SIST EN ISO/IEC 11172-2:1997

SLOVENSKI STANDARD
SIST EN ISO/IEC 11172-2:1997
01-december-1997
Information technology - Coding of moving pictures and associated audio for
digital storage media at up to about 1,5 Mbit/s - Part 2: Video (ISO/IEC 11172-
2:1993)
Information technology - Coding of moving pictures and associated audio for digital
storage media at up to about 1,5 Mbit/s - Part 2: Video (ISO/IEC 11172-2:1993)
Informationstechnik - Codierung von bewegten Bildern und damit verbundenen
Tonsignalen für digitale Speichermedien bis zu 1,5 Mbit/s - Teil 2: Video (ISO/IEC 11172
-2:1993)
Technologies de l'information - Codage de l'image animée et du son associé pour les
supports de stockage numérique jusqu'a environ 1,5 Mbit/s - Partie 2: Vidéo (ISO/IEC
11172-2:1993)
Ta slovenski standard je istoveten z: EN ISO/IEC 11172-2:1995
ICS:
35.040 Nabori znakov in kodiranje Character sets and
informacij information coding
SIST EN ISO/IEC 11172-2:1997 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO/IEC 11172-2:1997

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SIST EN ISO/IEC 11172-2:1997

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SIST EN ISO/IEC 11172-2:1997

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SIST EN ISO/IEC 11172-2:1997
INTERNATIONAL ISO/IEC
STANDARD 11172-2
First edition
1993-08-o 1
Information technology - Coding of
moving pictures and associated audio for
digital storage media at up to about
I,5 Mbit/s -
Part 2:
Video
- Codage de /‘image animee et du son
Technologies de I’informa tion
associ6 pour /es supports de stockage num&ique jusqu’a environ
7,5 Mbit/s -
Partie 2: Vid6o
Reference number
&O/l EC 11172-2: 1993(E)

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SIST EN ISO/IEC 11172-2:1997
ISOAEC 11172-2: 1993 (E)
Contents
. . .
111
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
iv
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
Section 1: General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
1.2 Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
Section 2: Technical elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
2.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
2.2 Symbols and abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
2.3 Method of describing bitstream syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
2.4 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Annexes
39
A 8 by 8 Inverse discrete cosine transform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
40
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B Variable length code tables
49
C Video buffering verifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
51
D Guide to encoding video . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
108
E Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
109
holders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
F List of patent
0 ISO/IEC 1993
All rights reserved. No part of this publication may be reproduced or utilized in any form or by
any means, electronic or mechanical, including photocopying and microfilm, without
permission in writing from the publisher.
ISO/IEC Copyright Office l Case Postale 56 l CH 1211 Geneve 20 l Switzerland
Printed in Switzerland.
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SIST EN ISO/IEC 11172-2:1997
ISOAEC 11172-2: 1993 (E)
0 ISOAEC
Foreword
IS0 (the International Organization for Standardization) and IEC (the Inter-
national Electrotechnical Commission) form the specialized system for
worldwide standardization. National bodies that are members of IS0 or
IEC participate in the development of International Standards through
technical committees established by the respective organization to deal
with particular fields of technical activity. IS0 and IEC technical com-
mittees collaborate in fields of mutual interest. Other international organ-
izations, governmental and non-governmental, in liaison with IS0 and IEC,
also take part in the work.
In the field of information technology, IS0 and IEC have established a joint
technical committee, lSO/IEC JTC 1. Draft International Standards adopted
by the joint technical committee are circulated to national bodies for vot-
ing. Publication as an International Standard requires approval by at least
75 % of the national bodies casting a vote.
International Standard lSO/IEC 11172-2 was prepared by Joint Technical
.
Committee lSO/IEC JTC 1, information technology, Sub-Committee SC 29,
Coded representation of audio, picture, multimedia and hypermedia infor-
ma tion.
lSO/IEC 11172 consists of the following parts, under the general title In-
formation technology - Coding of moving pictures and associated audio
for digital storage media at up to about 1,5 Mbit/s:
- Part 1: Systems
- Part 2: Video
- Part 3: Audio
- Part 4: Compliance testing
Annexes A, B and C form an integral part of this part of
‘IEC 11172.
Annexes D, E and F are for information only.
. . .
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Introduction
Note -- Readers interested in an overview of the MPEG Video layer should read this Introduction and then
proceed to annex D, before returning to clauses 1 and 2.
0.1 Purpose
This part of ISO/I.EC 11172 was developed in response to the growing need for a common format for
representing compressed video on various digital storage media such as CDs, DATs, Winchester disks and
optical drives. This part of ISO/IEC 11172 specifies a coded representation that can be used for
compressing video sequences to bitrates around 1,5 Mbit/s. The use of this part of ISOAEC 11172 means
that motion video can be manipulated as a form of computer data and can be transmitted cvld received over
existing and future networks. The coded representation can be used with both 625line and 525.line
television and provides flexibility for use with workstation and persond computer displays.
This part of ISO/IEC 11172 w(as developed to operate principally from storage media offering a continuous
transfer rate of about 1,5 Mbit/s. Nevertheless it can be used more widely than this because the approach
taken is generic.
0.1.1 Coding parameters
The intention in developing this part of ISO/IEC 11172 has been to defme a source 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 of coded bitstreams and decoders are contained in the bitstream
itself, This allows for example, the algorithm to be used for pictures with a variety of sizes and aspect
ratios and on channels or devices operating at a wide range of bitrates.
Because of the large range of the characteristics of bitstreams that can be represented by this part of ISO/IEC
11172, a sub-set of these coding parameters known as the “Constrained Par(ameters” has been defined. The
aim in defining the constrained parameters is to offer guidance about a widely useful range of parameters.
Conforming to this set of constraints is not a requirement of this part of ISO/IEC 11172. A flag in the
bitstream indicates whether or not it is a Constrained Parameters bitstream.
Summary of the Constrained Parameters:
Horizontal picture size Less than or equal to 768 pels
r
Vertical picture size Less than or equal to 576 lines
1 Picture area 1 Less than or equal to 396 macroblocks
Pel rate Less than or equal to 396x25 macroblocks/s
A
r
Picture rate Less than or equal to 30 Hz
I
Motion vector range Less than -64 to +63,5 pels (using half-pel vectors)
backward f code and forward f code c= 4 (see table D.7)]
L
Input buffer size (in VBV model) Less than &equal to 327 680-&s
1 Bitrate i Less than or eaual to 1 856 000 bits/s (constant bitrate) I
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 lossless as the exact pel 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 m(zke random access to the coded bitstream. Obtaining good
picture quality at the bitrates of interest demands a very high compression ratio, which is not achievable
with intraframe coding alone. The need for random access, however, is best satisfied with pure intr~aframe
coding. This requires a careful balance between intra- and interframe coding and between recursive and non-
recursive temporal redundancy reduction.
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o ISOAEC ISOAEC 11172-2:1993(E)
A number of techniques are used to achieve a high compression ratio. The first, which is almost
independent from this part of ISO/IEC 11172, is to select an appropriate spatial resolution for the signal
The algorithm then uses block-based motion compensation to reduce the temporal redundancy. Motion
compensation is used for causal prediction of the current picture from a previous picture, for noncausal
prediction of the current picture from a future picture, or for interpolative prediction from past and future
pictures. Motion vectors are defined for each 1693 by 164ine region of the picture. The difference signal,
the prediction error, is further compressed using the discrete cosine transform (DCT) to remove spatial
correlation before it is quantized in an irreversible process that discards the less important information.
Finally, the motion vectors are combined with the DCT information, and coded using variable length codes.
0.2.1 Temporal processing
Because of the conflicting requirements of random access and highly efficient compression, three main
picture types are defined.
11~.~~oded pictures (I-Pictures) are coded without reference to other pictures.
They provide access points to the coded sequence where decoding can begin, but are coded with only a
moderate compression ratio. Predictive coded pictures (P-Pictures) are coded more efficiently using motion
compensated prediction from a past intra or predictive coded picture and are generally used as a reference for
further prediction.
Bidirectionally-predictive coded pictures (B-Pictures) provide the highest degree of
compression but require both past and future reference pictures for motion compensation.
Bidirectionally-
predictive coded pictures are never used as references for prediction.
The organ&ion of the three picture
types in a sequence is very flexible. The choice is left to the encoder and will depend on the requirements of
the application. Figure 1 illustrates the relationship between the three different picture types.
Bi-directional
1 Prediction
Prediction
Figure 1
-- Example of temporal picture structure
The fourth picture type defined in this pcvt of ISO/IEC 11172, the D-picture, is provided to allow a simple,
but limited quality, fast-forward playback mode.
0.2.2 Motion representation - macroblocks
The choice of 16 by 16 macroblocks for the motion-compensation unit is a result of the trade-off between
increasing the coding efficiency provided by using motion information and the overhead needed to store it.
Each macroblock can be one of a number of different types. For example, intra-coded, forward-predictive-
coded, backward-predictive coded, and bidirectionally-predictive-coded macroblocks bidirectionally-predictive coded pictures Depending on the type of the macroblock, motion vector
information and other side information are stored with the compressed prediction error signal in each
macroblock. The motion vectors are encoded differenti,?lly with respect to the hast coded motion vector,
using variable-length codes. The mcurimum length of the vectors that may be represented can be
programmed, on a picture-by-picture basis, so that the most demanding applications c compromising the performance of the system in more normal situations.
It is the responsibility of the encoder to calculate appropriate motion vectors.
This part of ISOIIEC 11172
does not specify how this should be done.
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ISOAEC 1117202:1993 (E)
0.2.3 Spatial redundancy reduction
Both original pictures and prediction error signals have high spatial redundancy. This part of ISODX
11172 uses a block-based DCT method with visually weighted quantization and run-length coding. Each 8
by 8 block of the original picture for intra-coded macroblocks or of the prediction error for predictive-coded
macroblocks is transformed into the DCT domain where it is scaled before being quantized. After
quantization many of the coefficients are zero in value (and so two-dimensional run-length and variable
length coding is used to encode the remaining coefficients efficiently.
0.3 Encoding
fies the syntax and semantics of
This This part part of of ISOAEC ISOAEC 11172 11172 does does not not specify specify an an encoding encoding process. process. It It spa specifies the syntax and semantics of
the bitstream and the signal processing in the decoder. As a result, many options are left open to encoders
the bitstream and the signal processing in the decoder. As a result, many options are left open to encoders
to trade-off cost and speed against picture quality and coding efficiency.
to trade-off cost and speed against picture quality and coding efficiency. T This is clause clause is is a a brief brief description description of of
the functions that need to be performed by an encoder. Figure 2 shows th main functional blocks.
the functions that need to be performed by an encoder. Figure 2 shows the main functional blocks.
r
Legulator
t
.
/ \ .
/
VL
DCT -+ Q
Motion
* . *
Estimator
/ II
.
Si>u&nput pictures
1
Picture
i ‘p
- store I
Predictor
Where
DCT is discrete cosine transform
DC1 is inverse discrete cosine transform
Q is quantization
Q-’ is dequantization
VLC is v Figure 2
-- Simplified video encoder block diagram
The input vi&o signal must be digitized and represented as a luminance cvld two colour difference signals
(Y, Cb, Cr). This may be followed by preprocessing and format conversion to select an appropriate
window, resolution and input format. This part of ISO/IEC 11172 requires that the colour difference
signals (Cb and Cr) are subsampled with respect to the luminance by 2:l in both vertical and horizontal
directions and are reformatted, if necessary, as a non-interlaced signal.
The encoder must choose which picture type to use for each picture.
Having defined the picture types, the
encoder estimates motion vectors for each 16 by 16 macroblock in the picture.
In P-Pictures one vector is
needed for each non-intra macroblock and in B-Pictures one or two vectors If B-Pictures are used, some reordering of the picture sequence is necessary before encoding.
Because B-
Pictures are coded using bidirectional motion compensated prediction, they can only be decoded after the
subsequent reference picture (an I or P-Picture) h vi

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SIST EN ISO/IEC 11172-2:1997
o ISOAEC ISOAEC 11172-2:1993(E)
encoder so that the pictures arrive at the in the order for decoding. The COITect. display order is
decoder
recovered by the decoder.
The basic unit of coding within a picture is the macroblock. Within each picture, macroblocks are encoded
in sequence, left to right, top to bottom. Each macroblock consists of six 8 by 8 blocks: four blocks of
luminance, one block of Cb chrominance, and one block of Cr chrominance. See figure 3. Note that the
picture area 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 information to match the sensitivity of
the human visual system.
1
0
14 El
2
3
I33
Y
Cb Cr
Figure 3 -- Macroblock structure
Firstly, for a given macroblock, 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, a motion compensated prediction of the contents of the
block based on p data in the current macroblock to form (an error signal Thirdly, this error signal is separated into 8 by 8
blocks (4 lumin~ance and 2 chromincvlce blocks in each macroblock) and a discrete cosine transform is
performed on each block. Each resulting 8 by 8 block of DCT coefficients is quantized and the two-
dimensional block is scanned in a zig-zag order to convert it into a one-dimensional string of quantized DCT
coefficients. Fourthly, the side-information for the macroblock (mode, motion vectors etc) and the
quantized coefficient data are encoded. For maximum efficiency, a number of variable length code tables are
defined for the different data elements. Run-length coding is used for the quantized coefficient data.
A consequence of using different picture types ‘and variable length coding is that the overall data rate is
variable. In applications that involve a fixed-rate channel, a FIFO buffer may be used to match the encoder
output to the chcumel. 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 controlling.the bitt-ate. This
part of ISO/IEC 11172 specifies an abstract model of the buffering system (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 a bitstream 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 subsequent encoding. The quantized coefficients are dequ‘antized and an inverse 8 by 8 DCT is performed on
each block. The prediction error signaI produced is then added back to the prediction signal and limited to
the required range to give a decoded reference picture.
0.4 Decoding
Decoding is the inverse of the encoding operation. It is considerably simpler than encoding as there is no
need to perform motion estimation and there (are many fewer options. The decoding process is defined by
this part of ISO/IEC 11172. The description that follows is a very brief overview of one possible way of
decoding a bitstream. Other decoders with different c?rchitectures are possible. Figure 4 shows the main
functional blocks.
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ISOAEC 11172-2:1993 (E)
Quantizer stepsize
Picture
+ Buffer +
.
R&o&r b
7
+
Coded video
Reconstructed
bitstnam
output pictures
Motion Vectors
b Picture store
DCT-1 is inverse discrete cosine transform
is dequantization
Q-’
MUX-l is demultiplexing
VLD is variable length decoding
Figure 4 -- Basic video decoder block diagram
For fixed-rate applications, the channel fills a FIFO buffer at a constant rate with the coded bitstream. The
decoder reads this buffer and decodes the data elements in the bitstream according to the defined syntax.
As the decoder reads the bitstream, it identifies the start of a coded picture and then the type of the picture.
It decodes each macroblock in the picture in turn. The macroblock type and the motion vectors, if present,
are used to construct a prediction of the current macroblock based on p have been stored in the decoder. The coefficient data are decoded and dequantized. Each 8 by 8 block of
coefficient data is transformed by an inverse DCT (specified in annex A), and the result is added to the
prediction signal and limited to the defined range.
After all the macroblocks in the picture have been processed, the picture has been reconstructed, If it is an I-
picture or a P-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 to be re-ordered from the coded or&r to
their natural display order. After reordering, the pictures are available, in digital form, for post-processing
and display in any Incanner that the application chooses.
03 Structure of the coded video bitstream
This part of ISO/IEC 11172 specifies a syntax for a coded video bitstream. This syntax contains six layers,
each of which either supports a signal processing or a system function:
Function
Layers of the syntax
Random access unit: context
Sequence layer
Random access unit: video
Group of pictures layer
Primcvy coding unit
Picture layer
Resynchronization unit
Slice layer
Motion compensation unit
Macroblock layer
DCT unit
Block layer
016 Features supported by the algorithm
Applications using compressed video on digital storage media need to be able to perform a number of
operations in addition to normaI forward playback of the sequence. The coded bitstream has been designed
to support a number of these operations.
. . .
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o ISOAEC
0.6.1 Random access
Random access is an essential feature for video on a storage medium Random access requires that any
picture can be decoded in a limited amount of time. It implies the existence of access points in the
bitstream - that is segments of information that are identifiable and can be decoded without reference to other
segments of data. A spacing of two random access points (Intra-Pictures) per second 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 application-specific directory or other knowledge beyond the scope of this part of ISO/IEC
11172) to obtain a fast-forward and fast-reverse playback effect.
0.6.3 Reverse playback
Some applications may require the vi&o signal to be played in reverse order. This can be achieved in a
decoder by using memory to store entire groups of pictures after they have been decoded before being
displayed in reverse order. An encoder can make this feature easier by reducing the length of groups of
pictures.
0.6.4 Error robustness
Most digital storage media and communication channels are not error-free. Appropriate channel coding
schemes should be used and are beyond the scope of this part of ISO/IEC 11172. Nevertheless the
compression scheme defined in this part of ISO/IEC 11172 is robust to residual errors. The slice structure
allows a decoder to recover after a data error and to resynchronize its decoding. Therefore, bit errors in the
compressed data will cause errors 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
There is 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 at any picture. Nevertheless
a number of features have been included that enable editing of coded data.
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SIST EN ISO/IEC 11172-2:1997
ISO/IEC 11172-2:1993(E)
INTERNATIONAL STANDARD @ lSO’lEC
Information technology - Coding of moving
pictures and associated audio for digital storage
media at up to about I,5 Mbit/s -
Part 2:
Video
Section 1: General
1.1 Scope
This part of ISO/IEC 11172 specifies the coded representation of video for digitaI 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 11172 is compatible with standard 525. and 62%
line television formats, and it provides flexibility for use with personaI computer and workstation displays.
ISO/IEC 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 hczrd disks. Nevertheless it can
be used more widely than this because of the generic approach taken. The storage media may be directly
connected to the decoder, or via communications means such as busses, LANs, or telecommunications
links. This part of ISO/IEC 11172 is intended for non-interlaced video formats having approximately 288
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 ISO/IEC 11172. At the time of publication, the editions indicated were valid.
AI1 standards are subject to revision, and parties to agreements based on this part of ISO/IEC 11172 are
encouraged to investigate the possibility of applying the most recent editions of the standards indicated
below. Members of IEC and IS0 maintain registers of currently valid International Standards.
ISO/IEC 11172.1:1993 Information technology - Coding of moving pictures and associated audio for digital
storage media at up to about I,5 Mbitis - Part 1: Systems.
ISOAEC 11172.3:1993 Information technology - Coding of moving pictures and associated audio for digital
storage media at up to about 1,5 MbitLs - Part 3 Audio.
CCIR Recommendation 601-2 Encoding parameters of digital television for studios.
CCIR Report 624-4 Characteristics of systems for monochrome and colour television.
CCIR Recommendation 648 Recording of audio signals.
CCIR Report 955-2 Sound broadcasting by satellite for portable and mobile receivers, including Annex IV
Summary description of Advanced Digital System II.
CCITI’ Recommendation J.17 Pre-emphasis used on Sound-Programme Circuits.
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SIST EN ISO/IEC 11172-2:1997
0 ISOAEC
ISOAEC 11172-2:1993 (E)
IEEE Draft Standard P118OD2 1990 Specification for the implementation of 8x 8 inverse discrete cosine
trangonn’:
IEC publication 908:1987 CD Digital Audio System.

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SIST EN ISO/IEC 11172-2:1997
ISOAEC 11172-2: 1993 (E)
0 ISOAEC
Section 2: Technical elements
2.1 Definitions
For the purposes of ISOAEC 11172, the following definitions apply. If specific to a part, this is noted in
square brackets.
2.1.1 ac coefficient [video]: Any DCT coefficient for which the frequency in one or both dimensions
is non-zero.
2.1 .2 access unit [system]: In the case of compressed audio an access unit is an audio
access unit. In
picture.
the case of compressed video an access unit is the coded representation of a
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 coding noise to frequency bands i
...