H.264/MPEG-4 AVC

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into Russian: H.264/MPEG-4 AVC. 7% translated in draft.
Submitted for translation by Atreides 19.06.2010

Text

MPEG-4 is a suite of standards which has many "parts", where each part standardizes various entities related to multimedia, such as audio, video, and file formats. To learn more about various parts and what they mean, please see the entry for MPEG-4.

H.264/AVC/MPEG-4 Part 10 (Advanced Video Coding) is a standard for video compression. The final drafting work on the first version of the standard was completed in May 2003.

H.264/AVC is the latest block-oriented motion-compensation-based codec standard developed by the ITU-T Video Coding Experts Group (VCEG) together with the ISO/IEC Moving Picture Experts Group (MPEG), and it was the product of a partnership effort 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. H.264 is used in such applications as Blu-ray Disc, videos from YouTube and the iTunes Store, DVB broadcast, direct-broadcast satellite television service, cable television services, and real-time videoconferencing.Содержание [убрать]

1 Overview

2 Standardization committee and history

3 Applications

4 Patent licensing

4.1 Patents and GNU Free Software licenses

5 Features

6 Profiles

7 Levels

8 Decoded picture buffering

9 Versions

10 Software encoder feature comparison

11 Hardware encoder and IP

12 See also

13 Notes

14 References

15 External links

15.1 Introduction

15.2 The standard

15.3 Reference encoder/decoder

15.4 Standardization committee documents

15.5 Miscellaneous

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Overview

The intent of the H.264/AVC project was to create a standard capable of providing good video quality at substantially lower bit rates than previous standards (e.g. half or less the bit rate of MPEG-2, H.263, or MPEG-4 Part 2), without increasing the complexity of design so much that it would be impractical or excessively expensive to implement. An additional goal was to provide enough flexibility to allow the standard to be applied to a wide variety of applications on a wide variety of networks and systems, including low and high bit rates, low and high resolution video, broadcast, DVD storage, RTP/IP packet networks, and ITU-T multimedia telephony systems.

The H.264 standard is a "family of standards", the members of which are the profiles described below. A specific decoder decodes at least one, but not necessarily all profiles. The decoder specification describes which of the profiles can be decoded.

The standardization of the first version of H.264/AVC was completed in May 2003. The JVT then developed extensions to the original standard that are known as the Fidelity Range Extensions (FRExt). These extensions enable higher quality video coding by supporting increased sample bit depth precision 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, such as adaptive switching between 4×4 and 8×8 integer transforms, encoder-specified perceptual-based quantization weighting matrices, efficient inter-picture lossless coding, and support of additional color spaces. The design work on the Fidelity Range Extensions was completed in July 2004, and the drafting work on them was completed in September 2004.

Further recent extensions of the standard have included adding five new profiles intended primarily for professional applications, 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 that industry feedback indicated should have been designed differently.

Scalable Video Coding as specified in Annex G of H.264/AVC allows the construction of bitstreams that contain sub-bitstreams that conform to H.264/AVC. For temporal bitstream scalability, i.e., the presence of a sub-bitstream with a smaller temporal sampling rate than the 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. For spatial and quality bitstream scalability, i.e. the presence of a sub-bitstream with lower spatial resolution or quality than the bitstream, NAL (Network Abstraction Layer) removed from the bitstream when deriving the sub-bitstream. In this case, inter-layer prediction, i.e., the prediction of the higher spatial resolution or quality signal by data of the lower spatial resolution or quality signal, is typically used for efficient coding. The Scalable Video Coding extension was completed in November 2007.

The H.264 name follows the ITU-T naming convention, where the standard is a member of the H.26x line of VCEG video coding standards; 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. The name H.26L, referring to its ITU-T history, is less common, but still used. 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 codec 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.[1])

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Standardization committee and 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], USA). 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. Formal approval of the specification came in March 2003. The JVT was (is) chaired by Gary Sullivan, Thomas Wiegand, and Ajay Luthra (Motorola, USA). In June 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-Reiner Ohm (Aachen University, Germany). Since July 2006, the JVT works on Multiview Video Coding (MVC), an extension of H.264/AVC towards free viewpoint television and 3D television.

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Applications

Further information: List of video services using H.264/MPEG-4 AVC

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% [2] or more are reported. Digital Satellite TV quality, for example, was reported to be achievable at 1.5 Mbit/s, compared to the current operation point of MPEG 2 video at around 3.5 Mbit/s.[3] In order 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 3 mandatory video compression formats. Sony has also chosen this format for their Memory Stick Video format.[4]

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, although the standard is not yet used for fixed ATSC broadcasts within the United States.[5] [6] It has since been approved for use with the more recent ATSC-M/H (Mobile/Handheld) standard, using the AVC and SVC portions of H.264.[7]

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 compression only format, developed by Panasonic.

The CCTV (Close Circuit TV) or Video Surveillance market has included the technology in many products. Prior to this technology, the compression formats used within the industry's DVRs Digital Video Recorders were generally low quality in compression capability. With the application of the H.264 compression technology to the video surveillance industry, the quality of the video recordings became substantially improved. Starting in 2008, some in the surveillance industry promoted the H.264 technology as synonymous with "high quality" video.

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Patent licensing

In countries where patents on software algorithms are upheld, vendors and commercial users of products which make use of H.264/AVC are expected to pay patent licensing royalties for the patented technology[8] that their products use. This applies to the Baseline Profile as well.[9] A private organization known as MPEG LA, which is not affiliated in any way with the MPEG standardization organization, administers the licenses for patents applying to this standard, as well as the patent pools for MPEG-2 Part 1 Systems, MPEG-2 Part 2 Video, MPEG-4 Part 2 Video, and other technologies. The last US MPEG LA patents for H.264 may not expire until 2028[10].

On February 2, 2010 MPEG LA announced that H.264-encoded Internet Video that is free to end users would continue to be exempt from royalty fees until at least December 31, 2015. [11] However, other fees remain in place. The license terms are updated in 5-year blocks. [12]

In 2005, Qualcomm, which was the assignee of US Patents 5,452,104,[13] and 5,576,767[14] sued Broadcom in US District Court, alleging that Broadcom infringed the two patents by making products that were compliant with the H.264 video compression standard.[15] In 2007, the District Court found that the patents were unenforceable because Qualcomm had failed to disclose them to the JVT prior to the release of the H.264 standard in May 2003.[15] In December 2008, the US Court of Appeals for the Federal Circuit affirmed the District Court's order that the patents be unenforceable but remanded to the District Court with instructions to limit the scope of unenforceability to H.264 compliant products.[15]

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Patents and GNU Free Software licenses

Discussions are often held regarding the legality of free software implementations of formats like H.264, especially concerning the legal use of GNU LGPL and GPL implementations of H.264 and other patented formats. Consensus in discussions is that the allowable use depends on the laws of local jurisdictions. If operating or shipping a product in a country or group of countries where none of the patents covering H.264 apply, then using, for example, an LGPL implementation of the format is not a problem: There is no conflict between the software license and the (non-existent) patent license.

Conversely, shipping a product in the U.S. which includes (though not necessarily implements) a GPL H.264 decoder/encoder requires that the copyright terms of the GPL license be upheld, otherwise conveying the codec would be in violation of the software license of the implementation. In simple terms, LGPL and GPL licenses version 3.0 and above require that any rights held in conjunction with distributing the code also apply to anyone receiving the code,[16] and no further restrictions are put on distribution or use.[17] A product which incorporates GPLed code must not rely upon a discriminatory patent license that would prohibit the user from exercising rights granted to them by the GPL.[18] Thus, the right to distribute patent-encumbered code under those licenses as part of the product is revoked per the terms of the GPL and LGPL.[18] It should be realized that the party who would enforce any such breach of copyright would be the people who hold copyright: its writers, whereby any suit on a breach of that clause would have to argue that there exist valid, applicable patents that apply to the capabilities GPL licenced code,[18] a stance copyright holders[nb 1] have not taken.[19]

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Features

H.264/AVC/MPEG-4 Part 10 contains a number of new features that allow it to compress video much more effectively than older standards and to provide more flexibility for application to a wide variety of network environments. In particular, some such key features include:

Multi-picture inter-picture prediction including the following features:

Using previously-encoded pictures as references in a much more flexible way than in past standards, allowing up to 16 reference frames (or 32 reference fields, in the case of interlaced encoding) to be used in some cases. This is in contrast to prior standards, where the limit was typically one; or, in the case of conventional "B pictures", two. This particular feature usually allows modest improvements in bit rate and quality in most scenes. But in certain types of scenes, such as those with repetitive motion or back-and-forth scene cuts or uncovered background areas, it allows a significant reduction in bit rate while maintaining clarity.

Variable block-size motion compensation (VBSMC) with block sizes as large as 16×16 and as small as 4×4, enabling precise segmentation of moving regions. The supported luma prediction block sizes include 16×16, 16×8, 8×16, 8×8, 8×4, 4×8, and 4×4, many of which can be used together in a single macroblock. Chroma prediction block sizes are correspondingly smaller according to the chroma subsampling in use.

The ability to use multiple motion vectors per macroblock (one or two per partition) with a maximum of 32 in the case of a B macroblock constructed of 16 4×4 partitions. The motion vectors for each 8×8 or larger partition region can point to different reference pictures.

The ability to use any macroblock type in B-frames, including I-macroblocks, resulting in much more efficient encoding when using B-frames. This feature was notably left out from MPEG-4 ASP.

Six-tap filtering for derivation of half-pel luma sample predictions, for sharper subpixel motion-compensation. Quarter-pixel motion is derived by linear interpolation of the halfpel values, to save processing power.

Quarter-pixel precision for motion compensation, enabling precise description of the displacements of moving areas. For chroma the resolution is typically halved both vertically and horizontally (see 4:2:0) therefore the motion compensation of chroma uses one-eighth chroma pixel grid units.

Weighted prediction, allowing an encoder to specify the use of a scaling and offset when performing motion compensation, and providing a significant benefit in performance in special cases—such as fade-to-black, fade-in, and cross-fade transitions. This includes implicit weighted prediction for B-frames, and explicit weighted prediction for P-frames.

Spatial prediction from the edges of neighboring blocks for "intra"coding, rather than the "DC"-only prediction found in MPEG-2 Part 2 and the transform coefficient prediction found in H.263v2 and MPEG-4 Part 2. This includes luma prediction block sizes of 16×16, 8×8, and 4×4 (of which only one type can be used within each macroblock).

Lossless macroblock coding features including:

A lossless "PCM macroblock" representation mode in which video data samples are represented directly,[20] allowing perfect representation of specific regions and allowing a strict limit to be placed on the quantity of coded data for each macroblock.

An enhanced lossless macroblock representation mode allowing perfect representation of specific regions while ordinarily using substantially fewer bits than the PCM mode.

Flexible interlaced-scan video coding features, including:

Macroblock-adaptive frame-field (MBAFF) coding, using a macroblock pair structure for pictures coded as frames, allowing 16×16 macroblocks in field mode (compared with MPEG-2, where field mode processing in a picture that is coded as a frame results in the processing of 16×8 half-macroblocks).

Picture-adaptive frame-field coding (PAFF or PicAFF) allowing a freely-selected mixture of pictures coded as MBAFF frames with pictures coded as individual single fields (half frames) of interlaced video.[clarification needed]

New transform design features, including:

An exact-match integer 4×4 spatial block transform, allowing precise placement of residual signals with little of the "ringing" often found with prior codec designs. This is conceptually similar to the well-known DCT design, but simplified and made to provide exactly-specified decoding.

An exact-match integer 8×8 spatial block transform, allowing highly correlated regions to be compressed more efficiently than with the 4×4 transform. This is conceptually similar to the well-known DCT design, but simplified and made to provide exactly-specified decoding.

Adaptive encoder selection between the 4×4 and 8×8 transform block sizes for the integer transform operation.

A secondary Hadamard transform performed on "DC" coefficients of the primary spatial transform applied to chroma DC coefficients (and also luma in one special case) to obtain even more compression in smooth regions.

A quantization design including:

Logarithmic step size control for easier bit rate management by encoders and simplified inverse-quantization scaling.

Frequency-customized quantization scaling matrices selected by the encoder for perceptual-based quantization optimization.

An in-loop deblocking filter which helps prevent the blocking artifacts common to other DCT-based image compression techniques, resulting in better visual appearance and compression efficiency.

An entropy coding design including:

Context-adaptive binary arithmetic coding (CABAC), an algorithm to losslessly compress syntax elements in the video stream knowing the probabilities of syntax elements in a given context. CABAC compresses data more efficiently than CAVLC but requires considerably more processing to decode.

Context-adaptive variable-length coding (CAVLC), which is a lower-complexity alternative to CABAC for the coding of quantized transform coefficient values. Although lower complexity than CABAC, CAVLC is more elaborate and more efficient than the methods typically used to code coefficients in other prior designs.

A common simple and highly structured variable length coding (VLC) technique for many of the syntax elements not coded by CABAC or CAVLC, referred to as Exponential-Golomb coding (or Exp-Golomb).

Loss resilience features including:

A Network Abstraction Layer (NAL) definition allowing the same video syntax to be used in many network environments. One very fundamental design concept of H.264 is to generate self contained packets, to remove the header duplication as in MPEG-4's Header Extension Code (HEC).[21] This was achieved by decoupling information relevant to more than one slice from the media stream. The combination of the higher-level parameters is called a parameter set.[21] The H.264 specification includes two types of parameter sets: Sequence Parameter Set (SPS) and Picture Parameter Set (PPS). An active sequence parameter set remains unchanged throughout a coded video sequence, and an active picture parameter set remains unchanged within a coded picture. The sequence and picture parameter set structures contain information such as picture size, optional coding modes employed, and macroblock to slice group map.[21]

Flexible macroblock ordering (FMO), also known as slice groups, and arbitrary slice ordering (ASO), which are techniques for restructuring the ordering of the representation of the fundamental regions (macroblocks) in pictures. Typically considered an error/loss robustness feature, FMO and ASO can also be used for other purposes.

Data partitioning (DP), a feature providing the ability to separate more important and less important syntax elements into different packets of data, enabling the application of unequal error protection (UEP) and other types of improvement of error/loss robustness.

Redundant slices (RS), an error/loss robustness feature allowing an encoder to send an extra representation of a picture region (typically at lower fidelity) that can be used if the primary representation is corrupted or lost.

Frame numbering, a feature that allows the creation of "sub-sequences", enabling temporal scalability by optional inclusion of extra pictures between other pictures, and the detection and concealment of losses of entire pictures, which can occur due to network packet losses or channel errors.

Switching slices, called SP and SI slices, allowing an encoder to direct a decoder to jump into an ongoing video stream for such purposes as video streaming bit rate switching and "trick mode" operation. When a decoder jumps into the middle of a video stream using the SP/SI feature, it can get an exact match to the decoded pictures at that location in the video stream despite using different pictures, or no pictures at all, as references prior to the switch.

A simple automatic process for preventing the accidental emulation of start codes, which are special sequences of bits in the coded data that allow random access into the bitstream and recovery of byte alignment in systems that can lose byte synchronization.

Supplemental enhancement information (SEI) and video usability information (VUI), which are extra information that can be inserted into the bitstream to enhance the use of the video for a wide variety of purposes.[clarification needed]

Auxiliary pictures, which can be used for such purposes as alpha compositing.

Support of monochrome, 4:2:0, 4:2:2, and 4:4:4 chroma subsampling (depending on the selected profile).

Support of sample bit depth precision ranging from 8 to 14 bits per sample (depending on the selected profile).

The ability to encode individual color planes as distinct pictures with their own slice structures, macroblock modes, motion vectors, etc., allowing encoders to be designed with a simple parallelization structure (supported only in the three 4:4:4-capable profiles).

Picture order count, a feature that serves to keep the ordering of the pictures and the values of samples in the decoded pictures isolated from timing information, allowing timing information to be carried and controlled/changed separately by a system without affecting decoded picture content.

These techniques, along with several others, help H.264 to perform significantly better than any prior standard under a wide variety of circumstances in a wide variety of application environments. H.264 can often perform radically better than MPEG-2 video—typically obtaining the same quality at half of the bit rate or less, especially on high bit rate and high resolution situations.[22]

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