Advanced Video Coding (AVC), also referred to as H.264 or MPEG-4 Part 10, is a video compression standard based on block-oriented, motion-compensated coding. It is by far the most commonly used format for the recording, compression, and distribution of video content, used by 79% of video industry developers . It supports a maximum resolution of 8K UHD.
H.264 was standardized by the ITU-T Video Coding Experts Group (VCEG) of Study Group 16 together with the ISO/IEC JTC 1 Moving Picture Experts Group (MPEG). The project partnership effort is known as the Joint Video Team (JVT). The ITU-T H.264 standard and the ISO/IEC MPEG-4 AVC standard (formally, ISO/IEC 14496-10 – MPEG-4 Part 10, Advanced Video Coding) are jointly maintained so that they have identical technical content. The final drafting work on the first version of the standard was completed in May 2003, and various extensions of its capabilities have been added in subsequent editions. High Efficiency Video Coding (HEVC), a.k.a. H.265 and MPEG-H Part 2 is a successor to H.264/MPEG-4 AVC developed by the same organizations, while earlier standards are still in common use.
H.264 is perhaps best known as being the most commonly used video encoding format on Blu-ray Discs. It has also been widely used by streaming Internet sources, such as videos from Netflix, Hulu, Amazon Prime Video, Vimeo, YouTube (more recently transitioning to VP9 and AV1) and the iTunes Store, Web software such as the Adobe Flash Player and Microsoft Silverlight, and also various HDTV broadcasts over terrestrial (ATSC, ISDB-T, DVB-T or DVB-T2), cable (DVB-C), and satellite (DVB-S and DVB-S2) systems.
H.264 is restricted by patents owned by various parties. A license covering most (but not all) patents essential to H.264 is administered by a patent pool formerly administered by MPEG LA. Via Licensing Corp acquired MPEG LA in April 2023 and formed a new patent pool administration company called Via Licensing Alliance. The commercial use of patented H.264 technologies requires the payment of royalties to Via and other patent owners. MPEG LA has allowed the free use of H.264 technologies for streaming Internet video that is free to end users, and Cisco paid royalties to MPEG LA on behalf of the users of binaries for its open source H.264 encoder openH264.
Naming The H.264 name follows the ITU-T naming convention, where Recommendations are given a letter corresponding to their series and a recommendation number within the series. H.264 is part of "H-Series Recommendations: Audiovisual and multimedia systems". H.264 is further categorized into "H.200-H.499: Infrastructure of audiovisual services" and "H.260-H.279: Coding of moving video". The MPEG-4 AVC name relates to the naming convention in ISO/IEC MPEG, where the standard is part 10 of ISO/IEC 14496, which is the suite of standards known as MPEG-4. The standard was developed jointly in a partnership of VCEG and MPEG, after earlier development work in the ITU-T as a VCEG project called H.26L. It is thus common to refer to the standard with names such as H.264/AVC, AVC/H.264, H.264/MPEG-4 AVC, or MPEG-4/H.264 AVC, to emphasize the common heritage. Occasionally, it is also referred to as "the JVT codec", in reference to the Joint Video Team (JVT) organization that developed it. (Such partnership and multiple naming is not uncommon. For example, the video compression standard known as MPEG-2 also arose from the partnership between MPEG and the ITU-T, where MPEG-2 video is known to the ITU-T community as H.262.) Some software programs (such as VLC media player) internally identify this standard as AVC1.
History Overall history In early 1998, the Video Coding Experts Group (VCEG – 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 (Microsoft, formerly PictureTel, U.S.). The first draft design for that new standard was adopted in August 1999. In 2000, Thomas Wiegand (Heinrich Hertz Institute, Germany) became VCEG co-chair.
In December 2001, VCEG and the Moving Picture Experts Group (MPEG – ISO/IEC JTC 1/SC 29/WG 11) formed a Joint Video Team (JVT), with the charter to finalize the video coding standard.Joint Video Team, ITU-T Web site. Formal approval of the specification came in March 2003. The JVT was (is) chaired by Gary Sullivan, Thomas Wiegand, and Ajay Luthra (Motorola, U.S.: later 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 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 Y′CBCR 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 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 access units 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 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 maps 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 29 completed revisions, corrigenda, and amendments.
Applications
The H.264 video format has a very broad application range that covers all forms of digital compressed video from low bit-rate Internet streaming applications to HDTV broadcast and Digital Cinema applications with nearly lossless coding. With the use of H.264, bit rate savings of 50% or more compared to MPEG-2 Part 2 are reported. For example, H.264 has been reported to give the same Digital Satellite TV quality as current MPEG-2 implementations with less than half the bitrate, with current MPEG-2 implementations working at around 3.5 Mbit/s and H.264 at only 1.5 Mbit/s. Sony claims that 9 Mbit/s AVC recording mode is equivalent to the image quality of the HDV format, which uses approximately 18–25 Mbit/s.
To ensure compatibility and problem-free adoption of H.264/AVC, many standards bodies have amended or added to their video-related standards so that users of these standards can employ H.264/AVC. Both the Blu-ray Disc format and the now-discontinued HD DVD format include the H.264/AVC High Profile as one of three mandatory video compression formats. The Digital Video Broadcast project (DVB) approved the use of H.264/AVC for broadcast television in late 2004.
The Advanced Television Systems Committee (ATSC) standards body in the United States approved the use of H.264/AVC for broadcast television in July 2008. It has also been approved for use with the more recent ATSC-M/H (Mobile/Handheld) standard, using the AVC and SVC portions of H.264.
The closed-circuit-television and video-surveillance markets have included the technology in many products.
Many common DSLRs use H.264 video wrapped in QuickTime MOV containers as the native recording format.
Derived formats AVCHD is a high-definition recording format designed by Sony and Panasonic that uses H.264 (conforming to H.264 while adding additional application-specific features and constraints).
AVC-Intra is an intraframe-only compression format, developed by Panasonic.