Editing Advanced Video Coding (section)

== History ==
=== Overall history ===
In early 1998, the [[Video Coding Experts Group]] (VCEG&nbsp;– ITU-T SG16 Q.6) issued a call for proposals on a project called H.26L, with the target to double the coding efficiency (which means halving the bit rate necessary for a given level of fidelity) in comparison to any other existing video coding standards for a broad variety of applications. [[VCEG]] was chaired by [[Gary Sullivan (engineer)|Gary Sullivan]] ([[Microsoft]], formerly [[PictureTel]], U.S.). The first draft design for that new standard was adopted in August 1999. In 2000, [[Thomas Wiegand]] ([[Fraunhofer Institute for Telecommunications|Heinrich Hertz Institute]], Germany) became VCEG co-chair.

In December 2001, VCEG and the Moving Picture Experts Group ([[MPEG]]&nbsp;– [[ISO/IEC JTC 1/SC 29]]/WG 11) formed a Joint Video Team (JVT), with the charter to finalize the video coding standard.<ref name=JVTsite>[http://www.itu.int/en/ITU-T/studygroups/com16/video/Pages/jvt.aspx Joint Video Team], [[ITU-T]] Web site.</ref> Formal approval of the specification came in March 2003. The JVT was (is) chaired by [[Gary Sullivan (engineer)|Gary Sullivan]], [[Thomas Wiegand]], and Ajay Luthra ([[Motorola]], U.S.: later [[Arris Group|Arris]], U.S.). In July 2004, the Fidelity Range Extensions (FRExt) project was finalized. From January 2005 to November 2007, the JVT was working on an extension of H.264/AVC towards scalability by an Annex (G) called [[Scalable Video Coding]] (SVC). The JVT management team was extended by [[Jens-Rainer Ohm]] ([[RWTH Aachen University]], Germany). From July 2006 to November 2009, the JVT worked on [[Multiview Video Coding]] (MVC), an extension of H.264/AVC towards [[3D television]] and limited-range [[free-viewpoint television]]. That work included the development of two new profiles of the standard: the Multiview High Profile and the Stereo High Profile.

Throughout the development of the standard, additional messages for containing supplemental enhancement information (SEI) have been developed. SEI messages can contain various types of data that indicate the timing of the video pictures or describe various properties of the coded video or how it can be used or enhanced. SEI messages are also defined that can contain arbitrary user-defined data. SEI messages do not affect the core decoding process, but can indicate how the video is recommended to be post-processed or displayed. Some other high-level properties of the video content are conveyed in video usability information (VUI), such as the indication of the [[color space]] for interpretation of the video content. As new color spaces have been developed, such as for [[High-dynamic-range video|high dynamic range]] and [[wide color gamut]] video, additional VUI identifiers have been added to indicate them.

=== Fidelity range extensions and professional profiles ===
The standardization of the first version of H.264/AVC was completed in May 2003. In the first project to extend the original standard, the JVT then developed what was called the Fidelity Range Extensions (FRExt). These extensions enabled higher quality video coding by supporting increased sample bit depth precision and higher-resolution color information, including the sampling structures known as [[YCbCr|Y′C<sub>B</sub>C<sub>R</sub>]] 4:2:2 (a.k.a. [[YUV 4:2:2]]) and 4:4:4. Several other features were also included in the FRExt project, such as adding an 8×8 integer [[discrete cosine transform]] (integer DCT) with adaptive switching between the 4×4 and 8×8 transforms, encoder-specified perceptual-based quantization weighting matrices, efficient inter-picture lossless coding, and support of additional color spaces. The design work on the FRExt project was completed in July 2004, and the drafting work on them was completed in September 2004.

Five other new profiles (see version 7 below) intended primarily for professional applications were then developed, adding extended-gamut color space support, defining additional aspect ratio indicators, defining two additional types of "supplemental enhancement information" (post-filter hint and tone mapping), and deprecating one of the prior FRExt profiles (the High 4:4:4 profile) that industry feedback{{By whom|date=December 2016}} indicated should have been designed differently.

=== Scalable video coding ===
The next major feature added to the standard was [[Scalable Video Coding]] (SVC). Specified in Annex G of H.264/AVC, SVC allows the construction of bitstreams that contain ''layers'' of sub-bitstreams that also conform to the standard, including one such bitstream known as the "base layer" that can be decoded by a H.264/AVC [[codec]] that does not support SVC. For temporal bitstream scalability (i.e., the presence of a sub-bitstream with a smaller temporal sampling rate than the main bitstream), complete [[Network Abstraction Layer#Access Units|access unit]]s are removed from the bitstream when deriving the sub-bitstream. In this case, high-level syntax and inter-prediction reference pictures in the bitstream are constructed accordingly. On the other hand, for spatial and quality bitstream scalability (i.e. the presence of a sub-bitstream with lower spatial resolution/quality than the main bitstream), the NAL ([[Network Abstraction Layer]]) is removed from the bitstream when deriving the sub-bitstream. In this case, inter-layer prediction (i.e., the prediction of the higher spatial resolution/quality signal from the data of the lower spatial resolution/quality signal) is typically used for efficient coding. The [[Scalable Video Coding]] extensions were completed in November 2007.

=== Multiview video coding ===
The next major feature added to the standard was [[Multiview Video Coding]] (MVC). Specified in Annex H of H.264/AVC, MVC enables the construction of bitstreams that represent more than one view of a video scene. An important example of this functionality is [[stereoscopy|stereoscopic 3D]] video coding. Two profiles were developed in the MVC work: Multiview High profile supports an arbitrary number of views, and Stereo High profile is designed specifically for two-view stereoscopic video. The Multiview Video Coding extensions were completed in November 2009.

=== 3D-AVC and MFC stereoscopic coding ===
Additional extensions were later developed that included 3D video coding with joint coding of [[depth map]]s and texture (termed 3D-AVC), multi-resolution frame-compatible (MFC) stereoscopic and 3D-MFC coding, various additional combinations of features, and higher frame sizes and frame rates.

=== Versions ===
Versions of the H.264/AVC standard include the following completed revisions, corrigenda, and amendments (dates are final approval dates in ITU-T, while final "International Standard" approval dates in ISO/IEC are somewhat different and slightly later in most cases). Each version represents changes relative to the next lower version that is integrated into the text.

* Version 1 (Edition 1): (May 30, 2003) First approved version of H.264/AVC containing Baseline, Main, and Extended profiles.<ref name=AVCV1March2003ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (05/2003) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=6312 |date=2003-05-30 |access-date=2013-04-18}}</ref>
* Version 2 (Edition 1.1): (May 7, 2004) Corrigendum containing various minor corrections.<ref name=AVCV1CorMay2004ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (05/2003) Cor. 1 (05/2004) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=7255 |date=2004-05-07 |access-date=2013-04-18}}</ref>
* Version 3 (Edition 2): (March 1, 2005) Major addition containing the first amendment, establishing the Fidelity Range Extensions (FRExt). This version added the High, High 10, High 4:2:2, and High 4:4:4 profiles.<ref name=AVCV2March2005ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (03/2005) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=7825 |date=2005-03-01 |access-date=2013-04-18}}</ref> After a few years, the High profile became the most commonly used profile of the standard.
* Version 4 (Edition 2.1): (September 13, 2005) Corrigendum containing various minor corrections and adding three aspect ratio indicators.<ref name=AVCV2September2005ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (2005) Cor. 1 (09/2005) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=8572 |date=2005-09-13 |access-date=2013-04-18}}</ref>
* Version 5 (Edition 2.2): (June 13, 2006) Amendment consisting of removal of prior High 4:4:4 profile (processed as a corrigendum in ISO/IEC).<ref name=AVCV2June2006ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (2005) Amd. 1 (06/2006) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=8811 |date=2006-06-13 |access-date=2013-04-18}}</ref>
* Version 6 (Edition 2.2): (June 13, 2006) Amendment consisting of minor extensions like extended-gamut color space support (bundled with above-mentioned aspect ratio indicators in ISO/IEC).<ref name=AVCV2June2006ITURecommendations/>
* Version 7 (Edition 2.3): (April 6, 2007) Amendment containing the addition of the High 4:4:4 Predictive profile and four Intra-only profiles (High 10 Intra, High 4:2:2 Intra, High 4:4:4 Intra, and CAVLC 4:4:4 Intra).<ref name=AVCV2April2007ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (2005) Amd. 2 (04/2007) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=9036 |date=2007-04-06 |access-date=2013-04-18}}</ref>
* Version 8 (Edition 3): (November 22, 2007) Major addition to H.264/AVC containing the amendment for [[Scalable Video Coding]] (SVC) containing Scalable Baseline, Scalable High, and Scalable High Intra profiles.<ref name=AVCV3November2007ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (11/2007) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=9226 |date=2007-11-22 |access-date=2013-04-18}}</ref>
* Version 9 (Edition 3.1): (January 13, 2009) Corrigendum containing minor corrections.<ref name=AVCV3January2009ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (2007) Cor. 1 (01/2009) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=9519 |date=2009-01-13 |access-date=2013-04-18}}</ref>
* Version 10 (Edition 4): (March 16, 2009) Amendment containing definition of a new profile (the Constrained Baseline profile) with only the common subset of capabilities supported in various previously specified profiles.<ref name=AVCV4March2009ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (03/2009) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=9710 |date=2009-03-16 |access-date=2013-04-18}}</ref>
* Version 11 (Edition 4): (March 16, 2009) Major addition to H.264/AVC containing the amendment for [[Multiview Video Coding]] (MVC) extension, including the Multiview High profile.<ref name=AVCV4March2009ITURecommendations/>
* Version 12 (Edition 5): (March 9, 2010) Amendment containing definition of a new MVC profile (the Stereo High profile) for two-view video coding with support of interlaced coding tools and specifying an additional supplemental enhancement information (SEI) message termed the frame packing arrangement SEI message.<ref name=AVCV5March2010ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (03/2010) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=10635 |date=2010-03-09 |access-date=2013-04-18}}</ref>
* Version 13 (Edition 5): (March 9, 2010) Corrigendum containing minor corrections.<ref name=AVCV5March2010ITURecommendations/>
* Version 14 (Edition 6): (June 29, 2011) Amendment specifying a new level (Level 5.2) supporting higher processing rates in terms of maximum macroblocks per second, and a new profile (the Progressive High profile) supporting only the frame coding tools of the previously specified High profile.<ref name=AVCV6June2011ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (06/2011) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=11293 |date=2011-06-29 |access-date=2013-04-18}}</ref>
* Version 15 (Edition 6): (June 29, 2011) Corrigendum containing minor corrections.<ref name=AVCV6June2011ITURecommendations/>
* Version 16 (Edition 7): (January 13, 2012) Amendment containing definition of three new profiles intended primarily for real-time communication applications: the Constrained High, Scalable Constrained Baseline, and Scalable Constrained High profiles.<ref name=AVCV7January2012ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (01/2012) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=11466 |date=2012-01-13 |access-date=2013-04-18}}</ref>
* Version 17 (Edition 8): (April 13, 2013) Amendment with additional SEI message indicators.<ref name=AVC8June2013ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (04/2013) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=11830 |date=2013-06-12 |access-date=2013-06-16}}</ref>
* Version 18 (Edition 8): (April 13, 2013) Amendment to specify the coding of depth map data for 3D stereoscopic video, including a Multiview Depth High profile.<ref name=AVC8June2013ITURecommendations/>
* Version 19 (Edition 8): (April 13, 2013) Corrigendum to correct an error in the sub-bitstream extraction process for multiview video.<ref name=AVC8June2013ITURecommendations/>
* Version 20 (Edition 8): (April 13, 2013) Amendment to specify additional [[color space]] identifiers (including support of [[Rec. 2020|ITU-R Recommendation BT.2020]] for [[Ultra-high-definition television|UHDTV]]) and an additional model type in the tone mapping information SEI message.<ref name=AVC8June2013ITURecommendations/>
* Version 21 (Edition 9): (February 13, 2014) Amendment to specify the Enhanced Multiview Depth High profile.<ref name=AVC9February2014ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (02/2014) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=12063 |date=2014-11-28 |access-date=2016-02-28}}</ref>
* Version 22 (Edition 9): (February 13, 2014) Amendment to specify the multi-resolution frame compatible (MFC) enhancement for 3D stereoscopic video, the MFC High profile, and minor corrections.<ref name=AVC9February2014ITURecommendations/>
* Version 23 (Edition 10): (February 13, 2016) Amendment to specify MFC stereoscopic video with depth maps, the MFC Depth High profile, the mastering display color volume SEI message, and additional color-related VUI codepoint identifiers.<ref name=AVC13February2016ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (02/2016) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=12641 |date=2016-02-13 |access-date=2017-06-14}}</ref>
* Version 24 (Edition 11): (October 14, 2016) Amendment to specify additional levels of decoder capability supporting larger picture sizes (Levels 6, 6.1, and 6.2), the green metadata SEI message, the alternative depth information SEI message, and additional color-related VUI codepoint identifiers.<ref name=AVC14October2016ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (10/2016) |publisher=ITU |url=http://www.itu.int/ITU-T/recommendations/rec.aspx?rec=12904 |date=2016-10-14 |access-date=2017-06-14}}</ref>
* Version 25 (Edition 12): (April 13, 2017) Amendment to specify the Progressive High 10 profile, [[hybrid log–gamma]] (HLG), and additional color-related VUI code points and SEI messages.<ref name=AVC13April2017ITURecommendations>{{cite news |title=ITU-T Recommendation H.264 (04/2017) |publisher=ITU |url=https://www.itu.int/ITU-T/recommendations/rec.aspx?rec=13189 |date=2017-04-13 |access-date=2017-06-14 |at=See Tables A-1, A-6 and A-7 for the tabulated level-dependent capabilities.}}</ref>
* Version 26 (Edition 13): (June 13, 2019) Amendment to specify additional SEI messages for ambient viewing environment, content light level information, content color volume, equirectangular projection, cubemap projection, sphere rotation, region-wise packing, omnidirectional viewport, SEI manifest, and SEI prefix.<ref>{{Cite web|date=June 13, 2019|title=H.264: Advanced video coding for generic audiovisual services - Version 26 (Edition 13)|url=https://handle.itu.int/11.1002/1000/13903|url-status=live|archive-url=https://web.archive.org/web/20211104102930/https://www.itu.int/ITU-T/recommendations/rec.aspx?rec=13903&lang=en|archive-date=2021-11-04|access-date=2021-11-03|website=www.itu.int}}</ref>
*Version 27 (Edition 14): (August 22, 2021) Amendment to specify additional SEI messages for annotated regions and shutter interval information, and miscellaneous minor corrections and clarifications.<ref>{{Cite web|date=August 22, 2021|title=H.264: Advanced video coding for generic audiovisual services - Version 27 (Edition 14)|url=https://handle.itu.int/11.1002/1000/14659|url-status=live|archive-url=https://web.archive.org/web/20211104103832/https://www.itu.int/ITU-T/recommendations/rec.aspx?rec=14659&lang=en|archive-date=2021-11-04|access-date=2021-11-03|website=www.itu.int}}</ref>
*Version 28 (Edition 15): (August 13, 2024) Amendment to specify additional SEI messages for neural-network postfilter characteristics, neural-network post-filter activation, and phase indication, additional colour type identifiers, and miscellaneous minor corrections and clarifications.<ref>{{Cite web|date=August 13, 2024|title=H.264: Advanced video coding for generic audiovisual services - Version 28 (Edition 15)|url=https://handle.itu.int/11.1002/1000/15935|access-date=2025-02-12|website=www.itu.int}}</ref>