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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 11 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 12 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 13 14 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 15 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 edit 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 xavc is a recording format designed by sony that uses level 5 2 of h 264 mpeg 4 avc which is the highest level supported by that video standard 16 17 xavc can support 4k resolution 4096 2160 and 3840 2160 at up to 60 frames per second fps 16 17 sony has announced that cameras that support xavc include two cinealta cameras the sony pmw f55 and sony pmw f5 18 the sony pmw f55 can record xavc with 4k resolution at 30 fps at 300 mbit s and 2k resolution at 30 fps at 100 mbit s 19 xavc can record 4k resolution at 60 fps with 4 2 2 chroma sampling at 600 mbit s 20 21 design edit features edit 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 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 when chroma subsampling is used 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 halfpixel 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 integer discrete cosine transform integer dct 5 22 23 a type of discrete cosine transform dct 22 where the transform is an integer approximation of the standard dct 24 it has selectable block sizes 25 and exact match integer computation to reduce complexity 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 it is similar to the standard dct used in previous standards but uses a smaller block size and simple integer processing unlike the cosine based formulas and tolerances expressed in earlier standards such as h 261 and mpeg 2 integer processing provides an exactly specified decoded result 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 based on the standard dct 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 lossless macroblock coding features including a lossless pcm macroblock representation mode in which video data samples are represented directly 26 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 for encoding or as individual single fields 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 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 fo...