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Text of the page (random words):
ac 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 27 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 27 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 27 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 for various purposes such as indicating the color space used the video content or various constraints that apply to the encoding sei messages can contain arbitrary user defined metadata payloads or other messages with syntax and semantics defined in the standard 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 sampling 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 video content 28 like other iso iec mpeg video standards h 264 avc has a reference software implementation that can be freely downloaded 29 its main purpose is to give examples of h 264 avc features rather than being a useful application per se some reference hardware design work has also been conducted in the moving picture experts group the above mentioned aspects include features in all profiles of h 264 a profile for a codec is a set of features of that codec identified to meet a certain set of specifications of intended applications this means that many of the features listed are not supported in some profiles various profiles of h 264 avc are discussed in next section profiles edit the standard defines several sets of capabilities which are referred to as profiles targeting specific classes of applications these are declared using a profile code profile_idc and sometimes a set of additional constraints applied in the encoder the profile code and indicated constraints allow a decoder to recognize the requirements for decoding that specific bitstream and in many system environments only one or two profiles are allowed to be used so decoders in those environments do not need to be concerned with recognizing the less commonly used profiles by far the most commonly used profile is the high profile 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 30 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 sampling 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 predictive profile constrained to all intra use cavlc 4 4 4 intra profile 44 the high 4 4 4 predictive profile constrained to all intra use and to cavlc entropy coding i e not supporting cabac 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 the multi resolution frame compatible mfc extension added two more profiles mfc high profile 134 a profile for stereoscopic coding with two layer resolution enhancement mfc depth high profile 135 the 3d avc extension added two more profiles multiview depth high profile 138 this profile supports joint coding of depth map and video texture information for improved compression of 3d video content enhanced multiview depth high profile 139 an enhanced profile for combined multiview coding with depth information feature support in particular profiles edit 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 0 4 2 0 4 2 0 4 2 0 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 cavlc entropy coding yes yes yes yes yes yes yes yes yes cabac entropy coding no no no yes yes yes yes yes yes 4 0 0 greyscale 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 c b and c r 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 levels edit 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 31 level maximum decoding speed macroblocks s maximum frame size macroblocks maximum video bit rate for video coding layer vcl constrained baseline baseline extended and main profiles kbits s examples for high resolution highest frame rate maximum stored frames toggle additional details 1 1 485 99 64 128 96 30 9 8 176 144 15 0 4 1b 1 485 99 128 128 96 30 9 8 176 144 15 0 4 1 1 3 000 396 192 176 144 30 3 9 320 240 10 0 3 352 288 7 5 2 1 2 6 000 396 384 320 240 20 0 7 352 288 15 2 6 1 3 11 880 396 768 320 240 36 0 7 352 288 30 0 6 2 11 880 396 2 000 320 240 36 0 7 352 288 30 0 6 2 1 19 800 792 4 000 352 480 30 0 7 352 576 25 0 6 2 2 20 250 1 620 4 000 352 480 30 7 12 352 576 25 6 10 720 480 15 0 6 720 576 12 5 5 3 40 500 1 620 10 000 352 480 61 4 12 352 576 51 1 10 720 480 30 0 6 720 576 25 0 5 3 1 108 000 3 600 14 000 720 480 80 0 13 720 576 66 7 11 1 280 720 30 0 5 3 2 216 000 5 120 20 000 1 280 720 60 0 5 1 280 1 024 42 2 4 4 245 760 8 192 20 000 1 280 720 68 3 9 1 920 1 080 30 1 4 2 048 1 024 30 0 4 4 1 245 760 8 192 50 000 1 280 720 68 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