEVC) for 484 improved support of gradual decoding refresh (GDR). This supports 485 random access from inter-coded pictures, wherein complete pictures 486 can be correctly decoded or recovered after an indicated number of 487 pictures in output/display order. 489 1.1.3 Parallel Processing Support 491 The reportedly significantly higher encoding computational demand of 492 HEVC over H.264, in conjunction with the ever increasing video 493 resolution (both spatially and temporally) required by the market, 494 led to the adoption of VCL coding tools specifically targeted to 495 allow for parallelization on the sub-picture level. That is, 496 parallelization occurs, at the minimum, at the granularity of an 497 integer number of CTUs. The targets for this type of high-level 498 parallelization are multicore CPUs and DSPs as well as 499 multiprocessor systems. In a system design, to be useful, these 500 tools require signaling support, which is provided in Section 7 of 501 this memo. This section provides a brief overview of the tools 502 available in [HEVC]. 504 Many of the tools incorporated in HEVC were designed keeping in mind 505 the potential parallel implementations in multi-core/multi-processor 506 architectures. Specifically, for parallelization, four picture 507 partition strategies are available. 509 Slices are segments of the bitstream that can be reconstructed 510 independently from other slices within the same picture (though 511 there may still be interdependencies through loop filtering 512 operations). Slices are the only tool that can be used for 513 parallelization that is also available, in virtually identical form, 514 in H.264. Slices based parallelization does not require much inter- 515 processor or inter-core communication (except for inter-processor or 516 inter-core data sharing for motion compensation when decoding a 517 predictively coded picture, which is typically much heavier than 518 inter-processor or inter-core data sharing due to in-picture 519 prediction), as slices are designed to be independently decodable. 520 However, for the same reason, slices can require some coding 521 overhead. Further, slices (in contrast to some of the other tools 522 mentioned below) also serve as the key mechanism for bitstream 523 partitioning to match Maximum Transfer Unit (MTU) size requirements, 524 due to the in-picture independence of slices and the fact that each 525 regular slice is encapsulated in its own NAL unit. In many cases, 526 the goal of parallelization and the goal of MTU size matching can 527 place contradicting demands to the slice layout in a picture. The 528 realization of this situation led to the development of the more 529 advanced tools mentioned below. 531 Dependent slice segments allow for fragmentation of a coded slice 532 into fragments at CTU boundaries without breaking any in-picture 533 prediction mechanism. They are complementary to the fragmentation 534 mechanism described in this memo in that they need the cooperation 535 of the encoder. As a dependent slice segment necessarily contains 536 an integer number of CTUs, a decoder using multiple cores operating 537 on CTUs can process a dependent slice segment without communicating 538 parts of the slice segment's bitstream to other cores. 539 Fragmentation, as specified in this memo, in contrast, does not 540 guarantee that a fragment contains an integer number of CTUs. 542 In wavefront parallel processing (WPP), the picture is partitioned 543 into rows of CTUs. Entropy decoding and prediction are allowed to 544 use data from CTUs in other partitions. Parallel processing is 545 possible through parallel decoding of CTU rows, where the start of 546 the decoding of a row is delayed by two CTUs, so to ensure that data 547 related to a CTU above and to the right of the subject CTU is 548 available before the subject CTU is being decoded. Using this 549 staggered start (which appears like a wavefront when represented 550 graphically), parallelization is possible with up to as many 551 processors/cores as the picture contains CTU rows. 553 Because in-picture prediction between neighboring CTU rows within a 554 picture is allowed, the required inter-processor/inter-core 555 communication to enable in-picture prediction can be substantial. 556 The WPP partitioning does not result in the creation of more NAL 557 units compared to when it is not applied, thus WPP cannot be used 558 for MTU size matching, though slices can be used in combination for 559 that purpose. 561 Tiles define horizontal and vertical boundaries that partition a 562 picture into tile columns and rows. The scan order of CTUs is 563 changed to be local within a tile (in the order of a CTU raster scan 564 of a tile), before decoding the top-left CTU of the next tile in the 565 order of tile raster scan of a picture. Similar to slices, tiles 566 break in-picture prediction dependencies (including entropy decoding 567 dependencies). However, they do not need to be included into 568 individual NAL units (same as WPP in this regard), hence tiles 569 cannot be used for MTU size matching, though slices can be used in 570 combination for that purpose. Each tile can be processed by one 571 processor/core, and the inter-processor/inter-core communication 572 required for in-picture prediction between processing units decoding 573 neighboring tiles is limited to conveying the shared slice header in 574 cases a slice is spanning more than one tile, and loop filtering 575 related sharing of reconstructed samples and metadata. Insofar, 576 tiles are less demanding in terms of inter-processor communication 577 bandwidth compared to WPP due to the in-picture independence between 578 two neighboring partitions. 580 1.1.4 NAL Unit Header 582 HEVC maintains the NAL unit concept of H.264 with modifications. 583 HEVC uses a two-byte NAL unit header, as shown in Figure 1. The 584 payload of a NAL unit refers to the NAL unit excluding the NAL unit 585 header. 587 +---------------+---------------+ 588 |0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7| 589 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 590 |F| Type | LayerId | TID | 591 +-------------+-----------------+ 593 Figure 1 The structure of HEVC NAL unit header 595 The semantics of the fields in the NAL unit header are as specified 596 in [HEVC] and described briefly below for convenience. In addition 597 to the name and size of each field, the corresponding syntax element 598 name in [HEVC] is also provided. 600 F: 1 bit 601 forbidden_zero_bit. MUST be zero. HEVC declares a value of 1 as 602 a syntax violation. Note that the inclusion of this bit in the 603 NAL unit header is to enable transport of HEVC video over MPEG-2 604 transport systems (avoidance of start code emulations) [MPEG2S]. 606 Type: 6 bits 607 nal_unit_type. This field specifies the NAL unit type as defined 608 in Table 7-1 of [HEVC]. If the most significant bit of this 609 field of a NAL unit is equal to 0 (i.e. the value of this field 610 is less than 32), the NAL unit is a VCL NAL unit. Otherwise, the 611 NAL unit is a non-VCL NAL unit. For a reference of all currently 612 defined NAL unit types and their semantics, please refer to 613 Section 7.4.1 in [HEVC]. 615 LayerId: 6 bits 616 nuh_layer_id. MUST be equal to zero. It is anticipated that in 617 future scalable or 3D video coding extensions of this 618 specification, this syntax element will be used to identify 619 additional layers that may be present in the coded video 620 sequence, wherein a layer may be, e.g. a spatial scalable layer, 621 a quality scalable layer, a texture view, or a depth view. 623 TID: 3 bits 624 nuh_temporal_id_plus1. This field specifies the temporal 625 identifier of the NAL unit plus 1. The value of TemporalId is 626 equal to TID minus 1. A TID value of 0 is illegal to ensure that 627 there is at least one bit in the NAL unit header equal to 1, so 628 to enable independent considerations of start code emulations in 629 the NAL unit header and in the NAL unit payload data. 631 1.2. Overview of the Payload Format 633 This payload format defines the following processes required for 634 transport of HEVC coded data over RTP [RFC3550]: 636 o Usage of RTP header with this payload format 638 o Packetization of HEVC coded NAL units into RTP packets using three 639 types of payload structures, namely single NAL unit packet, 640 aggregation packet, and fragment unit 642 o Transmission of HEVC NAL units of the same bitstream within a 643 single RTP stream or multiple RTP streams within one or more RTP 644 sessions, where within an RTP stream transmission of NAL units may 645 be either non-interleaved (i.e. the transmission order of NAL 646 units is the same as their decoding order) or interleaved (i.e. 648 the transmission order of NAL units is different from their 649 decoding order) 651 o Media type parameters to be used with the Session Description 652 Protocol (SDP) [RFC4566] 654 o A payload header extension mechanism and data structures for 655 enhanced support of temporal scalability based on that extension 656 mechanism. 658 2. Conventions 660 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 661 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 662 document are to be interpreted as described in BCP 14, RFC 2119 663 [RFC2119]. 665 In this document, these key words will appear with that 666 interpretation only when in ALL CAPS. Lower case uses of these 667 words are not to be interpreted as carrying the RFC 2119 668 significance. 670 This specification uses the notion of setting and clearing a bit 671 when bit fields are handled. Setting a bit is the same as assigning 672 that bit the value of 1 (On). Clearing a bit is the same as 673 assigning that bit the value of 0 (Off). 675 3. Definitions and Abbreviations 677 3.1 Definitions 679 This document uses the terms and definitions of [HEVC]. Section 680 3.1.1 lists relevant definitions copied from [HEVC] for convenience. 681 Section 3.1.2 provides definitions specific to this memo. 683 3.1.1 Definitions from the HEVC Specification 685 access unit: A set of NAL units that are associated with each other 686 according to a specified classification rule, are consecutive in 687 decoding order, and contain exactly one coded picture. 689 BLA access unit: An access unit in which the coded picture is a BLA 690 picture. 692 BLA picture: An IRAP picture for which each VCL NAL unit has 693 nal_unit_type equal to BLA_W_LP, BLA_W_RADL, or BLA_N_LP. 695 coded video sequence: A sequence of access units that consists, in 696 decoding order, of an IRAP access unit with NoRaslOutputFlag equal 697 to 1, followed by zero or more access units that are not IRAP access 698 units with NoRaslOutputFlag equal to 1, including all subsequent 699 access units up to but not including any subsequent access unit that 700 is an IRAP access unit with NoRaslOutputFlag equal to 1. 702 Informative note: An IRAP access unit may be an IDR access unit, 703 a BLA access unit, or a CRA access unit. The value of 704 NoRaslOutputFlag is equal to 1 for each IDR access unit, each BLA 705 access unit, and each CRA access unit that is the first access 706 unit in the bitstream in decoding order, is the first access unit 707 that follows an end of sequence NAL unit in decoding order, or 708 has HandleCraAsBlaFlag equal to 1. 710 CRA access unit: An access unit in which the coded picture is a CRA 711 picture. 713 CRA picture: A RAP picture for which each VCL NAL unit has 714 nal_unit_type equal to CRA_NUT. 716 IDR access unit: An access unit in which the coded picture is an IDR 717 picture. 719 IDR picture: A RAP picture for which each VCL NAL unit has 720 nal_unit_type equal to IDR_W_RADL or IDR_N_LP. 722 IRAP access unit: An access unit in which the coded picture is an 723 IRAP picture. 725 IRAP picture: A coded picture for which each VCL NAL unit has 726 nal_unit_type in the range of BLA_W_LP (16) to RSV_IRAP_VCL23 (23), 727 inclusive. 729 layer: A set of VCL NAL units that all have a particular value of 730 nuh_layer_id and the associated non-VCL NAL units, or one of a set 731 of syntactical structures having a hierarchical relationship. 733 operation point: bitstream created from another bitstream by 734 operation of the sub-bitstream extraction process with the another 735 bitstream, a target highest TemporalId, and a target layer 736 identifier list as inputs. 738 random access: The act of starting the decoding process for a 739 bitstream at a point other than the beginning of the bitstream. 741 sub-layer: A temporal scalable layer of a temporal scalable 742 bitstream consisting of VCL NAL units with a particular value of the 743 TemporalId variable, and the associated non-VCL NAL units. 745 tile: A rectangular region of coding tree blocks within a particular 746 tile column and a particular tile row in a picture. 748 tile column: A rectangular region of coding tree blocks having a 749 height equal to the height of the picture and a width specified by 750 syntax elements in the picture parameter set. 752 tile row: A rectangular region of coding tree blocks having a height 753 specified by syntax elements in the picture parameter set and a 754 width equal to the width of the picture. 756 3.1.2 Definitions Specific to This Memo 758 dependent RTP stream: An RTP stream on which another RTP stream 759 depends. All RTP streams in an MST except for the highest RTP 760 stream are all dependent RTP streams. 762 highest RTP stream: The packet stream on which no other RTP stream 763 depends. The RTP stream in an SST is the highest RTP stream. 765 media aware network element (MANE): A network element, such as a 766 middlebox, selective forwarding unit, or application layer gateway 767 that is capable of parsing certain aspects of the RTP payload 768 headers or the RTP payload and reacting to their contents. 770 Informative note: The concept of a MANE goes beyond normal 771 routers or gateways in that a MANE has to be aware of the 772 signaling (e.g. to learn about the payload type mappings of the 773 media streams), and in that it has to be trusted when working 774 with SRTP. The advantage of using MANEs is that they allow 775 packets to be dropped according to the needs of the media coding. 776 For example, if a MANE has to drop packets due to congestion on a 777 certain link, it can identify and remove those packets whose 778 elimination produces the least adverse effect on the user 779 experience. After dropping packets, MANEs must rewrite RTCP 780 packets to match the changes to the RTP stream as specified in 781 Section 7 of [RFC3550]. 783 multi-stream transmission (MST): Transmission of an HEVC bitstream 784 using more than one RTP stream. 786 NAL unit decoding order: A NAL unit order that conforms to the 787 constraints on NAL unit order given in Section 7.4.2.4 in [HEVC]. 789 NAL-unit-like structure: A data structure that is similar to NAL 790 units in the sense that it also has a NAL unit header and a payload, 791 with a difference that the payload does not follow the start code 792 emulation prevention mechanism required for the NAL unit syntax as 793 specified in Section 7.3.1.1 of [HEVC]. Examples NAL-unit-like 794 structures defined in this memo are packet payloads of AP, PACI, and 795 FU packets. 797 NALU-time: The value that the RTP timestamp would have if the NAL 798 unit would be transported in its own RTP packet. 800 packet stream: See [I-D.ietf-avtext-rtp-grouping-taxonomy]. Within 801 the scope of this memo, one RTP stream is utilized to transport one 802 or more temporal sub-layers. 804 single-stream transmission (SST): Transmission of an HEVC bitstream 805 using only one RTP stream. 807 transmission order: The order of packets in ascending RTP sequence 808 number order (in modulo arithmetic). Within an aggregation packet, 809 the NAL unit transmission order is the same as the order of 810 appearance of NAL units in the packet. 812 3.2 Abbreviations 814 AP Aggregation Packet 816 BLA Broken Link Access 818 CRA Clean Random Access 820 CTB Coding Tree Block 822 CTU Coding Tree Unit 824 CVS Coded Video Sequence 826 FU Fragmentation Unit 828 GDR Gradual Decoding Refresh 830 HRD Hypothetical Reference Decoder 832 IDR Instantaneous Decoding Refresh 834 IRAP Intra Random Access Point 836 MANE Media Aware Network Element 838 MST Multi-Stream Transmission 840 MTU Maximum Transfer Unit 842 NAL Network Abstraction Layer 844 NALU Network Abstraction Layer Unit 846 PACI PAyload Content Information 848 PHES Payload Header Extension Structure 850 PPS Picture Parameter Set 852 RADL Random Access Decodable Leading (Picture) 854 RASL Random Access Skipped Leading (Picture) 855 RPS Reference Picture Set 857 SEI Supplemental Enhancement Information 859 SPS Sequence Parameter Set 861 SST Single-Stream Transmission 863 STSA Step-wise Temporal Sub-layer Access 865 TSA Temporal Sub-layer Access 867 TCSI Temporal Scalability Control Information 869 VCL Video Coding Layer 871 VPS Video Parameter Set 873 4. RTP Payload Format 875 4.1 RTP Header Usage 877 The format of the RTP header is specified in [RFC3550] and reprinted 878 in Figure 2 for convenience. This payload format uses the fields of 879 the header in a manner consistent with that specification. 881 The RTP payload (and the settings for some RTP header bits) for 882 aggregation packets and fragmentation units are specified in 883 Sections 4.7 and 4.8, respectively. 885 0 1 2 3 886 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 1 887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 888 |V=2|P|X| CC |M| PT | sequence number | 889 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 890 | timestamp | 891 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 892 | synchronization source (SSRC) identifier | 893 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 894 | contributing source (CSRC) identifiers | 895 | .... | 896 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 898 Figure 2 RTP header according to [RFC3550] 900 The RTP header information to be set according to this RTP payload 901 format is set as follows: 903 Marker bit (M): 1 bit 905 Set for the last packet, carried in the current RTP stream, of 906 the access unit, in line with the normal use of the M bit in 907 video formats, to allow an efficient playout buffer handling. 908 When MST is in use, if an access unit appears in multiple RTP 909 streams, the marker bit is set on each RTP stream's last packet 910 of the access unit. 912 Informative note: The content of a NAL unit does not tell 913 whether or not the NAL unit is the last NAL unit, in decoding 914 order, of an access unit. An RTP sender implementation may 915 obtain this information from the video encoder. If, however, 916 the implementation cannot obtain this information directly 917 from the encoder, e.g. when the bitstream was pre-encoded, and 918 also there is no timestamp allocated for each NAL unit, then 919 the sender implementation can inspect subsequent NAL units in 920 decoding order to determine whether or not the NAL unit is the 921 last NAL unit of an access unit as follows. A NAL unit naluX 922 is the last NAL unit of an access unit if it is the last NAL 923 unit of the bitstream or the next VCL NAL unit naluY in 924 decoding order has the high-order bit of the first byte after 925 its NAL unit header equal to 1, and all NAL units between 926 naluX and naluY, when present, have nal_unit_type in the range 927 of 32 to 35, inclusive, equal to 39, or in the ranges of 41 to 928 44, inclusive, or 48 to 55, inclusive. 930 Payload type (PT): 7 bits 932 The assignment of an RTP payload type for this new packet format 933 is outside the scope of this document and will not be specified 934 here. The assignment of a payload type has to be performed 935 either through the profile used or in a dynamic way. 937 Informative note: It is not required to use different payload 938 type values for different RTP streams in MST. 940 Sequence number (SN): 16 bits 942 Set and used in accordance with RFC 3550. 944 Timestamp: 32 bits 946 The RTP timestamp is set to the sampling timestamp of the 947 content. A 90 kHz clock rate MUST be used. 949 If the NAL unit has no timing properties of its own (e.g. 950 parameter set and SEI NAL units), the RTP timestamp MUST be set 951 to the RTP timestamp of the coded picture of the access unit in 952 which the NAL unit (according to Section 7.4.2.4.4 of [HEVC]) is 953 included. 955 Receivers MUST use the RTP timestamp for the display process, 956 even when the bitstream contains picture timing SEI messages or 957 decoding unit information SEI messages as specified in [HEVC]. 958 However, this does not mean that picture timing SEI messages in 959 the bitstream should be discarded, as picture timing SEI messages 960 may contain frame-field information that is important in 961 appropriately rendering interlaced video. 963 Synchronization source (SSRC): 32-bits 965 Used to identify the source of the RTP packets. In SST, by 966 definition a single SSRC is used for all parts of a single 967 bitstream. In MST, each SSRC is used for an RTP stream 968 containing a subset of the sub-layers for a single (temporally 969 scalable) bitstream. A receiver is required to correctly 970 associate the set of SSRCs that are included parts of the same 971 bitstream. 973 Informative note: The term "bitstream" in this document is 974 equivalent to the term "encoded stream" in [I-D.ietf-avtext- 975 rtp-grouping-taxonomy]. 977 4.2 Payload Header Usage 979 The TID value indicates (among other things) the relative importance 980 of an RTP packet, for example because NAL units belonging to higher 981 temporal sub-layers are not used for the decoding of lower temporal 982 sub-layers. A lower value of TID indicates a higher importance. 983 More important NAL units MAY be better protected against 984 transmission losses than less important NAL units. 986 4.3 Payload Structures 988 The first two bytes of the payload of an RTP packet are referred to 989 as the payload header. The payload header consists of the same 990 fields (F, Type, LayerId, and TID) as the NAL unit header as shown 991 in section 1.1.4, irrespective of the type of the payload structure. 993 Four different types of RTP packet payload structures are specified. 994 A receiver can identify the type of an RTP packet payload through 995 the Type field in the payload header. 997 The four different payload structures are as follows: 999 o Single NAL unit packet: Contains a single NAL unit in the 1000 payload, and the NAL unit header of the NAL unit also serves as 1001 the payload header. This payload structure is specified in 1002 section 4.6. 1004 o Aggregation packet (AP): Contains more than one NAL unit within 1005 one access unit. This payload structure is specified in 1006 section 4.7. 1008 o Fragmentation unit (FU): Contains a subset of a single NAL unit. 1009 This payload structure is specified in section 4.8. 1011 o PACI carrying RTP packet: Contains a payload header (that differs 1012 from other payload headers for efficiency), a Payload Header 1013 Extension Structure (PHES), and a PACI payload. This payload 1014 structure is specified in section 4.9. 1016 4.4 Transmission Modes 1018 This memo enables transmission of an HEVC bitstream over a single 1019 packet stream or multiple RTP streams. The concept and working 1020 principle is inherited from the design of what was called single and 1021 multiple session transmission in [RFC6190] and follows a similar 1022 design. If only one RTP stream is used for transmission of the HEVC 1023 bitstream, the transmission mode is referred to as single-stream 1024 transmission (SST); otherwise (more than one RTP stream is used for 1025 transmission of the HEVC bitstream), the transmission mode is 1026 referred to as multi-stream transmission (MST). 1028 Dependency of one RTP stream on another RTP stream is typically 1029 indicated as specified in [RFC5583]. When an RTP stream A depends 1030 on another RTP stream B, the RTP stream B is referred to as a 1031 dependent RTP stream of the RTP stream A. 1033 Informative note: An MST may involve one or more RTP sessions. 1034 For example, each RTP stream in an MST may be in its own RTP 1035 session. For another example, a set of multiple RTP streams in 1036 an MST may belong to the same RTP session, e.g. as indicated by 1037 the mechanism specified in [I-D.ietf-avtcore-rtp-multi-stream] or 1038 [I-D.ietf-mmusic-sdp-bundle-negotiation]. 1040 SST SHOULD be used for point-to-point unicast scenarios, while MST 1041 SHOULD be used for point-to-multipoint multicast scenarios where 1042 different receivers require different operation points of the same 1043 HEVC bitstream, to improve bandwidth utilizing efficiency. 1045 Informative note: A multicast may degrade to a unicast after all 1046 but one receivers have left (this is a justification of the first 1047 "SHOULD" instead of "MUST"), and there might be scenarios where 1048 MST is desirable but not possible e.g. when IP multicast is not 1049 deployed in certain network (this is a justification of the 1050 second "SHOULD" instead of "MUST"). 1052 The transmission mode is indicated by the tx-mode media parameter 1053 (see section 7.1). If tx-mode is equal to "SST", SST MUST be used. 1054 Otherwise (tx-mode is equal to "MST"), MST MUST be used. 1056 Receivers MUST support both SST and MST. 1058 4.5 Decoding Order Number 1060 For each NAL unit, the variable AbsDon is derived, representing the 1061 decoding order number that is indicative of the NAL unit decoding 1062 order. 1064 Let NAL unit n be the n-th NAL unit in transmission order within an 1065 RTP stream. 1067 If tx-mode is equal to "SST" and sprop-max-don-diff is equal to 0, 1068 AbsDon[n], the value of AbsDon for NAL unit n, is derived as equal 1069 to n. 1071 Otherwise (tx-mode is equal to "MST" or sprop-max-don-diff is 1072 greater than 0), AbsDon[n] is derived as follows, where DON[n] is 1073 the value of the variable DON for NAL unit n: 1075 o If n is equal to 0 (i.e. NAL unit n is the very first NAL unit in 1076 transmission order), AbsDon[0] is set equal to DON[0]. 1078 o Otherwise (n is greater than 0), the following applies for 1079 derivation of AbsDon[n]: 1081 If DON[n] == DON[n-1], 1082 AbsDon[n] = AbsDon[n-1] 1084 If (DON[n] > DON[n-1] and DON[n] - DON[n-1] < 32768), 1085 AbsDon[n] = AbsDon[n-1] + DON[n] - DON[n-1] 1087 If (DON[n] < DON[n-1] and DON[n-1] - DON[n] >= 32768), 1088 AbsDon[n] = AbsDon[n-1] + 65536 - DON[n-1] + DON[n] 1090 If (DON[n] > DON[n-1] and DON[n] - DON[n-1] >= 32768), 1091 AbsDon[n] = AbsDon[n-1] - (DON[n-1] + 65536 - DON[n]) 1093 If (DON[n] < DON[n-1] and DON[n-1] - DON[n] < 32768), 1094 AbsDon[n] = AbsDon[n-1] - (DON[n-1] - DON[n]) 1096 For any two NAL units m and n, the following applies: 1098 o AbsDon[n] greater than AbsDon[m] indicates that NAL unit n 1099 follows NAL unit m in NAL unit decoding order. 1101 o When AbsDon[n] is equal to AbsDon[m], the NAL unit decoding order 1102 of the two NAL units can be in either order. 1104 o AbsDon[n] less than AbsDon[m] indicates that NAL unit n precedes 1105 NAL unit m in decoding order. 1107 When two consecutive NAL units in the NAL unit decoding order have 1108 different values of AbsDon, the value of AbsDon for the second NAL 1109 unit in decoding order MUST be greater than the value of AbsDon for 1110 the first NAL unit, and the absolute difference between the two 1111 AbsDon values MAY be greater than or equal to 1. 1113 Informative note: There are multiple reasons to allow for the 1114 absolute difference of the values of AbsDon for two consecutive 1115 NAL units in the NAL unit decoding order to be greater than one. 1116 An increment by one is not required, as at the time of 1117 associating values of AbsDon to NAL units, it may not be known 1118 whether all NAL units are to be delivered to the receiver. For 1119 example, a gateway may not forward VCL NAL units of higher sub- 1120 layers or some SEI NAL units when there is congestion in the 1121 network. In another example, the first intra-coded picture of a 1122 pre-encoded clip is transmitted in advance to ensure that it is 1123 readily available in the receiver, and when transmitting the 1124 first intra-coded picture, the originator does not exactly know 1125 how many NAL units will be encoded before the first intra-coded 1126 picture of the pre-encoded clip follows in decoding order. Thus, 1127 the values of AbsDon for the NAL units of the first intra-coded 1128 picture of the pre-encoded clip have to be estimated when they 1129 are transmitted, and gaps in values of AbsDon may occur. Another 1130 example is MST where the AbsDon values must indicate cross-layer 1131 decoding order for NAL units conveyed in all the RTP streams. 1133 4.6 Single NAL Unit Packets 1135 A single NAL unit packet contains exactly one NAL unit, and consists 1136 of a payload header (denoted as PayloadHdr), a conditional 16-bit 1137 DONL field (in network byte order), and the NAL unit payload data 1138 (the NAL unit excluding its NAL unit header) of the contained NAL 1139 unit, as shown in Figure 3. 1141 0 1 2 3 1142 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 1143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1144 | PayloadHdr | DONL (conditional) | 1145 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1146 | | 1147 | NAL unit payload data | 1148 | | 1149 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1150 | :...OPTIONAL RTP padding | 1151 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1153 Figure 3 The structure a single NAL unit packet 1155 The payload header SHOULD be an exact copy of the NAL unit header of 1156 the contained NAL unit. However, the Type (i.e. nal_unit_type) 1157 field MAY be changed, e.g. when it is desirable to handle a CRA 1158 picture to be a BLA picture [JCTVC-J0107]. 1160 The DONL field, when present, specifies the value of the 16 least 1161 significant bits of the decoding order number of the contained NAL 1162 unit. If tx-mode is equal to "MST" or sprop-max-don-diff is greater 1163 than 0, the DONL field MUST be present, and the variable DON for the 1164 contained NAL unit is derived as equal to the value of the DONL 1165 field. Otherwise (tx-mode is equal to "SST" and sprop-max-don-diff 1166 is equal to 0), the DONL field MUST NOT be present. 1168 4.7 Aggregation Packets (APs) 1170 Aggregation packets (APs) are introduced to enable the reduction of 1171 packetization overhead for small NAL units, such as most of the non- 1172 VCL NAL units, which are often only a few octets in size. 1174 An AP aggregates NAL units within one access unit. Each NAL unit to 1175 be carried in an AP is encapsulated in an aggregation unit. NAL 1176 units aggregated in one AP are in NAL unit decoding order. 1178 An AP consists of a payload header (denoted as PayloadHdr) followed 1179 by two or more aggregation units, as shown in Figure 4. 1181 0 1 2 3 1182 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 1183 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1184 | PayloadHdr (Type=48) | | 1185 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1186 | | 1187 | two or more aggregation units | 1188 | | 1189 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1190 | :...OPTIONAL RTP padding | 1191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1193 Figure 4 The structure of an aggregation packet 1195 The fields in the payload header are set as follows. The F bit MUST 1196 be equal to 0 if the F bit of each aggregated NAL unit is equal to 1197 zero; otherwise, it MUST be equal to 1. The Type field MUST be 1198 equal to 48. The value of LayerId MUST be equal to the lowest value 1199 of LayerId of all the aggregated NAL units. The value of TID MUST 1200 be the lowest value of TID of all the aggregated NAL units. 1202 Informative Note: All VCL NAL units in an AP have the same TID 1203 value since they belong to the same access unit. However, an AP 1204 may contain non-VCL NAL units for which the TID value in the NAL 1205 unit header may be different than the TID value of the VCL NAL 1206 units in the same AP. 1208 An AP MUST carry at least two aggregation units and can carry as 1209 many aggregation units as necessary; however, the total amount of 1210 data in an AP obviously MUST fit into an IP packet, and the size 1211 SHOULD be chosen so that the resulting IP packet is smaller than the 1212 MTU size so to avoid IP layer fragmentation. An AP MUST NOT contain 1213 Fragmentation Units (FUs) specified in section 4.8. APs MUST NOT be 1214 nested; i.e. an AP MUST NOT contain another AP. 1216 The first aggregation unit in an AP consists of a conditional 16-bit 1217 DONL field (in network byte order) followed by a 16-bit unsigned 1218 size information (in network byte order) that indicates the size of 1219 the NAL unit in bytes (excluding these two octets, but including the 1220 NAL unit header), followed by the NAL unit itself, including its NAL 1221 unit header, as shown in Figure 5. 1223 0 1 2 3 1224 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 1225 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1226 : DONL (conditional) | NALU size | 1227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1228 | NALU size | | 1229 +-+-+-+-+-+-+-+-+ NAL unit | 1230 | | 1231 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1232 | : 1233 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1235 Figure 5 The structure of the first aggregation unit in an AP 1237 The DONL field, when present, specifies the value of the 16 least 1238 significant bits of the decoding order number of the aggregated NAL 1239 unit. 1241 If tx-mode is equal to "MST" or sprop-max-don-diff is greater than 1242 0, the DONL field MUST be present in an aggregation unit that is the 1243 first aggregation unit in an AP, and the variable DON for the 1244 aggregated NAL unit is derived as equal to the value of the DONL 1245 field. Otherwise (tx-mode is equal to "SST" and sprop-max-don-diff 1246 is equal to 0), the DONL field MUST NOT be present in an aggregation 1247 unit that is the first aggregation unit in an AP. 1249 An aggregation unit that is not the first aggregation unit in an AP 1250 consists of a conditional 8-bit DOND field followed by a 16-bit 1251 unsigned size information (in network byte order) that indicates the 1252 size of the NAL unit in bytes (excluding these two octets, but 1253 including the NAL unit header), followed by the NAL unit itself, 1254 including its NAL unit header, as shown in Figure 6. 1256 0 1 2 3 1257 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 1258 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1259 : DOND (cond) | NALU size | 1260 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1261 | | 1262 | NAL unit | 1263 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1264 | : 1265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1267 Figure 6 The structure of an aggregation unit that is not the first 1268 aggregation unit in an AP 1270 When present, the DOND field plus 1 specifies the difference between 1271 the decoding order number values of the current aggregated NAL unit 1272 and the preceding aggregated NAL unit in the same AP. 1274 If tx-mode is equal to "MST" or sprop-max-don-diff is greater than 1275 0, the DOND field MUST be present in an aggregation unit that is not 1276 the first aggregation unit in an AP, and the variable DON for the 1277 aggregated NAL unit is derived as equal to the DON of the preceding 1278 aggregated NAL unit in the same AP plus the value of the DOND field 1279 plus 1 modulo 65536. Otherwise (tx-mode is equal to "SST" and 1280 sprop-max-don-diff is equal to 0), the DOND field MUST NOT be 1281 present in an aggregation unit that is not the first aggregation 1282 unit in an AP, and in this case the transmission order and decoding 1283 order of NAL units carried in the AP are the same as the order the 1284 NAL units appear in the AP. 1286 Figure 7 presents an example of an AP that contains two aggregation 1287 units, labeled as 1 and 2 in the figure, without the DONL and DOND 1288 fields being present. 1290 0 1 2 3 1291 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 1292 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1293 | RTP Header | 1294 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1295 | PayloadHdr (Type=48) | NALU 1 Size | 1296 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1297 | NALU 1 HDR | | 1298 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NALU 1 Data | 1299 | . . . | 1300 | | 1301 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1302 | . . . | NALU 2 Size | NALU 2 HDR | 1303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1304 | NALU 2 HDR | | 1305 +-+-+-+-+-+-+-+-+ NALU 2 Data | 1306 | . . . | 1307 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1308 | :...OPTIONAL RTP padding | 1309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1311 Figure 7 An example of an AP packet containing two aggregation units 1312 without the DONL and DOND fields 1314 Figure 8 presents an example of an AP that contains two aggregation 1315 units, labeled as 1 and 2 in the figure, with the DONL and DOND 1316 fields being present. 1318 0 1 2 3 1319 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 1320 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1321 | RTP Header | 1322 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1323 | PayloadHdr (Type=48) | NALU 1 DONL | 1324 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1325 | NALU 1 Size | NALU 1 HDR | 1326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1327 | | 1328 | NALU 1 Data . . . | 1329 | | 1330 + . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1331 | | NALU 2 DOND | NALU 2 Size | 1332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1333 | NALU 2 HDR | | 1334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NALU 2 Data | 1335 | | 1336 | . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1337 | :...OPTIONAL RTP padding | 1338 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1340 Figure 8 An example of an AP containing two aggregation units with 1341 the DONL and DOND fields 1343 4.8 Fragmentation Units (FUs) 1345 Fragmentation units (FUs) are introduced to enable fragmenting a 1346 single NAL unit into multiple RTP packets, possibly without 1347 cooperation or knowledge of the HEVC encoder. A fragment of a NAL 1348 unit consists of an integer number of consecutive octets of that NAL 1349 unit. Fragments of the same NAL unit MUST be sent in consecutive 1350 order with ascending RTP sequence numbers (with no other RTP packets 1351 within the same RTP stream being sent between the first and last 1352 fragment). 1354 When a NAL unit is fragmented and conveyed within FUs, it is 1355 referred to as a fragmented NAL unit. APs MUST NOT be fragmented. 1356 FUs MUST NOT be nested; i.e. an FU MUST NOT contain a subset of 1357 another FU. 1359 The RTP timestamp of an RTP packet carrying an FU is set to the 1360 NALU-time of the fragmented NAL unit. 1362 An FU consists of a payload header (denoted as PayloadHdr), an FU 1363 header of one octet, a conditional 16-bit DONL field (in network 1364 byte order), and an FU payload, as shown in Figure 9. 1366 0 1 2 3 1367 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 1368 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1369 | PayloadHdr (Type=49) | FU header | DONL (cond) | 1370 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 1371 | DONL (cond) | | 1372 |-+-+-+-+-+-+-+-+ | 1373 | FU payload | 1374 | | 1375 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1376 | :...OPTIONAL RTP padding | 1377 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1379 Figure 9 The structure of an FU 1381 The fields in the payload header are set as follows. The Type field 1382 MUST be equal to 49. The fields F, LayerId, and TID MUST be equal 1383 to the fields F, LayerId, and TID, respectively, of the fragmented 1384 NAL unit. 1386 The FU header consists of an S bit, an E bit, and a 6-bit FuType 1387 field, as shown in Figure 10. 1389 +---------------+ 1390 |0|1|2|3|4|5|6|7| 1391 +-+-+-+-+-+-+-+-+ 1392 |S|E| FuType | 1393 +---------------+ 1395 Figure 10 The structure of FU header 1397 The semantics of the FU header fields are as follows: 1398 S: 1 bit 1399 When set to one, the S bit indicates the start of a fragmented 1400 NAL unit i.e. the first byte of the FU payload is also the first 1401 byte of the payload of the fragmented NAL unit. When the FU 1402 payload is not the start of the fragmented NAL unit payload, the 1403 S bit MUST be set to zero. 1405 E: 1 bit 1406 When set to one, the E bit indicates the end of a fragmented NAL 1407 unit, i.e. the last byte of the payload is also the last byte of 1408 the fragmented NAL unit. When the FU payload is not the last 1409 fragment of a fragmented NAL unit, the E bit MUST be set to zero. 1411 FuType: 6 bits 1412 The field FuType MUST be equal to the field Type of the 1413 fragmented NAL unit. 1415 The DONL field, when present, specifies the value of the 16 least 1416 significant bits of the decoding order number of the fragmented NAL 1417 unit. 1419 If tx-mode is equal to "MST" or sprop-max-don-diff is greater than 1420 0, and the S bit is equal to 1, the DONL field MUST be present in 1421 the FU, and the variable DON for the fragmented NAL unit is derived 1422 as equal to the value of the DONL field. Otherwise (tx-mode is 1423 equal to "SST" and sprop-max-don-diff is equal to 0, or the S bit is 1424 equal to 0), the DONL field MUST NOT be present in the FU. 1426 A non-fragmented NAL unit MUST NOT be transmitted in one FU; i.e. 1427 the Start bit and End bit MUST NOT both be set to one in the same FU 1428 header. 1430 The FU payload consists of fragments of the payload of the 1431 fragmented NAL unit so that if the FU payloads of consecutive FUs, 1432 starting with an FU with the S bit equal to 1 and ending with an FU 1433 with the E bit equal to 1, are sequentially concatenated, the 1434 payload of the fragmented NAL unit can be reconstructed. The NAL 1435 unit header of the fragmented NAL unit is not included as such in 1436 the FU payload, but rather the information of the NAL unit header of 1437 the fragmented NAL unit is conveyed in F, LayerId, and TID fields of 1438 the FU payload headers of the FUs and the FuType field of the FU 1439 header of the FUs. An FU payload MUST not be empty. 1441 If an FU is lost, the receiver SHOULD discard all following 1442 fragmentation units in transmission order corresponding to the same 1443 fragmented NAL unit, unless the decoder in the receiver is known to 1444 be prepared to gracefully handle incomplete NAL units. 1446 A receiver in an endpoint or in a MANE MAY aggregate the first n-1 1447 fragments of a NAL unit to an (incomplete) NAL unit, even if 1448 fragment n of that NAL unit is not received. In this case, the 1449 forbidden_zero_bit of the NAL unit MUST be set to one to indicate a 1450 syntax violation. 1452 4.9 PACI packets 1454 This section specifies the PACI packet structure. The basic payload 1455 header specified in this memo is intentionally limited to the 16 1456 bits of the NAL unit header so to keep the packetization overhead to 1457 a minimum. However, cases have been identified where it is 1458 advisable to include control information in an easily accessible 1459 position in the packet header, despite the additional overhead. One 1460 such control information is the Temporal Scalability Control 1461 Information as specified in section 4.10 below. PACI packets carry 1462 this and future, similar structures. 1464 The PACI packet structure is based on a payload header extension 1465 mechanism that is generic and extensible to carry payload header 1466 extensions. In this section, the focus lies on the use within this 1467 specification. Section 4.9.2 below provides guidance for the 1468 specification designers in how to employ the extension mechanism in 1469 future specifications. 1471 A PACI packet consists of a payload header (denoted as PayloadHdr), 1472 for which the structure follows what is described in section 4.3 1473 above. The payload header is followed by the fields A, cType, 1474 PHSsize, F[0..2] and Y. 1476 Figure 11 shows a PACI packet in compliance with this memo; that is, 1477 without any extensions. 1479 0 1 2 3 1480 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 1481 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1482 | PayloadHdr (Type=50) |A| cType | PHSsize |F0..2|Y| 1483 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1484 | Payload Header Extension Structure (PHES) | 1485 |=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=| 1486 | | 1487 | PACI payload: NAL unit | 1488 | . . . | 1489 | | 1490 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1491 | :...OPTIONAL RTP padding | 1492 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1494 Figure 11 The structure of a PACI 1496 The fields in the payload header are set as follows. The F bit MUST 1497 be equal to 0. The Type field MUST be equal to 50. The value of 1498 LayerId MUST be a copy of the LayerId field of the PACI payload NAL 1499 unit or NAL-unit-like structure. The value of TID MUST be a copy of 1500 the TID field of the PACI payload NAL unit or NAL-unit-like 1501 structure. 1503 The semantics of other fields are as follows: 1505 A: 1 bit 1506 Copy of the F bit of the PACI payload NAL unit or NAL-unit-like 1507 structure. 1509 cType: 6 bits 1510 Copy of the Type field of the PACI payload NAL unit or NAL-unit- 1511 like structure. 1513 PHSsize: 5 bits 1514 Indicates the total length of the fields F[0..2], Y, and PHES. 1515 The value is limited to be less than or equal to 32 octets, to 1516 simplify encoder design for MTU size matching. 1518 F0 1519 This field equal to 1 specifies the presence of a temporal 1520 scalability support extension in the PHES. 1522 F1, F2 1523 MUST be 0, available for future extensions, see section 4.9.2. 1525 Y: 1 bit 1526 MUST be 0, available for future extensions, see section 4.9.2. 1528 PHES: variable number of octets 1529 A variable number of octets as indicated by the value of PHSsize. 1531 PACI Payload 1532 The NAL unit or NAL-unit-like structure (such as: FU or AP) to be 1533 carried, not including the first two octets. 1535 Informative note: The first two octets of the NAL unit or NAL- 1536 unit-like structure carried in the PACI payload are not 1537 included in the PACI payload. Rather, the respective values 1538 are copied in locations of the PayloadHdr of the RTP packet. 1539 This design offers two advantages: first, the overall 1540 structure of the payload header is preserved, i.e. there is no 1541 special case of payload header structure that needs to be 1542 implemented for PACI. Second, no additional overhead is 1543 introduced. 1545 A PACI payload MAY be a single NAL unit, an FU, or an AP. PACIs 1546 MUST NOT be fragmented or aggregated. The following subsection 1547 documents the reasons for these design choices. 1549 4.9.1 Reasons for the PACI rules (informative) 1551 A PACI cannot be fragmented. If a PACI could be fragmented, and a 1552 fragment other than the first fragment would get lost, access to the 1553 information in the PACI would not be possible. Therefore, a PACI 1554 must not be fragmented. In other words, an FU must not carry 1555 (fragments of) a PACI. 1557 A PACI cannot be aggregated. Aggregation of PACIs is inadvisable 1558 from a compression viewpoint, as, in many cases, several to be 1559 aggregated NAL units would share identical PACI fields and values 1560 which would be carried redundantly for no reason. Most, if not all 1561 the practical effects of PACI aggregation can be achieved by 1562 aggregating NAL units and bundling them with a PACI (see below). 1563 Therefore, a PACI must not be aggregated. In other words, an AP 1564 must not contain a PACI. 1566 The payload of a PACI can be a fragment. Both middleboxes and 1567 sending systems with inflexible (often hardware-based) encoders 1568 occasionally find themselves in situations where a PACI and its 1569 headers, combined, are larger than the MTU size. In such a 1570 scenario, the middlebox or sender can fragment the NAL unit and 1571 encapsulate the fragment in a PACI. Doing so preserves the payload 1572 header extension information for all fragments, allowing downstream 1573 middleboxes and the receiver to take advantage of that information. 1574 Therefore, a sender may place a fragment into a PACI, and a receiver 1575 must be able to handle such a PACI. 1577 The payload of a PACI can be an aggregation NAL unit. HEVC 1578 bitstreams can contain unevenly sized and/or small (when compared to 1579 the MTU size) NAL units. In order to efficiently packetize such 1580 small NAL units, AP were introduced. The benefits of APs are 1581 independent from the need for a payload header extension. 1582 Therefore, a sender may place an AP into a PACI, and a receiver must 1583 be able to handle such a PACI. 1585 4.9.2 PACI extensions (Informative) 1587 This subsection includes recommendations for future specification 1588 designers on how to extent the PACI syntax to accommodate future 1589 extensions. Obviously, designers are free to specify whatever 1590 appears to be appropriate to them at the time of their design. 1591 However, a lot of thought has been invested into the extension 1592 mechanism described below, and we suggest that deviations from it 1593 warrant a good explanation. 1595 This memo defines only a single payload header extension (Temporal 1596 Scalability Control Information, described below in section 4.10), 1597 and, therefore, only the F0 bit carries semantics. F1 and F2 are 1598 already named (and not just marked as reserved, as a typical video 1599 spec designer would do). They are intended to signal two additional 1600 extensions. The Y bit allows to, recursively, add further F and Y 1601 bits to extend the mechanism beyond 3 possible payload header 1602 extensions. It is suggested to define a new packet type (using a 1603 different value for Type) when assigning the F1, F2, or Y bits 1604 different semantics than what is suggested below. 1606 When a Y bit is set, an 8 bit flag-extension is inserted after the Y 1607 bit. A flag-extension consists of 7 flags F[n..n+6], and another Y 1608 bit. 1610 The basic PACI header already includes F0, F1, and F2. Therefore, 1611 the Fx bits in the first flag-extensions are numbered F3, F4, ..., 1612 F9, the F bits in the second flag-extension are numbered F10, F11, 1613 ..., F16, and so forth. As a result, at least 3 Fx bits are always 1614 in the PACI, but the number of Fx bits (and associated types of 1615 extensions), can be increased by setting the next Y bit and adding 1616 an octet of flag-extensions, carrying 7 flags and another Y bit. 1617 The size of this list of flags is subject to the limits specified in 1618 section 4.9 (32 octets for all flag-extensions and the PHES 1619 information combined). 1621 Each of the F bits can indicate either the presence of information 1622 in the Payload Header Extension Structure (PHES), described below, 1623 or a given F bit can indicate a certain condition, without including 1624 additional information in the PHES. 1626 When a spec developer devises a new syntax that takes advantage of 1627 the PACI extension mechanism, he/she must follow the constraints 1628 listed below; otherwise the extension mechanism may break. 1630 1) The fields added for a particular Fx bit MUST be fixed in 1631 length and not depend on what other Fx bits are set (no parsing 1632 dependency). 1633 2) The Fx bits must be assigned in order. 1634 3) An implementation that supports the n-th Fn bit for any value 1635 of n must understand the syntax (though not necessarily the 1636 semantics) of the fields Fk (with k < n), so to be able to 1637 either use those bits when present, or at least be able to skip 1638 over them. 1640 4.10 Temporal Scalability Control Information 1642 This section describes the single payload header extension defined 1643 in this specification, known as Temporal Scalability Control 1644 Information (TSCI). If, in the future, additional payload header 1645 extensions become necessary, they could be specified in this section 1646 of an updated version of this document, or in their own documents. 1648 When F0 is set to 1 in a PACI, this specifies that the PHES field 1649 includes the TSCI fields TL0REFIDX, IrapPicID, S, and E as follows: 1651 0 1 2 3 1652 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 1653 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1654 | PayloadHdr (Type=50) |A| cType | PHSsize |F0..2|Y| 1655 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1656 | TL0REFIDX | IrapPicID |S|E|RES| | 1657 |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1658 | .... | 1659 | PACI payload: NAL unit | 1660 | | 1661 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1662 | :...OPTIONAL RTP padding | 1663 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1665 Figure 12 The structure of a PACI with a PHES containing a TSCI 1667 TL0PICIDX (8 bits) 1668 When present, the TL0PICIDX field MUST be set to equal to 1669 temporal_sub_layer_zero_idx as specified in Section D.3.32 of 1670 [H.265] for the access unit containing the NAL unit in the PACI. 1672 IrapPicID (8 bits) 1673 When present, the IrapPicID field MUST be set to equal to 1674 irap_pic_id as specified in Section D.3.22 of [H.265] for the 1675 access unit containing the NAL unit in the PACI. 1677 S (1 bit) 1678 The S bit MUST be set to 1 if any of the following conditions is 1679 true and MUST be set to 0 otherwise: 1681 . The NAL unit in the payload of the PACI is the first VCL NAL 1682 unit, in decoding order, of a picture. 1683 . The NAL unit in the payload of the PACI is an AP and the NAL 1684 unit in the first contained aggregation unit is the first VCL 1685 NAL unit, in decoding order, of a picture. 1686 . The NAL unit in the payload of the PACI is an FU with its S bit 1687 equal to 1 and the FU payload containing a fragment of the 1688 first VCL NAL unit, in decoding order of a picture. 1690 E (1 bit) 1691 The E bit MUST be set to 1 if any of the following conditions is 1692 true and MUST be set to 0 otherwise: 1694 . The NAL unit in the payload of the PACI is the last VCL NAL 1695 unit, in decoding order, of a picture. 1696 . The NAL unit in the payload of the PACI is an AP and the NAL 1697 unit in the last contained aggregation unit is the last VCL NAL 1698 unit, in decoding order, of a picture. 1699 . The NAL unit in the payload of the PACI is an FU with its E bit 1700 equal to 1 and the FU payload containing a fragment of the last 1701 VCL NAL unit, in decoding order of a picture. 1703 RES (2 bits) 1704 MUST be equal to 0. Reserved for future extensions. 1706 The value of PHSsize MUST be set to 3. Receivers MUST allow other 1707 values of the fields F0, F1, F2, Y, and PHSsize, and MUST ignore any 1708 additional fields, when present, than specified above in the PHES. 1710 5. Packetization Rules 1712 The following packetization rules apply: 1714 o If tx-mode is equal to "MST" or sprop-max-don-diff is greater 1715 than 0 for an RTP stream, the transmission order of NAL units 1716 carried in the RTP stream MAY be different than the NAL unit 1717 decoding order. Otherwise (tx-mode is equal to "SST" and sprop- 1718 max-don-diff is equal to 0 for an RTP stream), the transmission 1719 order of NAL units carried in the RTP stream MUST be the same as 1720 the NAL unit decoding order. 1722 o A NAL unit of a small size SHOULD be encapsulated in an 1723 aggregation packet together with one or more other NAL units in 1724 order to avoid the unnecessary packetization overhead for small 1725 NAL units. For example, non-VCL NAL units such as access unit 1726 delimiters, parameter sets, or SEI NAL units are typically small 1727 and can often be aggregated with VCL NAL units without violating 1728 MTU size constraints. 1730 o Each non-VCL NAL unit SHOULD, when possible from an MTU size 1731 match viewpoint, be encapsulated in an aggregation packet 1732 together with its associated VCL NAL unit, as typically a non-VCL 1733 NAL unit would be meaningless without the associated VCL NAL unit 1734 being available. 1736 o For carrying exactly one NAL unit in an RTP packet, a single NAL 1737 unit packet MUST be used. 1739 6. De-packetization Process 1741 The general concept behind de-packetization is to get the NAL units 1742 out of the RTP packets in an RTP stream and all the dependent RTP 1743 streams, if any, and pass them to the decoder in the NAL unit 1744 decoding order. 1746 The de-packetization process is implementation dependent. 1747 Therefore, the following description should be seen as an example of 1748 a suitable implementation. Other schemes may be used as well as 1749 long as the output for the same input is the same as the process 1750 described below. The output is the same when the set of output NAL 1751 units and their order are both identical. Optimizations relative to 1752 the described algorithms are possible. 1754 All normal RTP mechanisms related to buffer management apply. In 1755 particular, duplicated or outdated RTP packets (as indicated by the 1756 RTP sequences number and the RTP timestamp) are removed. To 1757 determine the exact time for decoding, factors such as a possible 1758 intentional delay to allow for proper inter-stream synchronization 1759 must be factored in. 1761 NAL units with NAL unit type values in the range of 0 to 47, 1762 inclusive may be passed to the decoder. NAL-unit-like structures 1763 with NAL unit type values in the range of 48 to 63, inclusive, MUST 1764 NOT be passed to the decoder. 1766 The receiver includes a receiver buffer, which is used to compensate 1767 for transmission delay jitter within individual RTP streams and 1768 across RTP streams, to reorder NAL units from transmission order to 1769 the NAL unit decoding order, and to recover the NAL unit decoding 1770 order in MST, when applicable. In this section, the receiver 1771 operation is described under the assumption that there is no 1772 transmission delay jitter within a packet stream and across RTP 1773 streams. To make a difference from a practical receiver buffer that 1774 is also used for compensation of transmission delay jitter, the 1775 receiver buffer is here after called the de-packetization buffer in 1776 this section. Receivers should also prepare for transmission delay 1777 jitter; i.e. either reserve separate buffers for transmission delay 1778 jitter buffering and de-packetization buffering or use a receiver 1779 buffer for both transmission delay jitter and de-packetization. 1780 Moreover, receivers should take transmission delay jitter into 1781 account in the buffering operation; e.g. by additional initial 1782 buffering before starting of decoding and playback. 1784 If only one RTP stream is being received and sprop-max-don-diff of 1785 the only RTP stream being received is equal to 0, the de- 1786 packetization buffer size is zero bytes, i.e. the NAL units carried 1787 in the RTP stream are directly passed to the decoder in their 1788 transmission order, which is identical to the decoding order of the 1789 NAL units. Otherwise, the process described in the remainder of this 1790 section applies. 1792 There are two buffering states in the receiver: initial buffering 1793 and buffering while playing. Initial buffering starts when the 1794 reception is initialized. After initial buffering, decoding and 1795 playback are started, and the buffering-while-playing mode is used. 1797 Regardless of the buffering state, the receiver stores incoming NAL 1798 units, in reception order, into the de-packetization buffer. NAL 1799 units carried in RTP packets are stored in the de-packetization 1800 buffer individually, and the value of AbsDon is calculated and 1801 stored for each NAL unit. When MST is in use, NAL units of all RTP 1802 streams of a bitstream are stored in the same de-packetization 1803 buffer. When NAL units carried in any two RTP streams are available 1804 to be placed into the de-packetization buffer, those NAL units 1805 carried in the RTP stream that is lower in the dependency tree are 1806 placed into the buffer first. For example, if RTP stream A depends 1807 on RTP stream B, then NAL units carried in RTP stream B are placed 1808 into the buffer first. 1810 Initial buffering lasts until condition A (the difference between 1811 the greatest and smallest AbsDon values of the NAL units in the de- 1812 packetization buffer is greater than or equal to the value of sprop- 1813 max-don-diff of the highest RTP stream) or condition B (the number 1814 of NAL units in the de-packetization buffer is greater than the 1815 value of sprop-depack-buf-nalus) is true. 1817 After initial buffering, whenever condition A or condition B is 1818 true, the following operation is repeatedly applied until both 1819 condition A and condition A become false: 1821 o The NAL unit in the de-packetization buffer with the smallest 1822 value of AbsDon is removed from the de-packetization buffer and 1823 passed to the decoder. 1825 When no more NAL units are flowing into the de-packetization buffer, 1826 all NAL units remaining in the de-packetization buffer are removed 1827 from the buffer and passed to the decoder in the order of increasing 1828 AbsDon values. 1830 7. Payload Format Parameters 1832 This section specifies the parameters that MAY be used to select 1833 optional features of the payload format and certain features or 1834 properties of the bitstream or the RTP stream. The parameters are 1835 specified here as part of the media type registration for the HEVC 1836 codec. A mapping of the parameters into the Session Description 1837 Protocol (SDP) [RFC4566] is also provided for applications that use 1838 SDP. Equivalent parameters could be defined elsewhere for use with 1839 control protocols that do not use SDP. 1841 7.1 Media Type Registration 1843 The media subtype for the HEVC codec is allocated from the IETF 1844 tree. 1846 The receiver MUST ignore any unrecognized parameter. 1848 Media Type name: video 1850 Media subtype name: H265 1852 Required parameters: none 1854 OPTIONAL parameters: 1856 profile-space, profile-id: 1858 The profile-space parameter indicates the context for 1859 interpretation of the profile-id parameter value. The 1860 profile, which specifies the subset of coding tools that may 1861 have been used to generate the bitstream or that the receiver 1862 supports, as specified in [HEVC], is defined by the 1863 combination of profile-space and profile-id. 1865 The value of profile-space MUST be in the range of 0 to 3, 1866 inclusive. The value of profile-id MUST be in the range of 0 1867 to 31, inclusive. 1869 If the profile-space and profile-id parameters are used to 1870 indicate properties of a bitstream, it indicates that, to 1871 decode the bitstream, the minimum subset of coding tools a 1872 decoder has to support is the profile specified by both 1873 parameters. 1875 If the profile-space and profile-id parameters are used for 1876 capability exchange or session setup, it indicates the subset 1877 of coding tools, which is equal to the profile, that the codec 1878 supports for both receiving and sending. 1880 If no profile-space is present, a value of 0 MUST be inferred 1881 and if no profile-id is present the Main profile (i.e. a value 1882 of 1) MUST be inferred. 1884 When used to indicate properties of a bitstream, the profile- 1885 space and profile-id parameters are derived from the SPS or 1886 VPS NAL units as follows, where general_profile_space, 1887 general_profile_idc, sub_layer_profile_space[j], and 1888 sub_layer_profile_idc[j] are specified in [HEVC]. 1890 If the RTP stream is the highest RTP stream, the following 1891 applies: 1893 o profile_space = general_profile_space 1894 o profile_id = general_profile_idc 1896 Otherwise (the RTP stream is a dependent RTP stream), the 1897 following applies, with j being the value of the sprop-sub- 1898 layer-id parameter: 1900 o profile_space = sub_layer_profile_space[j] 1901 o profile_id = sub_layer_profile_idc[j] 1903 tier-flag, level-id: 1905 The tier-flag parameter indicates the context for 1906 interpretation of the level-id value. The default level, 1907 which limits values of syntax elements or on arithmetic 1908 combinations of values of syntax elements, as specified in 1910 [HEVC], is defined by the combination of tier-flag and level- 1911 id. 1913 The value of tier-flag MUST be in the range of 0 to 1, 1914 inclusive. The value of level-id MUST be in the range of 0 1915 to 255, inclusive. 1917 If the tier-flag and level-id parameters are used to indicate 1918 properties of a bitstream, it indicates that, to decode the 1919 bitstream the lowest level the decoder has to support is the 1920 default level. 1922 If the tier-flag and level-id parameters are used for 1923 capability exchange or session setup, the following applies. 1924 If max-recv-level-id is not present, the default level defined 1925 by tier-flag and level-id indicates the highest level the 1926 codec wishes to support. Otherwise, tier-flag and max-recv- 1927 level-id indicate the highest level the codec supports for 1928 receiving. For either receiving or sending, all levels that 1929 are lower than the highest level supported MUST also be 1930 supported. 1932 If no tier-flag is present, a value of 0 MUST be inferred and 1933 if no level-id is present, a value of 93 (i.e. level 3.1) MUST 1934 be inferred. 1936 When used to indicate properties of a bitstream, the tier-flag 1937 and level-id parameters are derived from the SPS or VPS NAL 1938 units as follows, where general_tier_flag, general_level_idc, 1939 sub_layer_tier_flag[j], and sub_layer_level_idc[j] are 1940 specified in [HEVC]. 1942 If the RTP stream is the highest RTP stream, the following 1943 applies: 1945 o tier-flag = general_tier_flag 1946 o level-id = general_level_idc 1948 Otherwise (the RTP stream is a dependent RTP stream), the 1949 following applies, with j being the value of the sprop-sub- 1950 layer-id parameter: 1952 o tier-flag = sub_layer_tier_flag[j] 1953 o level-id = sub_layer_level_idc[j] 1955 interop-constraints: 1957 A base16 [RFC4648] (hexadecimal) representation of six bytes 1958 of data, consisting of progressive_source_flag, 1959 interlaced_source_flag, non_packed_constraint_flag, 1960 frame_only_constraint_flag, and reserved_zero_44bits. 1962 If the interop-constraints parameter is not present, the 1963 following MUST be inferred: 1965 o progressive_source_flag = 1 1966 o interlaced_source_flag = 0 1967 o non_packed_constraint_flag = 1 1968 o frame_only_constraint_flag = 1 1969 o reserved_zero_44bits = 0 1971 When the interop-constraints parameter is used to indicate 1972 properties of a bitstream, the following applies, where 1973 general_progressive_source_flag, 1974 general_interlaced_source_flag, 1975 general_non_packed_constraint_flag, 1976 general_non_packed_constraint_flag, 1977 general_frame_only_constraint_flag, 1978 general_reserved_zero_44bits, 1979 sub_layer_progressive_source_flag[j], 1980 sub_layer_interlaced_source_flag[j], 1981 sub_layer_non_packed_constraint_flag[j], 1982 sub_layer_frame_only_constraint_flag[j], and 1983 sub_layer_reserved_zero_44bits[j] are specified in [HEVC]. 1985 If the RTP stream is the highest RTP stream, the following 1986 applies: 1988 o progressive_source_flag = general_progressive_source_flag 1989 o interlaced_source_flag = general_interlaced_source_flag 1990 o non_packed_constraint_flag = 1991 general_non_packed_constraint_flag 1992 o frame_only_constraint_flag = 1993 general_frame_only_constraint_flag 1994 o reserved_zero_44bits = general_reserved_zero_44bits 1996 Otherwise (the RTP stream is a dependent RTP stream), the 1997 following applies, with j being the value of the sprop-sub- 1998 layer-id parameter: 2000 o progressive_source_flag = 2001 sub_layer_progressive_source_flag[j] 2002 o interlaced_source_flag = 2003 sub_layer_interlaced_source_flag[j] 2004 o non_packed_constraint_flag = 2005 sub_layer_non_packed_constraint_flag[j] 2006 o frame_only_constraint_flag = 2007 sub_layer_frame_only_constraint_flag[j] 2008 o reserved_zero_44bits = sub_layer_reserved_zero_44bits[j] 2010 When the interop-constraints parameter is used for capability 2011 exchange or session setup, for both the sent bitstream, when 2012 present, and the received bitstream, when present, the values 2013 of general_progressive_source_flag, 2014 general_interlaced_source_flag, 2015 general_non_packed_constraint_flag, 2016 general_frame_only_constraint_flag, and 2017 general_reserved_zero_44bits in the SPS or VPS NAL units MUST 2018 be equal to progressive_source_flag, interlaced_source_flag, 2019 non_packed_constraint_flag, frame_only_constraint_flag, and 2020 reserved_zero_44bits, respectively, and for any value of j, 2021 the values of sub_layer_progressive_source_flag[j], 2022 sub_layer_interlaced_source_flag[j], 2023 sub_layer_non_packed_constraint_flag[j], 2024 sub_layer_frame_only_constraint_flag[j], and 2025 sub_layer_reserved_zero_44bits[j] in the SPS or VPS NAL units 2026 MUST be equal to progressive_source_flag, 2027 interlaced_source_flag, non_packed_constraint_flag, 2028 frame_only_constraint_flag, and reserved_zero_44bits, 2029 respectively. 2031 profile-compatibility-indicator: 2033 A base16 [RFC4648] representation of the four bytes 2034 representing the 32 profile compatibility flags in the SPS or 2035 VPS NAL units. A decoder conforming to a certain profile may 2036 be able to decode bitstreams conforming to other profiles. 2037 The profile-compatibility-indicator provides exact information 2038 of the ability of a decoder conforming to a certain profile to 2039 decode bitstreams conforming to another profile. More 2040 concretely, if the profile compatibility flag corresponding to 2041 the profile a decoder conforms to is set, then the decoder is 2042 able to decode any bitstream with the flag set, irrespective 2043 of the profile the bitstream conforms to (provided that the 2044 decoder supports the highest level of the bitstream). 2046 When profile-compatibility-indicator is used to indicate 2047 properties of a bitstream, the following applies, where 2048 general_profile_compatibility_flag[j] and 2049 sub_layer_profile_compatibility_flag[i][j] are specified in 2050 [HEVC]. 2052 If the RTP stream is the highest RTP stream, the following 2053 applies with j = 0..31: 2055 o The 32 flags = general_profile_compatibility_flag[j] 2057 Otherwise (the RTP stream is a dependent RTP stream), the 2058 following applies with i being the value of the sprop-sub- 2059 layer-id parameter and j = 0..31: 2061 o The 32 flags = sub_layer_profile_compatibility_flag[i][j] 2063 When profile-compatibility-indicator is used for capability 2064 exchange or session setup, the values of 2065 general_profile_compatibility_flag[j] with j = 0..31 MUST be 2066 equal to bits 0 to 31, inclusive, of profile-compatibility- 2067 indicator, respectively, and for any value of i, the values of 2068 sub_layer_profile_compatibility_flag[i][j] with j = 0..31 MUST 2069 be equal to bits 0 to 31, inclusive, of profile-compatibility- 2070 indicator, respectively. 2072 sprop-sub-layer-id: 2074 This parameter MAY be used to indicate the highest allowed 2075 value of TID in the bitstream. When not present, the value of 2076 sprop-sub-layer-id is inferred to be equal to 6. 2078 The value of sprop-sub-layer-id MUST be in the range of 0 2079 to 6, inclusive. 2081 recv-sub-layer-id: 2083 This parameter MAY be used to signal a receiver's choice of 2084 the offered or declared sub-layers in the sprop-vps. The 2085 value of recv-sub-layer-id indicates the TID of the highest 2086 sub-layer of the bitstream that a receiver supports. When not 2087 present, the value of recv-sub-layer-id is inferred to be 2088 equal to sprop-sub-layer-id. 2090 The value of recv-sub-layer-id MUST be in the range of 0 to 6, 2091 inclusive. 2093 max-recv-level-id: 2095 This parameter MAY be used, together with tier-flag, to 2096 indicate the highest level a receiver supports. The highest 2097 level the receiver supports is equal to the value of max-recv- 2098 level-id divided by 30 for the Main or High tier (as 2099 determined by tier-flag equal to 0 or 1, respectively). 2101 The value of max-recv-level-id MUST be in the range of 0 2102 to 255, inclusive. 2104 When max-recv-level-id is not present, the value is inferred 2105 to be equal to level-id. 2107 max-recv-level-id MUST NOT be present when the highest level 2108 the receiver supports is not higher than the default level. 2110 tx-mode: 2112 This parameter indicates whether the transmission mode is SST 2113 or MST. 2115 The value of tx-mode MUST be equal to either "MST" or "SST". 2116 When not present, the value of tx-mode is inferred to be equal 2117 to "SST". 2119 If the value is equal to "MST", MST MUST be in use. Otherwise 2120 (the value is equal to "SST"), SST MUST be in use. 2122 The value of tx-mode MUST be equal to "MST" for all RTP 2123 sessions in an MST. 2125 sprop-vps: 2127 This parameter MAY be used to convey any video parameter set 2128 NAL unit of the bitstream. When present, the parameter MAY be 2129 used to indicate codec capability and sub-stream 2130 characteristics (i.e. properties of sub-layer representations 2131 as defined in [HEVC]) as well as for out-of-band transmission 2132 of video parameter sets. The value of the parameter is a 2133 comma-separated (',') list of base64 [RFC4648] representations 2134 of the video parameter set NAL units as specified in Section 2135 7.3.2.1 of [HEVC]. 2137 sprop-sps: 2139 This parameter MAY be used to convey sequence parameter set 2140 NAL units of the bitstream for out-of-band transmission of 2141 sequence parameter sets. The value of the parameter is a 2142 comma-separated (',') list of base64 [RFC4648] representations 2143 of the sequence parameter set NAL units as specified in 2144 Section 7.3.2.2 of [HEVC]. 2146 sprop-pps: 2148 This parameter MAY be used to convey picture parameter set NAL 2149 units of the bitstream for out-of-band transmission of picture 2150 parameter sets. The value of the parameter is a comma- 2151 separated (',') list of base64 [RFC4648] representations of 2152 the picture parameter set NAL units as specified in Section 2153 7.3.2.3 of [HEVC]. 2155 sprop-sei: 2157 This parameter MAY be used to convey one or more SEI messages 2158 that describe bitstream characteristics. When present, a 2159 decoder can rely on the bitstream characteristics that are 2160 described in the SEI messages for the entire duration of the 2161 session, independently from the persistence scopes of the SEI 2162 messages as specified in [HEVC]. 2164 The value of the parameter is a comma-separated (',') list of 2165 base64 [RFC4648] representations of SEI NAL units as specified 2166 in Section 7.3.2.4 of [HEVC]. 2168 Informative note: Intentionally, no list of applicable or 2169 inapplicable SEI messages is specified here. Conveying 2170 certain SEI messages in sprop-sei may be sensible in some 2171 application scenarios and meaningless in others. However, 2172 a few examples are described below: 2174 1) In an environment where the encoded bitstream was 2175 created from film-based source material, and no splicing 2176 is going to occur during the lifetime of the session, 2177 the film grain characteristics SEI message or the tone 2178 mapping information SEI message are likely meaningful, 2179 and sending them in sprop-sei rather than in the 2180 bitstream at each entry point may help saving bits and 2181 allows to configure the renderer only once, avoiding 2182 unwanted artifacts. 2183 2) The structure of pictures information SEI message in 2184 sprop-sei can be used to inform a decoder of information 2185 on the NAL unit types, picture order count values, and 2186 prediction dependencies of a sequence of pictures. 2187 Having such knowledge can be helpful for error recovery. 2188 3) Examples for SEI messages that would be meaningless to 2189 be conveyed in sprop-sei include the decoded picture 2190 hash SEI message (it is close to impossible that all 2191 decoded pictures have the same hash-tag), the display 2192 orientation SEI message when the device is a handheld 2193 device (as the display orientation may change when the 2194 handheld device is turned around), or the filler payload 2195 SEI message (as there is no point in just having more 2196 bits in SDP). 2198 max-lsr, max-lps, max-cpb, max-dpb, max-br, max-tr, max-tc: 2200 These parameters MAY be used to signal the capabilities of a 2201 receiver implementation. These parameters MUST NOT be used 2202 for any other purpose. The highest level (specified by tier- 2203 flag and max-recv-level-id) MUST be such that the receiver is 2204 fully capable of supporting. max-lsr, max-lps, max-cpb, max- 2205 dpb, max-br, max-tr, and max-tc MAY be used to indicate 2206 capabilities of the receiver that extend the required 2207 capabilities of the highest level, as specified below. 2209 When more than one parameter from the set (max-lsr, max-lps, 2210 max-cpb, max-dpb, max-br, max-tr, max-tc) is present, the 2211 receiver MUST support all signaled capabilities 2212 simultaneously. For example, if both max-lsr and max-br are 2213 present, the highest level with the extension of both the 2214 picture rate and bitrate is supported. That is, the receiver 2215 is able to decode bitstreams in which the luma sample rate is 2216 up to max-lsr (inclusive), the bitrate is up to max-br 2217 (inclusive), the coded picture buffer size is derived as 2218 specified in the semantics of the max-br parameter below, and 2219 the other properties comply with the highest level specified 2220 by tier-flag and max-recv-level-id. 2222 Informative note: When the OPTIONAL media type parameters 2223 are used to signal the properties of a bitstream, and max- 2224 lsr, max-lps, max-cpb, max-dpb, max-br, max-tr, and max-tc 2225 are not present, the values of profile-space, profile-id, 2226 tier-flag, and level-id must always be such that the 2227 bitstream complies fully with the specified profile and 2228 level. 2230 max-lsr: 2231 The value of max-lsr is an integer indicating the maximum 2232 processing rate in units of luma samples per second. The max- 2233 lsr parameter signals that the receiver is capable of decoding 2234 video at a higher rate than is required by the highest level. 2236 When max-lsr is signaled, the receiver MUST be able to decode 2237 bitstreams that conform to the highest level, with the 2238 exception that the MaxLumaSR value in Table A-2 of [HEVC] for 2239 the highest level is replaced with the value of max-lsr. 2240 Senders MAY use this knowledge to send pictures of a given 2241 size at a higher picture rate than is indicated in the highest 2242 level. 2244 When not present, the value of max-lsr is inferred to be equal 2245 to the value of MaxLumaSR given in Table A-2 of [HEVC] for the 2246 highest level. 2248 The value of max-lsr MUST be in the range of MaxLumaSR to 2249 16 * MaxLumaSR, inclusive, where MaxLumaSR is given in Table 2250 A-2 of [HEVC] for the highest level. 2252 max-lps: 2253 The value of max-lps is an integer indicating the maximum 2254 picture size in units of luma samples. The max-lps parameter 2255 signals that the receiver is capable of decoding larger 2256 picture sizes than are required by the highest level. When 2257 max-lps is signaled, the receiver MUST be able to decode 2258 bitstreams that conform to the highest level, with the 2259 exception that the MaxLumaPS value in Table A-1 of [HEVC] for 2260 the highest level is replaced with the value of max-lps. 2261 Senders MAY use this knowledge to send larger pictures at a 2262 proportionally lower picture rate than is indicated in the 2263 highest level. 2265 When not present, the value of max-lps is inferred to be equal 2266 to the value of MaxLumaPS given in Table A-1 of [HEVC] for the 2267 highest level. 2269 The value of max-lps MUST be in the range of MaxLumaPS to 2270 16 * MaxLumaPS, inclusive, where MaxLumaPS is given in Table 2271 A-1 of [HEVC] for the highest level. 2273 max-cpb: 2274 The value of max-cpb is an integer indicating the maximum 2275 coded picture buffer size in units of CpbBrVclFactor bits for 2276 the VCL HRD parameters and in units of CpbBrNalFactor bits for 2277 the NAL HRD parameters, where CpbBrVclFactor and 2278 CpbBrNalFactor are defined in Section A.4 of [HEVC]. The max- 2279 cpb parameter signals that the receiver has more memory than 2280 the minimum amount of coded picture buffer memory required by 2281 the highest level. When max-cpb is signaled, the receiver 2282 MUST be able to decode bitstreams that conform to the highest 2283 level, with the exception that the MaxCPB value in Table A-1 2284 of [HEVC] for the highest level is replaced with the value of 2285 max-cpb. Senders MAY use this knowledge to construct coded 2286 bitstreams with greater variation of bitrate than can be 2287 achieved with the MaxCPB value in Table A-1 of [HEVC]. 2289 When not present, the value of max-cpb is inferred to be equal 2290 to the value of MaxCPB given in Table A-1 of [HEVC] for the 2291 highest level. 2293 The value of max-cpb MUST be in the range of MaxCPB to 2294 16 * MaxCPB, inclusive, where MaxLumaCPB is given in Table A-1 2295 of [HEVC] for the highest level. 2297 Informative note: The coded picture buffer is used in the 2298 hypothetical reference decoder (Annex C of HEVC). The use 2299 of the hypothetical reference decoder is recommended in 2300 HEVC encoders to verify that the produced bitstream 2301 conforms to the standard and to control the output bitrate. 2302 Thus, the coded picture buffer is conceptually independent 2303 of any other potential buffers in the receiver, including 2304 de-packetization and de-jitter buffers. The coded picture 2305 buffer need not be implemented in decoders as specified in 2306 Annex C of HEVC, but rather standard-compliant decoders can 2307 have any buffering arrangements provided that they can 2308 decode standard-compliant bitstreams. Thus, in practice, 2309 the input buffer for a video decoder can be integrated with 2310 de-packetization and de-jitter buffers of the receiver. 2312 max-dpb: 2313 The value of max-dpb is an integer indicating the maximum 2314 decoded picture buffer size in units decoded pictures at the 2315 MaxLumaPS for the highest level, i.e. the number of decoded 2316 pictures at the maximum picture size defined by the highest 2317 level. The value of max-dpb MUST be in the range of 1 to 16, 2318 respectively. The max-dpb parameter signals that the receiver 2319 has more memory than the minimum amount of decoded picture 2320 buffer memory required by default, which is MaxDpbPicBuf as 2321 defined in [HEVC] (equal to 6). When max-dpb is signaled, the 2322 receiver MUST be able to decode bitstreams that conform to the 2323 highest level, with the exception that the MaxDpbPicBuff value 2324 defined in [HEVC] as 6 is replaced with the value of max-dpb. 2325 Consequently, a receiver that signals max-dpb MUST be capable 2326 of storing the following number of decoded pictures 2327 (MaxDpbSize) in its decoded picture buffer: 2329 if( PicSizeInSamplesY <= ( MaxLumaPS >> 2 ) ) 2330 MaxDpbSize = Min( 4 * max-dpb, 16 ) 2331 else if ( PicSizeInSamplesY <= ( MaxLumaPS >> 1 ) ) 2332 MaxDpbSize = Min( 2 * max-dpb, 16 ) 2333 else if ( PicSizeInSamplesY <= ( ( 3 * MaxLumaPS ) >> 2 ) ) 2334 MaxDpbSize = Min( (4 * max-dpb) / 3, 16 ) 2335 else 2336 MaxDpbSize = max-dpb 2338 Wherein MaxLumaPS given in Table A-1 of [HEVC] for the highest 2339 level and PicSizeInSamplesY is the current size of each 2340 decoded picture in units of luma samples as defined in [HEVC]. 2342 The value of max-dpb MUST be greater than or equal to the 2343 value of MaxDpbPicBuf (i.e. 6) as defined in [HEVC]. Senders 2344 MAY use this knowledge to construct coded bitstreams with 2345 improved compression. 2347 When not present, the value of max-dpb is inferred to be equal 2348 to the value of MaxDpbPicBuf (i.e. 6) as defined in [HEVC]. 2350 Informative note: This parameter was added primarily to 2351 complement a similar codepoint in the ITU-T Recommendation 2352 H.245, so as to facilitate signaling gateway designs. The 2353 decoded picture buffer stores reconstructed samples. There 2354 is no relationship between the size of the decoded picture 2355 buffer and the buffers used in RTP, especially de- 2356 packetization and de-jitter buffers. 2358 max-br: 2359 The value of max-br is an integer indicating the maximum video 2360 bitrate in units of CpbBrVclFactor bits per second for the VCL 2361 HRD parameters and in units of CpbBrNalFactor bits per second 2362 for the NAL HRD parameters, where CpbBrVclFactor and 2363 CpbBrNalFactor are defined in Section A.4 of [HEVC]. 2365 The max-br parameter signals that the video decoder of the 2366 receiver is capable of decoding video at a higher bitrate than 2367 is required by the highest level. 2369 When max-br is signaled, the video codec of the receiver MUST 2370 be able to decode bitstreams that conform to the highest 2371 level, with the following exceptions in the limits specified 2372 by the highest level: 2374 o The value of max-br replaces the MaxBR value in Table A-2 2375 of [HEVC] for the highest level. 2376 o When the max-cpb parameter is not present, the result of 2377 the following formula replaces the value of MaxCPB in Table 2378 A-1 of [HEVC]: 2380 (MaxCPB of the highest level) * max-br / (MaxBR of the 2381 highest level) 2383 For example, if a receiver signals capability for Main profile 2384 Level 2 with max-br equal to 2000, this indicates a maximum 2385 video bitrate of 2000 kbits/sec for VCL HRD parameters, a 2386 maximum video bitrate of 2200 kbits/sec for NAL HRD 2387 parameters, and a CPB size of 2000000 bits (2000000 / 1500000 2388 * 1500000). 2390 Senders MAY use this knowledge to send higher bitrate video as 2391 allowed in the level definition of Annex A of HEVC to achieve 2392 improved video quality. 2394 When not present, the value of max-br is inferred to be equal 2395 to the value of MaxBR given in Table A-2 of [HEVC] for the 2396 highest level. 2398 The value of max-br MUST be in the range of MaxBR to 2399 16 * MaxBR, inclusive, where MaxBR is given in Table A-2 of 2400 [HEVC] for the highest level. 2402 Informative note: This parameter was added primarily to 2403 complement a similar codepoint in the ITU-T Recommendation 2404 H.245, so as to facilitate signaling gateway designs. The 2405 assumption that the network is capable of handling such 2406 bitrates at any given time cannot be made from the value of 2407 this parameter. In particular, no conclusion can be drawn 2408 that the signaled bitrate is possible under congestion 2409 control constraints. 2411 max-tr: 2412 The value of max-tr is an integer indication the maximum 2413 number of tile rows. The max-tr parameter signals that the 2414 receiver is capable of decoding video with a larger number of 2415 tile rows than the value allowed by the highest level. 2417 When max-tr is signaled, the receiver MUST be able to decode 2418 bitstreams that conform to the highest level, with the 2419 exception that the MaxTileRows value in Table A-1 of [HEVC] 2420 for the highest level is replaced with the value of max-tr. 2422 Senders MAY use this knowledge to send pictures utilizing a 2423 larger number of tile rows than the value allowed by the 2424 highest level. 2426 When not present, the value of max-tr is inferred to be equal 2427 to the value of MaxTileRows given in Table A-1 of [HEVC] for 2428 the highest level. 2430 The value of max-tr MUST be in the range of MaxTileRows to 2431 16 * MaxTileRows, inclusive, where MaxTileRows is given in 2432 Table A-1 of [HEVC] for the highest level. 2434 max-tc: 2435 The value of max-tc is an integer indication the maximum 2436 number of tile columns. The max-tc parameter signals that the 2437 receiver is capable of decoding video with a larger number of 2438 tile columns than the value allowed by the highest level. 2440 When max-tc is signaled, the receiver MUST be able to decode 2441 bitstreams that conform to the highest level, with the 2442 exception that the MaxTileCols value in Table A-1 of [HEVC] 2443 for the highest level is replaced with the value of max-tc. 2445 Senders MAY use this knowledge to send pictures utilizing a 2446 larger number of tile columns than the value allowed by the 2447 highest level. 2449 When not present, the value of max-tc is inferred to be equal 2450 to the value of MaxTileCols given in Table A-1 of [HEVC] for 2451 the highest level. 2453 The value of max-tc MUST be in the range of MaxTileCols to 2454 16 * MaxTileCols, inclusive, where MaxTileCols is given in 2455 Table A-1 of [HEVC] for the highest level. 2457 max-fps: 2459 The value of max-fps is an integer indicating the maximum 2460 picture rate in units of pictures per 100 seconds that can be 2461 effectively processed by the receiver. The max-fps parameter 2462 MAY be used to signal that the receiver has a constraint in 2463 that it is not capable of processing video effectively at the 2464 full picture rate that is implied by the highest level and, 2465 when present, one or more of the parameters max-lsr, max-lps, 2466 and max-br. 2468 The value of max-fps is not necessarily the picture rate at 2469 which the maximum picture size can be sent, it constitutes a 2470 constraint on maximum picture rate for all resolutions. 2472 Informative note: The max-fps parameter is semantically 2473 different from max-lsr, max-lps, max-cpb, max-dpb, max-br, 2474 max-tr, and max-tc in that max-fps is used to signal a 2475 constraint, lowering the maximum picture rate from what is 2476 implied by other parameters. 2478 The encoder SHOULD use a picture rate equal to or less than 2479 this value. An exception is when sending a pre-encoded 2480 bitstream, in which case the picture rate may be greater than 2481 the value of max-fps. In cases where the max-fps parameter is 2482 absent the encoder is free to choose any picture rate 2483 according to the highest level and any signaled optional 2484 parameters. 2486 The value of max-fps MUST be smaller than or equal to the full 2487 picture rate that is implied by the highest level and, when 2488 present, one or more of the parameters max-lsr, max-lps, and 2489 max-br. 2491 sprop-max-don-diff: 2493 The value of this parameter MUST be equal to 0, if the RTP 2494 stream does not depend on other RTP streams and there is no 2495 NAL unit naluA that is followed in transmission order by any 2496 NAL unit preceding naluA in decoding order. Otherwise, this 2497 parameter specifies the maximum absolute difference between 2498 the decoding order number (i.e., AbsDon) values of any two NAL 2499 units naluA and naluB, where naluA follows naluB in decoding 2500 order and precedes naluB in transmission order. 2502 The value of sprop-max-don-diff MUST be an integer in the 2503 range of 0 to 32767, inclusive. 2505 When not present, the value of sprop-max-don-diff is inferred 2506 to be equal to 0. 2508 When the RTP stream depends on one or more other RTP streams 2509 (in this case tx-mode MUST be equal to "MST" and MST is in 2510 use), this parameter MUST be present and the value MUST be 2511 greater than 0. 2513 Informative note: When the RTP stream does not depend on 2514 other RTP streams, either MST or SST may be in use. 2516 sprop-depack-buf-nalus: 2518 This parameter specifies the maximum number of NAL units that 2519 precede a NAL unit in transmission order and follow the NAL 2520 unit in decoding order. 2522 The value of sprop-depack-buf-nalus MUST be an integer in the 2523 range of 0 to 32767, inclusive. 2525 When not present, the value of sprop-depack-buf-nalus is 2526 inferred to be equal to 0. 2528 When the RTP stream depends on one or more other RTP streams 2529 (in this case tx-mode MUST be equal to "MST" and MST is in 2530 use), this parameter MUST be present and the value MUST be 2531 greater than 0. 2533 sprop-depack-buf-bytes: 2535 This parameter signals the required size of the de- 2536 packetization buffer in units of bytes. The value of the 2537 parameter MUST be greater than or equal to the maximum buffer 2538 occupancy (in units of bytes) of the de-packetization buffer 2539 as specified in section 6. 2541 The value of sprop-depack-buf-bytes MUST be an integer in the 2542 range of 0 to 4294967295, inclusive. 2544 When the RTP stream depends on one or more other RTP streams 2545 (in this case tx-mode MUST be equal to "MST" and MST is in 2546 use) or sprop-max-don-diff is present and greater than 0, this 2547 parameter MUST be present and the value MUST be greater than 2548 0. 2550 Informative note: The value of sprop-depack-buf-bytes 2551 indicates the required size of the de-packetization buffer 2552 only. When network jitter can occur, an appropriately 2553 sized jitter buffer has to be available as well. 2555 depack-buf-cap: 2557 This parameter signals the capabilities of a receiver 2558 implementation and indicates the amount of de-packetization 2559 buffer space in units of bytes that the receiver has available 2560 for reconstructing the NAL unit decoding order from NAL units 2561 carried in one or more RTP streams. A receiver is able to 2562 handle any RTP stream, and its dependent RTP streams, when 2563 present, for which the value of the sprop-depack-buf-bytes 2564 parameter is smaller than or equal to this parameter. 2566 When not present, the value of depack-buf-cap is inferred to 2567 be equal to 4294967295. The value of depack-buf-cap MUST be 2568 an integer in the range of 1 to 4294967295, inclusive. 2570 Informative note: depack-buf-cap indicates the maximum 2571 possible size of the de-packetization buffer of the 2572 receiver only. When network jitter can occur, an 2573 appropriately sized jitter buffer has to be available as 2574 well. 2576 sprop-segmentation-id: 2578 This parameter MAY be used to signal the segmentation tools 2579 present in the bitstream and that can be used for 2580 parallelization. The value of sprop-segmentation-id MUST be 2581 an integer in the range of 0 to 3, inclusive. When not 2582 present, the value of sprop-segmentation-id is inferred to be 2583 equal to 0. 2585 When sprop-segmentation-id is equal to 0, no information about 2586 the segmentation tools is provided. When sprop-segmentation- 2587 id is equal to 1, it indicates that slices are present in the 2588 bitstream. When sprop-segmentation-id is equal to 2, it 2589 indicates that tiles are present in the bitstream. When 2590 sprop-segmentation-id is equal to 3, it indicates that WPP is 2591 used in the bitstream. 2593 sprop-spatial-segmentation-idc: 2595 A base16 [RFC4648] representation of the syntax element 2596 min_spatial_segmentation_idc as specified in [HEVC]. This 2597 parameter MAY be used to describe parallelization capabilities 2598 of the bitstream. 2600 dec-parallel-cap: 2602 This parameter MAY be used to indicate the decoder's 2603 additional decoding capabilities given the presence of tools 2604 enabling parallel decoding, such as slices, tiles, and WPP, in 2605 the bitstream. The decoding capability of the decoder may 2606 vary with the setting of the parallel decoding tools present 2607 in the bitstream, e.g. the size of the tiles that are present 2608 in a bitstream. Therefore, multiple capability points may be 2609 provided, each indicating the minimum required decoding 2610 capability that is associated with a parallelism requirement, 2611 which is a requirement on the bitstream that enables parallel 2612 decoding. 2614 Each capability point is defined as a combination of 1) a 2615 parallelism requirement, 2) a profile (determined by profile- 2616 space and profile-id), 3) a highest level, and 4) a maximum 2617 processing rate, a maximum picture size, and a maximum video 2618 bitrate that may be equal to or greater than that determined 2619 by the highest level. The parameter's syntax in ABNF 2620 [RFC5234] is as follows: 2622 dec-parallel-cap = "dec-parallel-cap={" cap-point *("," 2623 cap-point) "}" 2625 cap-point = ("w" / "t") ":" spatial-seg-idc 1*(";" 2626 cap-parameter) 2628 spatial-seg-idc = 1*4DIGIT ; (1-4095) 2630 cap-parameter = tier-flag / level-id / max-lsr 2631 / max-lps / max-br 2633 tier-flag = "tier-flag" EQ ("0" / "1") 2635 level-id = "level-id" EQ 1*3DIGIT ; (0-255) 2637 max-lsr = "max-lsr" EQ 1*20DIGIT ; (0- 2638 18,446,744,073,709,551,615) 2640 max-lps = "max-lps" EQ 1*10DIGIT ; (0-4,294,967,295) 2642 max-br = "max-br" EQ 1*20DIGIT ; (0- 2643 18,446,744,073,709,551,615) 2645 EQ = "=" 2647 The set of capability points expressed by the dec-parallel-cap 2648 parameter is enclosed in a pair of curly braces ("{}"). Each 2649 set of two consecutive capability points is separated by a 2650 comma (','). Within each capability point, each set of two 2651 consecutive parameters, and when present, their values, is 2652 separated by a semicolon (';'). 2654 The profile of all capability points is determined by profile- 2655 space and profile-id that are outside the dec-parallel-cap 2656 parameter. 2658 Each capability point starts with an indication of the 2659 parallelism requirement, which consists of a parallel tool 2660 type, which may be equal to 'w' or 't', and a decimal value of 2661 the spatial-seg-idc parameter. When the type is 'w', the 2662 capability point is valid only for H.265 bitstreams with WPP 2663 in use, i.e. entropy_coding_sync_enabled_flag equal to 1. 2664 When the type is 't', the capability point is valid only for 2665 H.265 bitstreams with WPP not in use (i.e. 2666 entropy_coding_sync_enabled_flag equal to 0). The capability- 2667 point is valid only for H.265 bitstreams with 2668 min_spatial_segmentation_idc equal to or greater than spatial- 2669 seg-idc. 2671 After the parallelism requirement indication, each capability 2672 point continues with one or more pairs of parameter and value 2673 in any order for any of the following parameters: 2675 o tier-flag 2676 o level-id 2677 o max-lsr 2678 o max-lps 2679 o max-br 2681 At most one occurrence of each of the above five parameters is 2682 allowed within each capability point. 2684 The values of dec-parallel-cap.tier-flag and dec-parallel- 2685 cap.level-id for a capability point indicate the highest level 2686 of the capability point. The values of dec-parallel-cap.max- 2687 lsr, dec-parallel-cap.max-lps, and dec-parallel-cap.max-br for 2688 a capability point indicate the maximum processing rate in 2689 units of luma samples per second, the maximum picture size in 2690 units of luma samples, and the maximum video bitrate (in units 2691 of CpbBrVclFactor bits per second for the VCL HRD parameters 2692 and in units of CpbBrNalFactor bits per second for the NAL HRD 2693 parameters where CpbBrVclFactor and CpbBrNalFactor are defined 2694 in Section A.4 of [HEVC]). 2696 When not present, the value of dec-parallel-cap.tier-flag is 2697 inferred to be equal to the value of tier-flag outside the 2698 dec-parallel-cap parameter. When not present, the value of 2699 dec-parallel-cap.level-id is inferred to be equal to the value 2700 of max-recv-level-id outside the dec-parallel-cap parameter. 2701 When not present, the value of dec-parallel-cap.max-lsr, dec- 2702 parallel-cap.max-lps, or dec-parallel-cap.max-br is inferred 2703 to be equal to the value of max-lsr, max-lps, or max-br, 2704 respectively, outside the dec-parallel-cap parameter. 2706 The general decoding capability, expressed by the set of 2707 parameters outside of dec-parallel-cap, is defined as the 2708 capability point that is determined by the following 2709 combination of parameters: 1) the parallelism requirement 2710 corresponding to the value of sprop-segmentation-id equal to 0 2711 for a bitstream, 2) the profile determined by profile-space 2712 and profile-id, 3) the highest level determined by tier-flag 2713 and max-recv-level-id, and 4) the maximum processing rate, the 2714 maximum picture size, and the maximum video bitrate determined 2715 by the highest level. The general decoding capability MUST 2716 NOT be included as one of the set of capability points in the 2717 dec-parallel-cap parameter. 2719 For example, the following parameters express the general 2720 decoding capability of 720p30 (Level 3.1) plus an additional 2721 decoding capability of 1080p30 (Level 4) given that the 2722 spatially largest tile or slice used in the bitstream is equal 2723 to or less than 1/3 of the picture size: 2725 a=fmtp:98 level-id=93;dec-parallel-cap={t:8;level-id=120} 2727 For another example, the following parameters express an 2728 additional decoding capability of 1080p30, using dec-parallel- 2729 cap.max-lsr and dec-parallel-cap.max-lps, given that WPP is 2730 used in the bitstream: 2732 a=fmtp:98 level-id=93;dec-parallel-cap={w:8; 2733 max-lsr=62668800;max-lps=2088960} 2735 Informative note: When min_spatial_segmentation_idc is 2736 present in a bitstream and WPP is not used, [HEVC] 2737 specifies that there is no slice or no tile in the 2738 bitstream containing more than 4 * PicSizeInSamplesY / 2739 ( min_spatial_segmentation_idc + 4 ) luma samples. 2741 Encoding considerations: 2743 This type is only defined for transfer via RTP (RFC 3550). 2745 Security considerations: 2747 See Section 9 of RFC XXXX. 2749 Public specification: 2751 Please refer to Section 13 of RFC XXXX. 2753 Additional information: None 2755 File extensions: none 2757 Macintosh file type code: none 2759 Object identifier or OID: none 2761 Person & email address to contact for further information: 2763 Intended usage: COMMON 2765 Author: See Section 14 of RFC XXXX. 2767 Change controller: 2769 IETF Audio/Video Transport Payloads working group delegated 2770 from the IESG. 2772 7.2 SDP Parameters 2774 The receiver MUST ignore any parameter unspecified in this memo. 2776 7.2.1 Mapping of Payload Type Parameters to SDP 2778 The media type video/H265 string is mapped to fields in the Session 2779 Description Protocol (SDP) [RFC4566] as follows: 2781 o The media name in the "m=" line of SDP MUST be video. 2783 o The encoding name in the "a=rtpmap" line of SDP MUST be H265 (the 2784 media subtype). 2786 o The clock rate in the "a=rtpmap" line MUST be 90000. 2788 o The OPTIONAL parameters "profile-space", "profile-id", "tier- 2789 flag", "level-id", "interop-constraints", "profile-compatibility- 2790 indicator", "sprop-sub-layer-id", "recv-sub-layer-id", "max-recv- 2791 level-id", "tx-mode", "max-lsr", "max-lps", "max-cpb", "max-dpb", 2792 "max-br", "max-tr", "max-tc", "max-fps", "sprop-max-don-diff", 2793 "sprop-depack-buf-nalus", "sprop-depack-buf-bytes", "depack-buf- 2794 cap", "sprop-segmentation-id", "sprop-spatial-segmentation-idc", 2795 and "dec-parallel-cap", when present, MUST be included in the 2796 "a=fmtp" line of SDP. This parameter is expressed as a media 2797 type string, in the form of a semicolon separated list of 2798 parameter=value pairs. 2800 o The OPTIONAL parameters "sprop-vps", "sprop-sps", and "sprop- 2801 pps", when present, MUST be included in the "a=fmtp" line of SDP 2802 or conveyed using the "fmtp" source attribute as specified in 2803 section 6.3 of [RFC5576]. For a particular media format (i.e. 2804 RTP payload type), "sprop-vps" "sprop-sps", or "sprop-pps" MUST 2805 NOT be both included in the "a=fmtp" line of SDP and conveyed 2806 using the "fmtp" source attribute. When included in the "a=fmtp" 2807 line of SDP, these parameters are expressed as a media type 2808 string, in the form of a semicolon separated list of 2809 parameter=value pairs. When conveyed using the "fmtp" source 2810 attribute, these parameters are only associated with the given 2811 source and payload type as parts of the "fmtp" source attribute. 2813 Informative note: Conveyance of "sprop-vps", "sprop-sps", and 2814 "sprop-pps" using the "fmtp" source attribute allows for out- 2815 of-band transport of parameter sets in topologies like Topo- 2816 Video-switch-MCU as specified in [RFC5117]. 2818 An example of media representation in SDP is as follows: 2820 m=video 49170 RTP/AVP 98 2821 a=rtpmap:98 H265/90000 2822 a=fmtp:98 profile-id=1; 2823 sprop-vps=