H.264 or MPEG-4 PART 10, ADVANCED VIDEO CODING ( MPEG-4 AVC) is a block-oriented motion-compensation -based video compression standard . As of 2014 it is one of the most commonly used formats for the recording, compression, and distribution of video content. It supports resolutions up to 4096×2304, including 4K UHD .
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 (i.e., half or less the bit rate of
MPEG-2 , H.263
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 ,
H.264 was developed by the ITU-T Video Coding Experts Group (VCEG) together with the ISO/IEC JTC1 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 one of the video encoding
Blu-ray Discs ; all
Blu-ray Disc players must be able to
decode H.264. It is also widely used by streaming internet sources,
such as videos from
YouTube , and the iTunes Store , web
software such as the
Adobe Flash Player and
H.264 is protected by patents owned by various parties. A license covering most (but not all) patents essential to H.264 is administered by patent pool MPEG LA . Commercial use of patented H.264 technologies requires the payment of royalties to MPEG LA 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 Systems pays royalties to MPEG LA on behalf of the users of binaries for its open source H.264 encoder.
* 1 Naming
* 2 History
* 2.1 Versions
* 3 Applications
* 3.1 Derived formats
* 4 Design
* 4.1 Features
* 4.2 Profiles
* 4.2.1 Feature support in particular profiles
* 4.3 Levels * 4.4 Decoded picture buffering
* 5 Implementations
* 5.1 Software encoders * 5.2 Hardware
* 6 Licensing * 7 See also * 8 References * 9 Further reading * 10 External links
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;
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
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
In early 1998, the
Video Coding Experts Group (
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
VCEG was chaired by Gary Sullivan (
In December 2001,
VCEG and the
Moving Picture Experts Group (
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 sampling structures known as Y'CbCr 4:2:2 (=YUV 4:2:2 ) and Y'CbCr 4:4:4. Several other features were 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 then included adding five other 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.
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 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.
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.
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. * Version 2 (Edition 1.1): (May 7, 2004) Corrigendum containing various minor corrections. * Version 3 (Edition 2): (March 1, 2005) Major addition to H.264/AVC containing the first amendment providing Fidelity Range Extensions (FRExt) containing High, High 10, High 4:2:2, and High 4:4:4 profiles.
* Version 4 (Edition 2.1): (September 13, 2005) Corrigendum
containing various minor corrections and adding three aspect ratio
* Version 5 (Edition 2.2): (June 13, 2006) Amendment consisting of
removal of prior High 4:4:4 profile (processed as a corrigendum in
* 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).
* Version 7 (Edition 2.3): (April 6, 2007) Amendment containing the
addition of High 4:4:4 Predictive and four Intra-only profiles (High
10 Intra, High 4:2:2 Intra, High 4:4:4 Intra, and
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% 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
Mbit/s and H.264 at only 1.5 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
Blu-ray Disc format and the now-discontinued HD
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. It has also been
approved for use with the more recent
Many common DSLRs use H.264 video wrapped in QuickTime MOV containers as the native recording format.
XAVC is a recording format designed by
This article IS IN A LIST FORMAT THAT MAY BE BETTER PRESENTED USING PROSE . You can help by converting this article to prose, if appropriate . Editing help is available. (April 2016)
Block diagram of H.264
H.264/AVC/ MPEG-4 Part 10 contains a number of new features that allow it to compress video much more efficiently 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. In profiles that support non-IDR frames, most levels specify that sufficient buffering should be available to allow for at least 4 or 5 reference frames at maximum resolution. This is in contrast to prior standards, where the limit was typically one; or, in the case of conventional "B pictures " (B-frames), 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 ).
* A lossless "PCM macroblock" representation mode in which video data samples are represented directly, 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 either as complete frames where both fields are combined together for encoding or as individual single fields.
* 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 design is conceptually
similar to that of the well-known discrete cosine transform (DCT),
introduced in 1974 by
N. Ahmed , T.Natarajan and K.R.Rao, which is
Citation 1 in
Discrete cosine transform . However, it is 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 design is conceptually similar to that of the
well-known DCT, but simplified and made to provide exactly specified
* Adaptive encoder selection between the 4×4 and 8×8 transform
block sizes for the integer transform operation.
* A secondary
* 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 that 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.
data more efficiently than
* 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). 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. 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. * 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 that lets an encoder 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. SEI FPA (Frame Packing Arrangement) message that contains the 3D arrangement:
* 0: checkerboard: pixels are alternatively from L and R. * 1: column alternation: L and R are interlaced by column. * 2: row alternation: L and R are interlaced by row. * 3: side by side: L is on the left, R on the right. * 4: top bottom: L is on top, R on bottom. * 5: frame alternation: one view per frame.
* Auxiliary pictures, which can be used for such purposes as alpha compositing . * Support of monochrome (4:0:0), 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.
Like other ISO/IEC
The standard defines a sets of capabilities, which are referred to as profiles, targeting specific classes of applications. These are declared as a profile code (profile_idc) and a set of constraints applied in the encoder. This allows a decoder to recognize the requirements to decode that specific stream.
Profiles for non-scalable 2D video applications include the following: Constrained Baseline Profile (CBP, 66 with constraint set 1) Primarily for low-cost applications, this profile is most typically used in videoconferencing and mobile applications. It corresponds to the subset of features that are in common between the Baseline, Main, and High Profiles. Baseline Profile (BP, 66) Primarily for low-cost applications that require additional data loss robustness, this profile is used in some videoconferencing and mobile applications. This profile includes all features that are supported in the Constrained Baseline Profile, plus three additional features that can be used for loss robustness (or for other purposes such as low-delay multi-point video stream compositing). The importance of this profile has faded somewhat since the definition of the Constrained Baseline Profile in 2009. All Constrained Baseline Profile bitstreams are also considered to be Baseline Profile bitstreams, as these two profiles share the same profile identifier code value. Extended Profile (XP, 88) Intended as the streaming video profile, this profile has relatively high compression capability and some extra tricks for robustness to data losses and server stream switching. Main Profile (MP, 77) This profile is used for standard-definition digital TV broadcasts that use the MPEG-4 format as defined in the DVB standard. It is not, however, used for high-definition television broadcasts, as the importance of this profile faded when the High Profile was developed in 2004 for that application. High Profile (HiP, 100) The primary profile for broadcast and disc storage applications, particularly for high-definition television applications (for example, this is the profile adopted by the Blu-ray Disc storage format and the DVB HDTV broadcast service). Progressive High Profile (PHiP, 100 with constraint set 4) Similar to the High profile, but without support of field coding features. Constrained High Profile (100 with constraint set 4 and 5) Similar to the Progressive High profile, but without support of B (bi-predictive) slices. High 10 Profile (Hi10P, 110) Going beyond typical mainstream consumer product capabilities, this profile builds on top of the High Profile, adding support for up to 10 bits per sample of decoded picture precision. High 4:2:2 Profile (Hi422P, 122) Primarily targeting professional applications that use interlaced video, this profile builds on top of the High 10 Profile, adding support for the 4:2:2 chroma subsampling format while using up to 10 bits per sample of decoded picture precision. High 4:4:4 Predictive Profile (Hi444PP, 244) This profile builds on top of the High 4:2:2 Profile, supporting up to 4:4:4 chroma sampling, up to 14 bits per sample, and additionally supporting efficient lossless region coding and the coding of each picture as three separate color planes.
For camcorders, editing, and professional applications, the standard
contains four additional
Intra-frame -only profiles, which are defined
as simple subsets of other corresponding profiles. These are mostly
for professional (e.g., camera and editing system) applications: High
10 Intra Profile (110 with constraint set 3) The High 10 Profile
constrained to all-Intra use. High 4:2:2 Intra Profile (122 with
constraint set 3) The High 4:2:2 Profile constrained to all-Intra use.
High 4:4:4 Intra Profile (244 with constraint set 3) The High 4:4:4
Profile constrained to all-Intra use.
As a result of the Scalable Video Coding (SVC) extension, the standard contains five additional scalable profiles, which are defined as a combination of a H.264/AVC profile for the base layer (identified by the second word in the scalable profile name) and tools that achieve the scalable extension: Scalable Baseline Profile (83) Primarily targeting video conferencing, mobile, and surveillance applications, this profile builds on top of the Constrained Baseline profile to which the base layer (a subset of the bitstream) must conform. For the scalability tools, a subset of the available tools is enabled. Scalable Constrained Baseline Profile (83 with constraint set 5) A subset of the Scalable Baseline Profile intended primarily for real-time communication applications. Scalable High Profile (86) Primarily targeting broadcast and streaming applications, this profile builds on top of the H.264/AVC High Profile to which the base layer must conform. Scalable Constrained High Profile (86 with constraint set 5) A subset of the Scalable High Profile intended primarily for real-time communication applications. Scalable High Intra Profile (86 with constraint set 3) Primarily targeting production applications, this profile is the Scalable High Profile constrained to all-Intra use.
As a result of the Multiview Video Coding (MVC) extension, the standard contains two multiview profiles: Stereo High Profile (128) This profile targets two-view stereoscopic 3D video and combines the tools of the High profile with the inter-view prediction capabilities of the MVC extension. Multiview High Profile (118) This profile supports two or more views using both inter-picture (temporal) and MVC inter-view prediction, but does not support field pictures and macroblock-adaptive frame-field coding. Multiview Depth High Profile (138)
Feature Support In Particular Profiles
FEATURE CBP BP XP MP PROHIP HIP HI10P HI422P HI444PP
I AND P SLICES Yes Yes Yes Yes Yes Yes Yes Yes Yes
BIT DEPTH (PER SAMPLE) 8 8 8 8 8 8 8 to 10 8 to 10 8 to 14
CHROMA FORMATS 4:2:0
4:2:0/ 4:2:2 4:2:0/ 4:2:2/ 4:4:4
FLEXIBLE MACROBLOCK ORDERING (FMO) No Yes Yes No No No No No No
ARBITRARY SLICE ORDERING (ASO) No Yes Yes No No No No No No
REDUNDANT SLICES (RS) No Yes Yes No No No No No No
DATA PARTITIONING No No Yes No No No No No No
SI AND SP SLICES No No Yes No No No No No No
INTERLACED CODING (PICAFF, MBAFF) No No Yes Yes No Yes Yes Yes Yes
B SLICES No No Yes Yes Yes Yes Yes Yes Yes
MULTIPLE REFERENCE FRAMES Yes Yes Yes Yes Yes Yes Yes Yes Yes
IN-LOOP DEBLOCKING FILTER Yes Yes Yes Yes Yes Yes Yes Yes Yes
CABAC ENTROPY CODING No No No Yes Yes Yes Yes Yes Yes
4:0:0 (MONOCHROME ) No No No No Yes Yes Yes Yes Yes
8×8 VS. 4×4 TRANSFORM ADAPTIVITY No No No No Yes Yes Yes Yes Yes
QUANTIZATION SCALING MATRICES No No No No Yes Yes Yes Yes Yes
SEPARATE CB AND CR QP CONTROL No No No No Yes Yes Yes Yes Yes
SEPARATE COLOR PLANE CODING No No No No No No No No Yes
PREDICTIVE LOSSLESS CODING No No No No No No No No Yes
As the term is used in the standard, a "level" is a specified set of constraints that indicate a degree of required decoder performance for a profile. For example, a level of support within a profile specifies the maximum picture resolution, frame rate, and bit rate that a decoder may use. A decoder that conforms to a given level must be able to decode all bitstreams encoded for that level and all lower levels.
Levels with maximum property values Level MAX DECODING SPEED MAX FRAME SIZE MAX VIDEO BIT RATE FOR VIDEO CODING LAYER (VCL) KBIT/S (BASELINE, EXTENDED AND MAIN PROFILES) Examples for high resolution @ highest frame rate Toggle additional details
LUMA SAMPLES/S MACROBLOCKS/S LUMA SAMPLES MACROBLOCKS
1 380,160 1,485 25,344 99 64 128×96@30 176×144@15
1B 380,160 1,485 25,344 99 128 128×96@30 176×144@15
1.1 768,000 3,000 101,376 396 192 128x96@60 176×144@30 352×email@example.com
1.2 1,536,000 6,000 101,376 396 384 128x96@120 176×144@60 352×288@15
1.3 3,041,280 11,880 101,376 396 768 128x96@172 176×144@120 352×288@30
2 3,041,280 11,880 101,376 396 2,000 128x96@172 176x144@120 352×288@30
2.1 5,068,800 19,800 202,752 792 4,000 176x144@172 352×240@60 352×288@50 352×480@30 352×576@25
2.2 5,184,000 20,250 414,720 1,620 4,000 176×144@172 352×480@30 352×576@25 720×480@15 720×firstname.lastname@example.org
3 10,368,000 40,500 414,720 1,620 10,000 176×144@172 352×240@120 352×480@60 720×480@30 720×576@25
3.1 27,648,000 108,000 921,600 3,600 14,000 352x288@172 352x576@130 640x480@90 720×576@60 1,280×720@30
3.2 55,296,000 216,000 1,310,720 5,120 20,000 640x480@172 720x480@160 720x576@130 1,280×720@60
4 62,914,560 245,760 2,097,152 8,192 20,000 720x480@172 720x576@150 1,280×720@60 2,048×1,024@30
4.1 62,914,560 245,760 2,097,152 8,192 50,000 720x480@172 720x576@150 1,280×720@60 2,048×1,024@30
4.2 133,693,440 522,240 2,228,224 8,704 50,000 720x576@172 1,280×720@140 2,048×1,080@60
5 150,994,944 589,824 5,652,480 22,080 135,000 1,024×768@172 1,280×720@160 2,048×1,080@60 2,560×1,920@30 3,680×1,536@25
5.1 251,658,240 983,040 9,437,184 36,864 240,000 1,280×720@172 1,920×1,080@120 2,048×1,536@80 4,096×2,048@30
5.2 530,841,600 2,073,600 9,437,184 36,864 240,000 1,920×1,080@172 2,048×1,536@160 4,096×2,160@60
6 1,069,547,520 4,177,920 35,651,584 139,264 240,000 2,048×1,536@300 4,096×2,160@120 8,192×4,320@30
6.1 2,139,095,040 8,355,840 35,651,584 139,264 480,000 2,048×1,536@300 4,096×2,160@240 8,192×4,320@60
6.2 4,278,190,080 16,711,680 36,651,584 139,264 800,000 4,096*2,304@300 8,192×4,320@120
The maximum bit rate for High Profile is 1.25 times that of the Base/Extended/Main Profiles, 3 times for Hi10P, and 4 times for Hi422P/Hi444PP.
The number of luma samples is 16x16=256 times the number of macroblocks (and the number of luma samples per second is 256 times the number of macroblocks per second).
DECODED PICTURE BUFFERING
Previously encoded pictures are used by H.264/AVC encoders to provide predictions of the values of samples in other pictures. This allows the encoder to make efficient decisions on the best way to encode a given picture. At the decoder, such pictures are stored in a virtual decoded picture buffer (DPB). The maximum capacity of the DPB, in units of frames (or pairs of fields), as shown in parentheses in the right column of the table above, can be computed as follows: capacity = min(floor(MaxDpbMbs / (PicWidthInMbs * FrameHeightInMbs)), 16)
Where MaxDpbMbs is a constant value provided in the table below as a function of level number, and PicWidthInMbs and FrameHeightInMbs are the picture width and frame height for the coded video data, expressed in units of macroblocks (rounded up to integer values and accounting for cropping and macroblock pairing when applicable). This formula is specified in sections A.3.1.h and A.3.2.f of the 2009 edition of the standard.
LEVEL 1 1B 1.1 1.2 1.3 2 2.1 2.2 3 3.1 3.2 4 4.1 4.2 5 5.1 5.2 6 6.1 6.2
MAXDPBMBS 396 396 900 2,376 2,376 2,376 4,752 8,100 8,100 18,000 20,480 32,768 32,768 34,816 110,400 184,320 184,320 696,320 696,320 696,320
For example, for an HDTV picture that is 1920 samples wide (PicWidthInMbs = 120) and 1080 samples high (FrameHeightInMbs = 68), a Level 4 decoder has a maximum DPB storage capacity of Floor(32768/(120*68)) = 4 frames (or 8 fields) when encoded with minimal cropping parameter values. Thus, the value 4 is shown in parentheses in the table above in the right column of the row for Level 4 with the frame size 1920×1080.
It is important to note that the current picture being decoded is not included in the computation of DPB fullness (unless the encoder has indicated for it to be stored for use as a reference for decoding other pictures or for delayed output timing). Thus, a decoder needs to actually have sufficient memory to handle (at least) one frame more than the maximum capacity of the DPB as calculated above.
In 2009, the HTML5 working group was split between supporters of Ogg
Theora , a free video format which is thought to be unencumbered by
patents, and H.264, which contains patented technology. As late as
July 2009, Google and Apple were said to support H.264, while Mozilla
and Opera support
Theora (now Google,
Mozilla and Opera all
On March 18, 2012, Mozilla announced support for H.264 in Firefox on mobile devices, due to prevalence of H.264-encoded video and the increased power-efficiency of using dedicated H.264 decoder hardware common on such devices. On February 20, 2013, Mozilla implemented support in Firefox for decoding H.264 on Windows 7 and above. This feature relies on Windows' built in decoding libraries. Firefox 35.0, released on January 13, 2015 supports H.264 on OS X 10.6 and higher.
On October 30, 2013,
Rowan Trollope from
Cisco published the source to OpenH264 on December 9, 2013.
AVC software implementations
B SLICES Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes
MULTIPLE REFERENCE FRAMES Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes
INTERLACED CODING (PICAFF, MBAFF) No MBAFF MBAFF MBAFF Yes Yes No Yes MBAFF Yes No
CABAC ENTROPY CODING Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes
8×8 VS. 4×4 TRANSFORM ADAPTIVITY No Yes Yes Yes Yes Yes Yes Yes No Yes Yes
QUANTIZATION SCALING MATRICES No No No Yes Yes No No No No No No
SEPARATE CB AND CR QP CONTROL No No No Yes Yes Yes No No No No No
EXTENDED CHROMA FORMATS No No No 4:2:2 4:4:4 4:2:0 4:2:2 4:2:2 4:2:2 No No 4:2:0 4:2:2 No
LARGEST SAMPLE DEPTH (BIT) 8 8 8 10 10 8 8 8 8 10 12
PREDICTIVE LOSSLESS CODING No No No Yes No No No No No No No
See also: List of cameras with onboard video stream encoding and H.264/ MPEG-4 AVC products and implementations
Because H.264 encoding and decoding requires significant computing power in specific types of arithmetic operations, software implementations that run on general-purpose CPUs are typically less power efficient. However, the latest quad-core general-purpose x86 CPUs have sufficient computation power to perform real-time SD and HD encoding. Compression efficiency depends on video algorithmic implementations, not on whether hardware or software implementation is used. Therefore, the difference between hardware and software based implementation is more on power-efficiency, flexibility and cost. To improve the power efficiency and reduce hardware form-factor, special-purpose hardware may be employed, either for the complete encoding or decoding process, or for acceleration assistance within a CPU-controlled environment.
CPU based solutions are known to be much more flexible, particularly when encoding must be done concurrently in multiple formats, multiple bit rates and resolutions (multi-screen video ), and possibly with additional features on container format support, advanced integrated advertising features, etc. CPU based software solution generally makes it much easier to load balance multiple concurrent encoding sessions within the same CPU.
The 2nd generation
A hardware H.264 encoder can be an ASIC or an FPGA .
ASIC encoders with H.264 encoder functionality are available from many different semiconductor companies, but the core design used in the ASIC is typically licensed from one of a few companies such as Chips -webkit-column-width: 30em; column-width: 30em; list-style-type: decimal;">
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* ITU-T publication page: H.264: Advanced video coding for generic audiovisual services *