INTERNATIONAL
`STANDARD
`
`ISDIIEC
`11172-2
`
`First edition
`1993-08-01
`
`Information technology — Coding of
`moving pictures and associated audio for
`digital storage media at up to about
`1,5 Mbitls —
`
`Part 2:
`
`Video
`
`Technologies de finformation «H Codage de I ‘image anirnée et du son
`associé pour les supports de stcckage numérique jusquflé environ
`1.5 Mbir/s —
`Partie 2: Vidéo
`
` Reference number
`
`ISO/IEC 11 172-2 1993(5)
`
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`ISO/IEC 11172-2: 1993 {E}
`
`Conlents
`
`Page
`
`Foieword .................................... . ., .......................................................... . .ii i
`
`Sectien 1: General ...................................................................................... .
`
`. 1
`
`1.}
`
`Scope ............................................................................................ ..1
`
`1.2
`
`Normative
`
`Section 2: Technical
`
`2.]
`
`2.2
`
`Symbols-and
`
`2.3 Method of describing bitslream syntax.................................................... I3
`
`2.r‘-
`
`Annexes
`
`A
`
`B
`
`C
`
`8 by S Inverse discrete cosine transionn
`
`Variable lengthcode
`
`Video buffering
`
`
`
`
`
`
`
`I5
`
`m ‘D
`
`D‘
`
`Guidetoenonding
`
`13
`
`F
`
`List of patent holders....................................................................... ..l09
`
`© ISO/IEC 1993
`All rights reserved. No part of this publication may be reproduced or utilized in any form 01 by
`any means, elactronic or mechanical, including phatocopying and microfilm, without
`permission in writing from the publisher.
`
`ISO/EEC Copyright Office - Case Postale 56 - CH 1211 Genéve 20 - Switzerland
`
`Printed in Switzerland.
`
`ii
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`o ISO/IEC
`
`ISO/lEC11172~2: 1993 (E)
`
`Foreword
`
`lSO itbe lnternationai O'ganization for Standardization) and IEC (the Inter-
`nationa Electrotechnical Commission) form the specialized system for
`worldwide standardization. Nafional bodies that are members of
`ISO or
`
`inzematicnal Standards through
`EEC participate i1 the development of
`technical committees established by the respective organization ‘to deal
`with particular fields oi
`techn-cal activity.
`ISO and IEC technical com-
`mittees collaborate in fields of mutual interest. Other international organ-
`izations, governmental and nongovernmental, in liaison with ISO and lEC,
`also take part in the work.
`1
`'
`
`In the field of inforrnazion technology, :80 and IEC have established a joint
`technical committee, ‘SO/IEC JTC 1. Daft International Standards adopted
`by the joint technical committee are circulated to national bodies for vet
`ing. Publication as an International Standard requires-app'o\raE by at least
`75% o‘ the national bodies casting a vote.
`'
`
`International Standard iSO/IEC 11172-2 was prepared by Joint Technicai
`_ Committee SSO/IEC JTC 1, information technology, Sugb-Committee SC 29,
`Coded representatioriof audio, picture, multimedia and hypermedia infcr~
`T mation.
`'
`'
`'
`i
`
`ISDIEC 11172 consists ol the following parts, under thegenera! title in-
`formation technology —' Coding of moving pictures and associated audio
`for digital storage media at up to about 1,5 Mbiflsz
`
`'— Part 1': Systems
`
`— Part 2.- "Video
`
`— Part 3: Audio
`
`—— Part 4: Compliance testing
`
`Annexes A, "B and C fo'rn'an integral part of this part of ISO/1 EC 11172.
`Annexes D, E and F are for information only.
`M
`-
`'
`
`
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`:30/rec 11172-2: 1993 (E)
`
`o ISO/IEC
`
`Introduction
`
`Note —- Readers interested in an overview of the MPEG Video layer should read this Introduction and then
`
`proceed to mnex D, before returning to clauses I and 2.
`
`0.1
`
`Purpose
`
`This part ofISOIIEC 11 172 was developed in response to the growing need for a common format for
`representing compressed video on various digital storage media such as CD3, DATs, Winchester disks and
`optical drives. This part of 1S0/IEC 11172 specifies a coded representation that can be used for
`compressing video sequences to bitrates around 1,5 Mhitls. The use of this part of ISO/EEC 11172 means
`thatmotion video can be manipulated as aform ofcomputer data and can be trarrsnrjtted and received over
`existing and future networks. The coded representation can be used with both 625 -line and 525—line
`television and provides flexibility for use with workstation and personal computer displays.
`
`'Ihis part ofISO/IEC 11172 was developed to operate principally from storage media offering acorrtinuous
`transfer rate of about 1.5 .Vlbitr’s. Neverthelessit can be used more widely than this because the approach
`taken is generic.
`
`0.1.1 Coding parameters
`
`'1be intention indevelopiog this part of ISOIIKI 1.1172 has been to define asource coding algorithm with a
`large degree of flexibility that can be used in many different applications. To achieve this goal, a number of
`the parameters defining the characteristics ofcoded bitstr-cams and decoders are contained inthe bitstream
`itself. This allows for example, the algorithm to be used for pictures witha variety of sizes and aspect
`ratios and on channels or devices operating at awide range of bitrates
`
`Betnuse of the large range of the characteristics of bitstreams that can be represented by this part of ISOIIEC
`11172. a sub-set of these coding parameters lcnowrr as the "Constrained Parameters" lrasbeen defined. The
`aim in defining the constrained parameters is to offer guidance about a widely useful range ofparameters.
`Conforming to this set of oonstzraints is not a. requirement of this part of ISOIIEC 11172. A flag in the
`bitstream indicates whether or not it is a Constrained Parameters lritstrerm.
`
`Summary of the Constrained Parameters:
`
`
`
`
`
` Vertical icture size
`
`Less thanore at to 576 lines
`
`Less than or ‘ t al to 396 macrobloclzs
`
`
`
`
`
`
`
`
`
`
`Motron vector range
`
`In . mutter size r'inVBV model
`
`Less than -64 to +63,5 pels (using half-pel vectors)
`
`ackward f codeandtorward f code<=4 scet"ahleD.7
`Less ttrzrnoneuttl to 327 680 bits
`
`
`Less than oreual to 1 856 000 bits/s (constant bitrate
`
`0.2 Overview of the algorithm
`
`The coded representation defined in this part of ISO/IEC 11172 achieves a high compression ratio while
`preserving good picture quality. The algorithm is not lossiess as the exact pcl values are not preserved
`during coding. The choice of the techniques is based on the need to balance a high picture quality and
`compression ratio with the requirement to make random access to the coded bitstreant. Obtaining good
`picture quality atthe bitrates of interest demantls a very high compression ratio, which is not achievable
`with intrafrarne coding alone. ‘The need for random access, however, is best satisfied with pure intraframe
`coding- The requires a carefulbalance between intra and intertrame coding and between recursive and non-
`recursive temporal redundancy reduction.
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`© ISO/IEC
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`ISO/{EC 11172-2: 1993 (E)
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`A number of lecimiquesare used to achieve a high compression ratio. The lirst, which is almost
`independent from this part ofISOIEEC 11172, is to select an appropriate spatial resolution for the signal.
`The algorithm then u$s block-based motion compensation to reduce the temporal redundancy. Motion
`compensation is used for cause] prediction of the current picture from a previous picture, for non-causal
`prediction of the current picture from a futurepicture, or for irrterpolative prediction from past aid future
`pictures. Motion vectors are defined for each 16—pel by 16—line region of the picture. The difference signal,
`the prediction error. is further compressed using the discrete cosine transforrrt (DCI‘) to remove spatial
`correlation before it is quantized in an irreversible process mat discards the less important inforrnatim.
`Finally, the motion vectors are CO[l1biIl6d with the DCT information, and coded using vnriabie length codes-
`
`0.2.1 Temporal processing
`
`Because of die oontlicting requirements of random access and highly efficient compression, three main
`picture types are defined. Intra-coded pictures (I-Pictures) are coded without reference to other pictures.
`They provide access points to the coded sequence where decoding canbegin, butare traded with only a
`moderate compression ratio. Predictive coded pictures (P+Pictures) are codedrnore efficiently using rnotion
`compensated prediction from 21 pastintraor predictivecoded picture and are generally used as a reference for
`furrlrerprediction. Bidirectionally—preditIive coded picttres (B-Pictures) provide the highest degree of
`compression but require both part and fume reference pictures for motion compensation. Bidirectionally-
`predictive coded pictures are never used as references for prediction The organisation of the three picture
`types in “a sequenceis very flexible. The choice is left to the encoder and will depend on the requirements of
`the application. Figure I illustrates the relationship between the three differentpicurre types.
`
`Bi-directional
`
`Prediction
`
`Prediction
`
`Figure 1 -- Example of temporal picture structure
`
`The fourth picture type dcfmed in this part of ISO/IEC 11172, the D—picture, is provided to allowna simple,
`but limited quality, fasbforward playback mode.
`
`0.2.2 Motion representation - macroblocks
`
`The choice of 16 by 16 rnacroblocks for the motion-compensation u11it is aresult of the trade-off between
`increasing the coding efficitncy provided by using motion iuforrnauon and the overhead needed to storeit.
`Each macroblock can he one of a number of different types. For example. intra—coded, forward-predictive-
`coded, backward-predictive coded, and bidimctiorrally-predictive-coded rnacrobloclts are penrdued in
`hidireclionally-predictive coded pictures. Depending on the type of the rnacroblock, motion vector
`information and other side information are stored with the compressed prediction error signal in each
`macrohlock. Themotion vectors are encoded differentially with respect to the lust coded motion vector,
`using variable-length codes. The maxhnurn length of the vectors that may berepreseutod can be
`programmed, on a picture—by-picture basis, so that the most dernantling applications can be met without
`cornpromising the pm:-rnance of the system in more normal situations.
`
`It is the responsibility of the encoder to calculate appropriate motion vectors. This part of ISO/IEC l1l72
`does not specify how this should be done.
`
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`I
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`©ISO/JEC
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`6.2.3 Spatial redundancy reduction
`
`Both original pictures and prediction error signals have high spatial redundancy. This part of [SO/IEC
`11172 usesa block-based DCI‘ method with visually weighted quantization and run—iength coding. Each 8
`by 8 block of the original picmre for int:ra—coded Ioacrobloclzs or of the prediction errorfor predictive—coded
`rnacrobloclrs is transformed into the DCT domain where it is scaled before being quantized. After
`quanfzation many of the coefficients are zero in value and so two-citmensiottal run-length and variable
`length coding is used to encode the remaining coefficients efficiently.
`
`0.3 Encoding
`
`This part of ISOIIEC 11172 does not Specify an encoding process. It specifies the syntax and semantics of
`the bitstrearn and the signal processing in the decoder. As at result, many options are left open to encoders
`to trade—off cost and speed against picture quality and coding efficiency. This clause is abrief description of
`the functions that need to he performed by an encoder. Figure 2sh0w.s thernairt functional blocks
`
`Motion
`
`Source input pictures
`
`stimator
`
`DCT is discrete cosine transform
`
`DCT1 is inverse discrete cosine transform
`Q is quantization
`Q'] is dequantization
`VLC is variable length coding
`
`Figure 2 -- Simplified video encoder block diagram
`
`The input video signal -in um be digitized and rcpresentedas a luminance and two colour difference signals
`(Y, Cb, Cr). This may be followed by preprocessing and format conversion to selectan appropriate
`window. resolution and input format. This part of [S0/IEC 11172 requires that the colour difference
`signals (C3) and Cr) are subsarnpled with respect to the luminance by 2:! in both vertical and horizontal
`directions and are reformatted if necessary, as a non-interlaced signal.
`
`The encoder must choo$ which picture type to use for each picture. Having defined the pictureutypes, the
`encoder estimates motion vectors for each 16 by 16 macroblock in the picture.
`In P-Pictures one vector is
`needed for each nou—intra macroblock and in B—Pict1rres one or two vectors aneneeded.
`
`if B-Pictures are used sonic reordering of the picture sequence is necessary before encoding. Because B-
`Pictures are coded using bidirectional motion cornmnsated prediction, they can only be decoded after the
`subsequent reference picture (an I or P-Picture) hasbeen decoded. Therefore the pictures are reordered by the
`
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`© ISO/IEG
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`ISOIIEC 11172-2: 1993 (E)
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`encoderscthat the pictures arrive at the decoder in the order fordecoding. The correct dhplay order is
`recovered by the decoder;
`
`The basic unit of coding within a picture is the macrobiotic. Within each picture, macrobloclcs are encoded
`in sequence, left to right, top to bottom. Each nracroblock consists ‘of six 8 by 8 blocks: four blocks of
`luminance, one block of Ch chrcminance, and one bioek of Cr chrorninance. See figure 3. Note that the
`picture are: covered by the four blocks of luminance is the same as the area covered by each of the
`chrominance blocks. This is due to subsampling of the chrominance infonnation to match the sensitivity of
`the human visual system.
`-
`
`Y
`
`Ch
`
`Cr
`
`Figure 3 ~-
`
`'MacroI:olock structure
`
`,
`Firstly, fora given mrtcroblock, the coding mode is chosen. It depends on the picture type, the
`effectiveness of motion compensated prediction in that local region, and the nature of the signal within the
`block. Secondly, depending on the coding mode, arnotiort compensated prediction of the contents of the
`block based on past ancUor future reference pictures is iorrned. This prediction is subtracted from the actual
`data in the current rnacroblock to form an error signal. Thirdly, this error signal is separated into S by 8
`blocks (4 luminance and2 chrominance blocks in each macmblocic) and a discrete cosine transform is
`performed on each block. Each resulting 8 by 8 block of DCT coefficients is quantized and the two-
`diineusional block is scanned in a zigeeag Order to conven itinto a one—dirnensional string of quantized DCT
`coefficients. Fourthly, the side—inforrnation for the macrcblock (mode, motion vectors etc} and the
`quantized coefficient data are encoded. For maximum efficimcy, a number or’ variable length code tables are
`defined forthe different data elements. Rurrlengrh coding is used for the quantized coeffrcientdzta
`
`A consequence of using different picture types and variable length coding is that the overall datarate is
`variable. In applications that involve a fixed—rrte channel. aFlF0 buffer may be used to match the encoder
`output to the channel. The status of this buffer may be monitored to control the number of bits generated
`by the encoder. Controlling the quantization process is the most direct way of controllingthe bitrate. This
`part of ISO/JEC 1 1172 specifies an abstractmodel of the buffering systen1(the Video Buffering Verifier} in
`order to constrain the maximum variability in the number of bits that are used for a given picture. This
`ensures that abitstreain can be decoded with a buffer of known size.
`
`At this stage, the coded representation of the picture has been generated. The final step in the encoder is to
`regenerate I—Pictures and P-Pictures by decoding the data so that they can be used as reference pictures for.
`subsequent encoding. Tire quantized coefficients are dequan tized and an inverse 8 by 8 DC? is performed on
`each block. The prediction error signal produced is then added back to the prediction signal and limited to
`the required range to give a decoded reference picture.
`
`0.4 Decoding
`
`it is considerably simpler than encoding as there is no
`Decoding is the inverse of the encoding operation.
`need to perform motion estimation and there are many fewer options. The decoding process is defined by
`this part of ISOJIEC 11172. The descripticn that follows is a very brief overview of one possible way of
`decoding abitstrearn. Other decoders With different architectures are possible. Figure 4 shows the main
`functional blocks.
`
`.
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`“ISO/IEC 11172-2: 1993 (E)
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`©__|SOt'EEC
`
`
`
`Re:onsu-uetcd
`output pictures
`
`DCT'1 is inverse discrete cosine Uansfonn
`Q-1
`_ isdequantization
`MUX“‘1 is demultiplexing
`VLD
`is variable length decoding
`
`Figure 4 -- Basic video decoder block diagram
`
`For fixed—rate applications, the channel fills a FIET) buffer at a constant rate with the coded bitsh-eam The
`decoder reads this buffer and decodes the data elements in thebitstream according to the defined syntax.
`
`As the decoder reads the bitstream, -it identifies the start of a coded pictnreand then the type of the picture.
`It decodes each macrohlock in the picture in turn. The macroblodc type and the motion vectors, if present,
`are used to construct a prediction of the currentmacrobiock based on past and future reference pictures that
`--have been stored in thedecoder.
`‘The coefiicient dataare decoded and dequantized. Each 8 by 8 block of
`coefficient data is tnuisforrned by an inverse DCT (specified in annex A), and the insult is added to the
`prediction signal and limited to the defined range.
`
`After all the rnacrohlocks in the picture have been processed the picture has been reconstructed. If it is an [-
`picture or aP-picture it is a reference picture for subsequent pictures and is stored, replacing the oldest stored
`reference picture. Before the pictures are displayed they may need [0 be te—ordered from the coded order to '
`their namrai display older. Afterreordering: the pictures are available, in digitai form, for post-pmcessing
`and display in any manner that the appiication chooses.
`
`0.5
`
`Structure of the coded video bitstream
`
`This part of ISOHEC 11172 specifies a syntax for acotled video bitstrearn. This syntax contains six layers,
`each of which either supports a signal processing or a system function:
`
`La ers of the
`
`ntax
`
`Block la - r
`
`Sequence layer
`Group ofpictures layer
`Picture layer
`Slice layer
`Macroblock layer
`
`Random access unit: context
`Random access unit: video
`Pt‘i.rnaI’y coding unit
`Resynchronization unit
`Motion compensation unit
`DCT unit
`
`0.6 Features supported by the atgorithm
`
`Applications nsing compressed video on digital storage media need to be able to perform anumber of
`operations in addition to nonnal forward playback of the sequence. The coded bitstieum has been designed
`to support a number of these operations.
`
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`_© ISO/IEC
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`ISO/IEC 11172-2: 1993 (E)
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`G . 6 .1 Random access
`
`Random access is an essential feature for video ona storage inedinm. Random access requires that any
`picture can be decoded in a linited amount of tune. It implies the existence of access points in the
`hitstream — that is segments of information that are identifiable and can bedecoded without reference to other
`segments of data A spacing of two random access points [IIIIT-l—PiCttlItS) per secmd can be achieved
`without significant loss of picture quality.
`
`0. 6. 2 Fast search
`
`Depending on the storage medium, it is possible to scan the access points in a coded bitstream (with the
`help of an appIication~specific tirectory or other knowledge beyond the scope of this part of ISO/[EC
`1] 172) to obtain a Iast—forwarrl and fast—reverse playback effect.
`
`0.6 . 3 Reverse playback
`
`Some applications may require the video signal tobe played in reverse order. This canbc. achieved in a
`decoder by using memory to store entire groups ofpictures alter. they have been decoded before being
`displayed in reverse order. An encoder can make this feature easier by redicing the length of groups of
`pictures.
`
`0.5.4 Error robustness
`
`Most digital storage niediaand cotnmunication channels are not error—free. Appropriate channel coding
`schemes should be usedand are beyond the scope of this part of ISOIIEC 11172. Nevertheless the
`compression scheme defined in this part of ISO/[EC-11172 is robust to residual errors. The slioe structure
`allows a decoder torecover after a data error and to rcsynchmnize its decoding. Therefore, bit errors in the
`compressed data will cause eirors in the decoded pictures to be limited in area. Decoders may be able to use
`concealment strategies to disguise these errors.
`
`0.6.5 Editing
`
`Thereis a conflict between the requirement for high coding efficiency and easy editing. The coding structure
`and syntax have not been designed with the primary aim of simplifying editing atany picture. Nevertheless
`a number of features -have been included that enable editing of coded data
`
`
`
`
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`INTERNATIONAL STANDARD © '50"EC ISO/EEC 11172-2: 1993 (E)
`
`Information technology —- Coding of moving
`pictures and associated audio for digital storage
`media at up to about 1,5 Mbit/s —
`
`Part 2:
`Video
`
`Section 1: General
`
`1.1
`
`Scope
`
`This part Of130iIEC 11172 specifies the ooded representation of video for digital storage media and
`specifies the decoding process. The representation supports normal speed forward playback, as well as
`special functions such as random access, fast forward playback, fast reverse playback, normal speed reverse
`playback, pause and still pictures. This part of ISO/IEC 11 172 is compatble with standard 525- and 625-
`line television formats, and it provides flexibility for use with personal computer and workstation displays.
`
`ISOIIBC 11172 is primarily applicable to digital storage media supporting a continuous transfer rate up to
`about 1,5 Mbit/s, such as Compact Disc, Digital Audio Tape, and magnetic hard disks. Nevertheless itcan
`be used more widely than Ibis because of the generic approach mken. The storage media maybe directly
`connected to the decoder, or via mtniications means such as busses,LANs, or Lelecommunicafions
`links. This partof1SOlIEC 11172 is intended for non-interlaced video formats having approximately 238
`lines of 352 pels and picture rates around 24 Hz to 30 Hz.
`
`1.2 Normative references
`
`The following International Standards contain provisions which, through reference in this text, constitute
`provisions of this part of ISOIIEC 11172. At the time of publication, the editionsindicated were valid.
`All standards are subject to revision, and parties to agreements based on this part of ISOIJEC 1 1172 are
`encouraged to investigate the p0SS1bifity of applying the most recent editions of die. standards indicated
`below. Members of IEC and ISO maintain registers of currently valid International Standards.
`
`ISOIIEC 11172-1:1993 Information tecknc-logy— Coding of moving pictures and associated audz'o_for digital
`storage media or up I0 about 1.5 Mbit/5 — Part 1: Systems
`
`. [S0/IEC 11172321993 Information Iec}mology- Coding ofmoving pictures and arsociared audio for digital
`storage media at up to about 1,5 Mbit/.s'- Port 3 Audio.
`
`CCIR Recommendation 601-2 Encoding parameters ofdig ital television for studios.
`
`CCIR Report 624-4 Characteristics cfsysiemsjorrrwnochrome and colour television.
`
`CCIR Recornmendation 648 Recording of audio signals.
`
`CCIR Report 955-2 Sound broadcasting by satelliteforportable and mobile receivers, including Annex IV
`Surrtrnaiy description ofAdvanced I)igitaI System 11.
`
`CCITT Recommendation L17 Pr:-emphasis used on S0urLd—Pr.9gramme Circuits.
`
`1
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`ISO/{EC 11172-2: 1993 (E)
`
`© SSO/IEC
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`]EEE_D1afI Standard P1180/D2 1990 Speaficalion for {he implementation of8.r 8 inverse discrete msine
`1rarL.s_'fm1n".
`
`IEIC publicatiun 9{}8:1987 CD Digital Audio System.
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`© ISOIIEC
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`ISO/IEC 11172-2: 1993 [E]
`
`Section 2: Technical elements
`
`2.1 Definitions
`
`For the purposes of ISOIIEC 11172, the following definitions. apply. If specific to a part_ this is noted in
`squarebraclzets.
`
`2.1.1 ac coefiicient lvide-o]: Any DCT coefficient for which the frequency in one or both dimensions
`is non-zero.
`
`In the case of compressed audio an access unit is an audio access unit.
`2.1.2 access unit [system]:
`the case of compressed video an acce$ unit is the coded representation of a picture.
`
`In
`
`2.1.3 adaptive segmentation [audio]: A subdivision of the digital representation of an audio signal
`in variable segments of time.
`
`2.1.4 adaptive bit allocation [audio]: The assignment of bits to subbands in a time and frequency
`varying fashion according to a psychoacoustic model.
`'
`
`2.1.5 adaptive noise allocation [audio]: The assignment of ooding noise to frequency bands in a
`time and frequency varying fashion aocording to a psychoacoustic model.
`
`2.1.6 alias [audio]: Mirrored signal component resulting from sub-Nyqnist sampling.
`
`2.1.7 analysis filter-lsank [audio]: Filterbank in the encoder that transforms a broadband PCM audio
`signal into a set of subszunpled subband samples.
`
`2.1.3 audio access unit [audio]: For—l.ayers I and 11 an audio access unit is defined as the smallest
`parrot the encoded bitstnaam which car be decoded by itself, where decoded means “fully reconsructed
`sound‘- For layer [11 an audio actess unit is part of the bitstream that is decodable with the um of
`previously acquiredmajn information.
`
`2.1.9 audio buffer [audio]: A buffer in the system target decoder for storage of compressed audio data.
`
`2.1.10 audio sequence [audio]: A non-interrupted series of audio frames in which the following
`parameters arenot drangcdz
`- ID
`- Iaycr
`— Sampling Frequency
`- T0rLayer I and II: Bittate index
`
`2.1.11 backward motion vector [video]: A motion vector that is used for rnotion compensation
`from a reference picture at a later time in display order.
`
`2.1.12 Bark [audio]: Unit of critical baud rate. The Bark scale is anon-linear mapping of the frequency
`scale over the audio range closely corresponding with the hequency selectivity of the human ear across the
`band.
`
`2.1.13 bidirecfionally predictive-coded picture; B-picture [video]: A picture that is coded
`using motion compensated prediction from a past and'or future reference picture.
`
`2.1.14 bitrate: The rate at which the compressed bitstrcam is delivered from the storage medium to the
`input of a decoder.
`
`2.1.15 block companding [audio]: Normalizing of the digital representation of an audio signal
`within a certain time period.
`'
`
`2.1.16 block [video]: All 8—row by 8—co1urnu orthogonal block of pels.
`
`2.1.17 bound [audio]: The lowest sulaband in which intensity stereo coding is mad.
`
`3
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`2.1.18 byte aligned: A bit in a coded bitsmam is byte-aligned if its position is amtriripie of 8-hits
`from the firstbit in the stream.
`
`2.1.19 byte: Sequence of 8—bits.
`
`2.1.20 channel: A digital medium that stores or transports an ISOIIEC 11l72strearn.
`
`2.1.22 channel [audio]: The left and right channels of a stereo signal
`
`2.1.22 chrorninance (component) [video]: A matrix, block or single pel representing one of the
`two colour difference signals related to the primary colours in the manner defined in CCIR Rec 601. The
`symbols u@ for the colour difference signals are Cr and Cb.
`
`2.1.23 coded audio bitstrearn [audio]: A coded representation of an audio signal as specified in
`[S0/IEC 11172-3.
`
`2.1.24 coded video bitstream [video]: A coded representation of a series of one or more pictures as
`specified in this part of ISOIIEC 11172.
`,
`
`2.1.25 coded order [video}: The order in which the pictures are stored and decoded. This order is not
`necessarily the same as the display order.
`
`2.1.26 coded representation: A data elementas represented in its encoded fonn.
`
`2.1.27 coding parameters [video]: The set of user-definable parameters that characterize a coded video
`bitstream. Bitstreams are characterised by coding parameters. Decoders are characterised by the bitstreams
`that they are capable of decoding.
`
`2.1.28 component [video]: A matrix, block or single pei. from one of the three matrices (luminance
`and two chromiuance) that make up a picture,
`
`2.1.29 compress-ion: Reduction in the number of hits used to representan item of data.
`
`2.1.30 constant bitrate coded video [video]: A compressed video bitstream with a constant
`averagebitrate.
`
`2.1.31 constant hitrate: Operation where the bitrate is constant :"rorn start to finish of the compressed
`bitstreain.
`
`2.1.32 constrained parameters [video]: The values of the set of coding parameters defined in
`2.4.3.2.
`
`2.1.33 constrained system parameter stream (CSPS) [system]: An ISO/[EC 1 1172
`multiplexed stream for which the constraints defined in 2.4.6 of ISOIIEC 11172-1 apply.
`
`2.1.34 CRC: Cyclic redundancy code.
`
`2.1.35 critical band rate [audio]: Psychoacoustic function of frequency. At a given audible
`frequency it is proportional to the number of critical bands below that frequency. _ The units of the critical
`baud rate scale areBarks.
`
`2.1.36 critical band [audio]: Psychoacoustic measure in the spectral domain which oorresponds to the
`frequency seiectivity of the human ear. This selectivity is expressed in Bark.
`
`2.1.37 data element: An item of data as represented before encoding and after decoding.
`
`2.1.38 dc-coefficient [videoI: The DCT coefficient for which the frequency is zero in both
`dimensions.
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`2.1.39 rlc-coded picture; D-picture [video}: A picture that is coded using only inforrrration from
`itself. Of the DCT coefficients in the coded represcnraliorr, only the dc-coefficients are present
`
`2.1.40 DCT coefficient: The amplitude of a specific cosine basis fllI1CtiOl1.
`
`2.1.41 decoded stream: The decoded reconstruction of a compressed bitstream.
`
`2.1.42 decoder input buffer {video}: The first-in first-out
`buffering verifier.
`
`(FIFO) buffer specified in the video
`
`2.1.43 decoder input rate {video}: The data rate specified in the video buffering verifier and encoded
`in the coded video bitstream.
`
`2.1.44 decoder: An embodirnern of a decoding process-.
`
`2.1.45 decoding (process): The process defined in ISO/EEC 11172 that reads an input coded bitstream
`ard produces decoded pictures or audio samples.
`
`2.1.46 decoding time-stamp; DTS [system]: A held that may be present in a packet header that
`indicates the tirnelhat an access unit is decoded in the system targetdecorler.
`'
`
`2.1.47 dc-emphasis iaudiol: Filtering applied to an audio signal after storage or transmission to undo
`a linear distortion due to emphasis.
`'
`.
`
`2.1.48 dequantizatinn [video]: The process of rescaling the quantized DC1" coefficients after their
`representation in the hitsrream has been decoded and before they are presented to the inverse DCT.
`
`2.1.49 digital storage media; DSM: A digitalstorage or transrnission device or system.
`
`
`
`2.1.50 discrete cosine transform; DCT [video]: Either the forward discrete cosine transform or the
`inverse discrete cosine transform. The DCT is an nrverdble, discrete orthogonal transfonnation. The
`inverse DCI' is defined in annex A.
`'
`
`2.1.51 display order [video]: The order in which the decoded pictures should be displayed. Normally
`this is the same order in which they were p*en:nted at the input of the encoder.
`
`2.1.52 dual channel mode [audio]: A mode, where two audio channels Willi independent programme
`contents (e-g. bilingual) are encoded within one birstream. The coding process is the same as for the stereo
`mode.
`
`2.1.53 editing: The process by which one or more compressed bitstrearns are manipulated to produce it
`new co1nprc$ed bitstrezun. .Conforrning edited bitstreatns must meet the requirements defined in this part of
`ISO/IEC 11172.
`
`2.1.54 elementary stream [system]: A generic term for one of the coded video, coded audio or other
`coded bitstrearns.
`
`2.1.55 emphasis [audio]: Filtering applied to an audio signal before storage or transmission to
`improve the signal-to-noise ratio at high frequencies.
`
`2.1.56 encoder: An embodiment of an encoding process.
`
`2.1.57 encoding (proces