ISO/IEC 13818-4:1998/Amd 1:1999
(Amendment)Information technology — Generic coding of moving pictures and associated audio information — Part 4: Conformance testing — Amendment 1: Advanced Audio Coding (AAC) conformance testing
Information technology — Generic coding of moving pictures and associated audio information — Part 4: Conformance testing — Amendment 1: Advanced Audio Coding (AAC) conformance testing
Technologies de l'information — Codage générique des images animées et des informations sonores associées — Partie 4: Essais de conformité — Amendement 1: Essai de conformité de codage audio avancé
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INTERNATIONAL ISO/IEC
STANDARD 13818-4
First edition
1998-12-01
AMENDMENT 1
1999-06-15
Corrected and reprinted
2000-04-01
Information technology — Generic coding
of moving pictures and associated audio
information —
Part 4:
Conformance testing
AMENDMENT 1: Advanced Audio Coding
(AAC) conformance testing
Technologies de l'information — Codage générique des images animées et
des informations sonores associées —
Partie 4: Essais de conformité
AMENDEMENT 1: Essai de conformité de codage audio avancé
Reference number
B C
ISO/IEC 13818-4:1998/Amd.1:1999(E)
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ISO/IEC 13818-4:1998/Amd.1:1999(E)
Foreword
ISO (the International Organization for Standardization) and IEC (the International
Electrotechnical Commission) form the specialized system for worldwide standardiz-
ation. National bodies that are members of ISO 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. ISO and IEC technical
committees collaborate in fields of mutual interest. Other international organizations,
governmental and non-governmental, in liaison with ISO and IEC, also take part in the
work.
In the field of information technology, ISO and IEC have established a joint technical
committee, ISO/IEC JTC 1. Draft International Standards adopted by the joint
technical committee are circulated to national bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the national bodies casting
a vote.
Amendment 1 to ISO/IEC 13818-4:1998 was prepared by Joint Technical
Committee ISO/IEC JTC 1, Information technology, Subcommittee SC 29, Coding of
audio, picture, multimedia and hypermedia information.
© ISO/IEC 1999
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or
utilized in any form or by any means, electronic or mechanical, including photocopying and micro-
film, without permission in writing from the publisher.
ISO/IEC Copyright Office • Case postale 56 • CH-1211 Genève 20 • Switzerland
Printed in Switzerland
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© ISO/IEC ISO/IEC 13818-4:1998/Amd.1:1999(E)
Information technology — Generic coding of moving pictures and
associated audio information — Part 4: Conformance testing
AMENDMENT 1
Advanced Audio Coding (AAC) conformance testing
1) Add the following reference to subclause 1.2 Normative References:
ITU-R Document TG10-2/3- E only, " Basic Audio Quality Requirements for Digital Audio Bit-Rate Reduction Systems for
Broadcast Emission and Primary Distribution", 28 October 1991.
2) Replace the following definitions in subclause 2.1 with the following:
2.1.142 low frequency enhancement (LFE) channel: A limited bandwidth channel for low frequency audio effects in a
multichannel system.
: A transform which has the property of time domain aliasing
2.1.151 modified discrete cosine transform (MDCT)
cancellation. An analytical expression for the MDCT can be found in B 2.3.1.2.
2.1.258 variable length code (VLC): A code word assigned by variable length encoder (see variable length coding).
: A procedure to obtain the symbols encoded with a variable length coding technique.
2.1.259 variable length decoder (VLD)
3) Add the following definitions in subclause 2.1 as indicated:
: All single_channel_elements (see 3.2.1) or channel_pair_elements (see 3.2.1) in one
2.1.145.1 main audio channels
program.
2.1.193.1 program [AAC]: A set of main audio channels, coupling_channel_elements (see 3.2.1), lfe_channel_elements (see
3.2.1), and associated data streams intended to be decoded and played back simultaneously. A program may be defined by
default (see 3.5.1) or specifically by a program_configuration_element (see 3.2.1). A given single_channel_element (see 3.2.1),
channel_pair_element (see 3.2.1), coupling_channel_element, lfe_channel_element or data channel may accompany one or
more programs in any given bitstream.
Defines the rate in Hertz which is used to digitize an audio signal during the sampling
2.1.214.1 Sampling Frequency (Fs):
process.
: Discrete frequency domain data output from the analysis filterbank.
2.1.230.1 spectral coefficients
2.1.259.1 variable length encoder: A procedure to assign variable length codewords to symbols.
4) Add the following Arithmetic Operator in subclause 2.2.1 following the operator
Sign(x) = -1 when x<0:
INT ( ) Truncation to integer operator. Returns the integer part of the real-valued argument.
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ISO/IEC 13818-4:1998/Amd.1:1999(E) © ISO/IEC
5) Add the following as subclause 2.6 for conformance testing of ISO/IEC 13818-7:1997, Information technology — Generic
coding of moving pictures and associated audio information — Part 7: Advanced Audio Coding (AAC):
2.6 Advanced Audio Coding (AAC)
2.6.1 Introduction
ISO/IEC 13818-7 describes the Advanced Audio Coding (AAC) system for multichannel audio. This part of ISO/IEC 13818
includes much flexibility to enable its use in many different applications. The flexibility is obtained by specifying a toolset that
contains several required and optional tools, as well as several parameterized elements in the bitstream.
This subclause of the specification specifies how tests can be designed to verify whether bitstreams and decoders meet the
requirements as specified in ISO/IEC 13818-7. These tests can be used for various purposes such as:
- manufacturers of encoders, and their customers, can use the tests to verify whether the encoder produces valid
bitstreams for a particular AAC profile.
- manufacturers of decoders and their customers can use the tests to verify whether the decoder meets the requirements
specified in ISO/IEC 13818-4 for the claimed decoder capabilities.
2.6.2 Scope
This subclause of this part of ISO/IEC 13818 specifies how tests can be designed to verify whether bitstreams and decoders
meet requirements specified in ISO/IEC 13818-7. In this part of ISO/IEC 13818, encoders are not addressed specifically. An
encoder may be said to be an ISO/IEC 13818-7 encoder if it generates bitstreams compliant with the syntactic and semantic
bitstream requirements specified in ISO/IEC 13818-7.
Characteristics of coded bitstreams and decoders are defined for ISO/IEC 13818-7. The characteristics of a bitstream define the
subset of the standard that is exploited in the bitstream. Examples are the applied values or range of the sampling rate and
bitrate parameters. Decoder characteristics define the properties and capabilities of the applied decoding process. An example
of a property is the applied arithmetic accuracy. The capabilities of a decoder specify which coded bitstreams the decoder can
decode and reconstruct, by defining the subset of the standard that may be exploited in decodable bitstreams. A bitstream can
be decoded by a decoder if the characteristics of the coded bitstream are within the subset of the standard specified by the
decoder capabilities.
Procedures are described for testing conformance of bitstreams and decoders to the requirements defined in ISO/IEC 13818-7.
Given the set of characteristics claimed, the requirements that must be met are fully determined by ISO/IEC 13818-7. This
subclause summarizes the requirements, cross references them to characteristics, and defines how conformance with them can
be tested. Guidelines are given on constructing tests to verify bitstream and decoder conformance. This part of ISO/IEC 13818
gives guidelines on how to construct bitstream test suites to check or verify decoder conformance. In addition, some test
bitstreams implemented according to those guidelines are provided as an electronic annex.
2.6.3 AAC Bitstream Characteristics
Bitstream characteristics specify the constraints that are applied by the encoder in generating the bitstream. These syntactic and
semantic constraints may, for example, restrict the range or the values of parameters that are encoded directly or indirectly in
the bitstream. The constraints applied to a given bitstream may or may not be known a priori .
Encoders may apply restrictions to the following parameters of the bitstream:
a) sampling frequency
b) mono_mixdown_element
c) stereo_mixdown_element
d) use of prediction in main profile
e) pulse_data
f) window_shape
g) program_config_element
h) M/S stereo
i) intensity stereo
j) TNS
k) data_stream_element
l) dependently switched coupling channel
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© ISO/IEC ISO/IEC 13818-4:1998/Amd.1:1999(E)
m) independently switched coupling channel
n) LFE channel
o) matrix-downmix
2.6.4 Decoder Characteristics
2.6.4.1 Profile Specification
The naming convention for ISO/IEC 13818-7 AAC decoders dictates that a decoder be specified as an A.L.I.D Channel
Profile ISO/IEC 13818-7 AAC Decoder, where A is replaced by the number of main audio channels, L by the
number of LFE channels, I by the number of independent coupling channels, D by the number of dependently switched
coupling channels, and Profile Name by the actual profile name (Main, Low-Complexity, or Scaleable Sampling Rate). An
example would be a 5.1.1.1 Channel Main Profile ISO/IEC 13818-7 AAC Decoder, indicating a decoder capable of decoding 5
main audio channels, one LFE channel, one independent coupling channel, and one dependent coupling channel, with each of
the channels using the profile specified. This can be abbreviated as M.5.1.1.1. Similarly, a Low Complexity decoder can be
specified by a leading "L", and an SSR profile by an "S".
A conforming decoder must support a minimum capability in terms of the number of main audio channels, LFE channels,
independent coupling channels, and dependent coupling channels as specified below:
Table 2-8 Minimum Decoder Capability for 1, 2, 3, 4, 5, and 7 Main Audio Channels vs. Profile
Number of Main Audio Channels Main Profile Low Complexity SSR Profile
Capability Profile Capability Capability
1 1.0.0.0 1.0.0.0 1.0.0.0
2 2.0.0.0 2.0.0.0 2.0.0.0
3 3.0.1.0 3.0.0.1 3.0.0.0
4 4.0.1.0 4.0.0.1 4.0.0.0
5 5.1.1.1 5.1.0.1 5.1.0.0
7 7.1.1.2 7.1.0.2 7.1.0.0
Note that a decoder may support more than the number of channel elements specified in the table above and still be a
conformant decoder. Thus, M.5.1.1.1, M.5.1.1.2, L.5.1.1.1,and S.5.1.0.0 are all conformant 5 channel configurations. However,
M.5.1.0.0, L.5.1.0.0, and S.5.0.0.0 are not conformant 5 channel configurations.
2.6.4.2 Decoder Modifications
A conforming decoder may also support any of the following modifications of some parameters in audio bitstreams:
Bitstream Characteristic Normative Clause Variation
sampling rate 3 a decoder may support only a subset of possible
sampling rates, decoder manufacturers must specify
the rates which are supported
profile 2.1 a decoder may support additional channel elements
beyond the minimums listed for its profile
program configuration 3.5 a decoder is only required to decode one program of a
multi-program bitstream
data_stream_element 3.6 a decoder is not required to store or present data
recovered from data_stream_elements
mono-mixdown element 3.3.8 a decoder is not required to present audio from the
mono-mixdown element
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ISO/IEC 13818-4:1998/Amd.1:1999(E) © ISO/IEC
stereo-mixdown element 3.3.8 a decoder is not required to present audio from the
stereo-mixdown element
matrix-mixdown 3.3.8 a decoder is not required to calculate a matrix-
mixdown signal
2.6.4.3 Decoder Buffer Requirements
Refer to 3.2.2 of ISO/IEC 13818-7.
2.6.5 Procedure to Test Bitstream Conformance
Each bitstream shall meet the syntactic and semantic requirements specified in ISO/IEC 13818-7. This subclause describes a set
of semantic tests to be performed on bitstreams. The procedure to verify whether the syntax is correct is straight forward and
therefore not defined in this subclause. In the description of the semantic tests it is assumed that the tested bitstream contains no
errors due to transmission or other causes. For each test the condition or conditions that must be satisfied are given, as well as
the prerequisites or conditions in which the test can be applied. Note that the application of these tests requires parsing of the
bitstream to the appropriate levels, which in some cases goes as far as the spectral_data recovery.
2.6.5.1 Parsing an ADIF header
shall be encoded with the value 0x41444946, the ASCII representation of the string „ADIF“.
adif_id:
2.6.5.2 Parsing ADTS headers
2.6.5.2.1 adts_fixed_header
syncword: shall be encoded with the binary value 1111 1111 1111.
shall not be encoded with the value 0.
ID:
layer: shall be encoded with the binary value 00.
shall not be encoded with the binary value 11.
profile:
sampling_frequency_index: shall be encoded with a value no greater than 0xb.
2.6.5.2.2 adts_variable_header
frame_length: shall be encoded with the length of the frame, including headers and error check (if present)
2.6.5.3 Decoding of raw data blocks
id_syn_ele: if a program configuration element (PCE) is present, it must be the first syntactic element in a raw_data_block,
indicated by id_syn_ele encoded with a value of ID_PCE
: ensure that element_instance_tag numbers within each element type are unique within each frame. This
element_instance_tag
restriction does not apply to data_stream_elements (DSE), which may have duplicated element_instance_tags.
2.6.5.4 Decoding an individual_channel_stream
ics_reserved_bit: must be set to zero
: must be <= num_swb_long or num_swb_short as appropriate for window_sequence and sampling frequency
max_sfb
2.6.5.5 Noiseless Coding
shall not be encoded with the binary values 1100 or 1101.
sect_cb[g][i]:
Intensity codebooks INTENSITY_HCB and INTENSITY_HCB2 shall not occur in a single_channel_element, the left channel
of a channel pair element, a coupling channel element, or an LFE. Intensity codebooks can only occur in a
channel_pair_element if the common_window field is set to 1.
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© ISO/IEC ISO/IEC 13818-4:1998/Amd.1:1999(E)
sect_len_incr: the sum of all sect_len_incr elements for a given window group shall equal max_sfb.
hcod_sf[ ]: shall on
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