Advanced Video Coding: Difference between revisions

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'''H.264''' is a high compression [[digital video]] [[codec]] standard written by the [[ITU-T]] Video Coding Experts Group (VCEG) together with the ISO/IEC Moving Picture Experts Group (MPEG) as the product of a collective effort known as the Joint Video Team (JVT). This standard is identical to [[ISO]] [[MPEG-4]] part 10, also known as '''AVC''', for Advanced Video Coding. The final drafting work on the first version of the standard was completed in May of 2003.

H.264 is a name related to the [[ITU-T]] line of H.26x video standards, while AVC relates to its [[ISO]]/IEC MPEG roots. It is usual to call the standard as H.264/AVC, or AVC/H.264 to emphasize the common heritage. The name H.26L, also related to its [[ITU-T]] history, is far less common, but still used. Occassionally, it has also been referred to as "the JVT codec", in reference to the organization that developed it.

H.26L, also related to its [[ITU-T]] history, is far less common, but still used.

The intent of H.264/AVC project has been to create a standard that would lead to good video quality at bit rates that are substantially lower (e.g., half or less) that what previous standards would need (e.g., relative to [[MPEG-2]], [[H.263]], or [[MPEG-4]] part 2), and to do so without so much of an increase in complexity as to make the design impractically expensive to implement. An additional goal was to do this in a flexible way that would allow the standard to be applied to a very wide variety of applications (e.g., for both low and high bit rates and low and high resolution video) and to work well on a very wide variety of networks and systems (e.g., for broadcast, DVD storage, RTP/IP packet networks, and ITU-T multimedia telephony systems).

More recently, the JVT has been working on a corrigendum (a list of errata corrections) to the original standard. The drafting work on the corrigendum should be completed in May of 2004.

Since the completion of the original version of the standard in May of 2003, the JVT has done one round of "corrigendum" errata corrections and has developed a set of enhanced-functionality extensions called the "Fidelity Range Extensions" (FRExt). An additional round of corrigendum work is now nearing completion and should be finished in early 2005.

The intents of H.264/AVC project were to create a standard that would lead to fast implementations and bitrates that are half of [[H.263]] rates for the same perceived video quality. That is: implementations that would demand little from the decoder hardware and from the network bandwidth.

H.264/AVC contains several new features that allow it to compress video much more effectively than older codecs. CABAC (Context-Adaptive Binary Arithmetic Coding) is a clever technique that can be used in H.264 to losslessly compress syntax elements in the video stream. H.264 also implements an in-loop deblocking filter which helps prevent the ringing and blocking artifacts common to other [[DCT]]-based image compression techniques. InH.264/AVC previousdefines videoa standards,way to perform [[motion compensation]] isusing handledpreviously-encoded bypictures allowingas blocksreferences in a framemuch tomore referflexible onlyway tothan thein framepast beforestandards it.-- H.264/AVCallowing allowsup framesto 32 reference pictures to be predictedused fromin othersome framescases that(unlike arein arbitrarilyprior farstandards, inwhere the pastlimit was typically 1 or 2). This particular feature usually allows modest improvements in bitrate and quality in most scenes. But (for example) in certain types of scenes with rapid repetitive flashing, it allows a massive reduction in bitrate. These ideas, along with many other new ideas, help H.264 to perform significantly better than MPEG-4any prior ASPstandard can. H.264 can usually perform radically better than [[MPEG-2]] at-- aobtaining fractionthe same quality at half of the bitrate or less.

In addition, theThe JVT isrecently nearing completion ofcompleted the development of some extensions to the original standard that are known as the Fidelity Range Extensions (FRExt). These extensions will support higher-fidelity video coding by supporting increased sample accuracy (including 10-bit and 12-bit coding) and higher-resolution color information (including sampling structures known as [[YUV 4:2:2]] and [[YUV 4:4:4]]). Several other features are also included in the Fidelity Range Extensions project. The drafting work on the Fidelity Range Extensions should bewas completed in the SummerSeptember of 2004.

H.264/AVC is already widely used for videoconferencing, including its support in products of the two main companies in that market (Polycom and Tandberg). It has also been preliminarily adopted as a mandatory part of both of the major rival formats for future enhanced DVD specificationuses, which are known as the HD-DVD, nowand underBlu-Ray developmentDisc byformats. The Digital Video Broadcast ([[DVB]]) organization in Europe has recently approved the DVDuse of H.264/AVC for European broadcast Forumtelevision. A number of broadcasters in Japan and Korea have announced future support for the codec, and it is under consideration for other broadcast use -- for example, it is under consideration in the United States' Advanced Television Systems Committee ([[ATSC]]) and in Europe's Digital Video Broadcast ([[DVB]]) standards bodiesbody. In the wireless world, it ishas underbeen considerationadoped foras adoptionpart byof design release 6 of the 3rd-Generation Partnership Project (3GPP).

As of the time of this writing (late 2004), four companies are producing sample custom chips capable of decoding H.264/AVC video (specifically, Broadcom, Conexant, Sigma Designs, and ST Micro). Such chips will allow widespread deployment of low-cost devices capable of playing H.264/AVC video at standard-definition and high-definition television resolutions.

Like many [[ISO]] video standards, H.264/AVC has a reference implementation that can be freely downloaded. Its main concern is to give examples of H.264/AVC features, instead of being a useful application ''per se''.

Like many [[ISO]]/IEC video standards, H.264/AVC has a reference implementation that can be freely downloaded. Its main concern is to give examples of H.264/AVC features, instead of being a useful application ''per se''.

A tweaked variant of this codec is implemented in the form of the [[Sorenson codec]], as was found by an [[FFmpeg]] developer working on [[reverse-engineering]] the Sorenson codec.