Digital audio - Interface for non-linear PCM encoded audio bitstreams applying IEC 60958 - Part 11: MPEG-4 AAC and its extensions and MPEG-D USAC in LATM/LOAS

IEC 61937-11:2021 is available as IEC 61937-11:2021 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.IEC 61937-11:2021 describes the method to convey non-linear PCM bitstreams encoded in accordance with the MPEG-4 AAC format and its extensions (spectral band replication, parametric stereo and MPEG surround), and non-linear PCM bitstreams encoded in accordance with the MPEG-D USAC format, framed in MPEG-4 LATM/LOAS. IEC 61937-11:2021 cancels and replaces the first edition published in 2010, and Amendment 1:2018. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) MPEG-D USAC has been added.

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Published
Publication Date
14-Jul-2021
Current Stage
PPUB - Publication issued
Completion Date
15-Jul-2021
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IEC 61937-11
Edition 2.0 2021-07
INTERNATIONAL
STANDARD
Digital audio – Interface for non-linear PCM encoded audio bitstreams applying
IEC 60958 –
Part 11: MPEG-4 AAC and its extensions and MPEG-D USAC in LATM/LOAS
IEC 61937-11:2021-07(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 61937-11
Edition 2.0 2021-07
INTERNATIONAL
STANDARD
Digital audio – Interface for non-linear PCM encoded audio bitstreams applying
IEC 60958 –
Part 11: MPEG-4 AAC and its extensions and MPEG-D USAC in LATM/LOAS
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.160.30; 33.170 ISBN 978-2-8322-9950-0

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC 61937-11:2021 © IEC 2021
CONTENTS

FOREWORD ......................................................................................................................... 4

INTRODUCTION ................................................................................................................... 6

1 Scope ............................................................................................................................ 7

2 Normative references..................................................................................................... 7

3 Terms and definitions .................................................................................................... 7

3.1 Terms and definitions ............................................................................................ 7

3.2 Abbreviated terms ................................................................................................. 9

4 Mapping of the audio bit stream on to IEC 61937-1 ...................................................... 10

4.1 General ............................................................................................................... 10

4.2 Burst-info for MPEG-4 AAC and its extensions and MPEG-D USAC in

LATM/LOAS ........................................................................................................ 10

5 Format of data-burst for MPEG-4 AAC and its extensions and MPEG-D USAC in

LATM/LOAS ................................................................................................................ 10

5.1 General ............................................................................................................... 10

5.2 Pause data-bursts for MPEG-4 AAC and its extensions in LATM/LOAS ................ 11

5.3 Audio data-bursts ................................................................................................ 11

5.3.1 MPEG-4 AAC and its extensions in LATM/LOAS ........................................... 11

5.3.2 USAC in LATM/LOAS ................................................................................... 13

5.3.3 LATM/LOAS framing .................................................................................... 14

5.3.4 Latency ........................................................................................................ 15

Annex A (informative) Calculation of delay and data-burst repetition rates –

guidelines ........................................................................................................................... 16

A.1 Examples ............................................................................................................ 16

A.2 Guidelines........................................................................................................... 17

Annex B (normative) High-speed transmission ................................................................... 18

B.1 Indication ............................................................................................................ 18

B.2 Example.............................................................................................................. 18

Annex C (informative) MPEG-4 and MPEG-D audio profiles and audio object types ............ 19

C.1 Overview............................................................................................................. 19

C.2 MPEG-4 AAC Profile ........................................................................................... 19

C.3 MPEG-4 High-Efficiency AAC Profile ................................................................... 19

C.4 MPEG-4 High-Efficiency AAC v2 Profile ............................................................... 19

C.5 MPEG-D Baseline USAC Profile .......................................................................... 20

C.6 MPEG-D Extended HE-AAC Profile ...................................................................... 20

Bibliography ....................................................................................................................... 21

Figure 1 – Data-burst structure............................................................................................ 11

Figure 2 – Data-burst structure............................................................................................ 13

Figure 3 – Latency diagram for burst reception and decoding ............................................... 15

Figure C.1 – MPEG-4 /MPEG-D audio profiles structure ...................................................... 19

Table 1 – Values for data-type bits 0-4 and data-type bits 5-6 .............................................. 10

Table 2 – Repetition period of pause data-bursts ................................................................. 11

Table 3 – Data-type-dependent information for MPEG-4 AAC audio and its extensions

in LATM/LOAS .................................................................................................................... 12

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IEC 61937-11:2021 © IEC 2021 – 3 –

Table 4 – Data-type-dependent information for USAC audio in LATM/LOAS ......................... 14

Table A.1 – Examples – Calculation of delay and data-burst repetition rates for

AAC_LC and HE AAC ......................................................................................................... 16

Table A.2 – Examples – Calculation of delay and data-burst repetition rates for USAC ......... 17

Table B.1 – Indication fields ................................................................................................ 18

Table B.2 – Signalling example ........................................................................................... 18

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– 4 – IEC 61937-11:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DIGITAL AUDIO – INTERFACE FOR NON-LINEAR PCM
ENCODED AUDIO BITSTREAMS APPLYING IEC 60958 –
Part 11: MPEG-4 AAC and its extensions
and MPEG-D USAC in LATM/LOAS
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international

co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and

in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,

Publicly Available Specifications (PAS) and Guides (hereafter referred to as "IEC Publication(s)"). Their

preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with

may participate in this preparatory work. International, governmental and non-governmental organizations liaising

with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for

Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

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any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.

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6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

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expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent

rights. IEC shall not be held responsible for identifying any or all such patent rights.

IEC 61937-11 has been prepared by technical area 20: Analogue and digital audio, of IEC

technical committee 100: Audio, video and multimedia systems and equipment. It is an

International Standard.

This second edition cancels and replaces the first edition published in 2010, and

Amendment 1:2018. This edition constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:
a) MPEG-D USAC has been added.
---------------------- Page: 6 ----------------------
IEC 61937-11:2021 © IEC 2021 – 5 –
The text of this International Standard is based on the following documents:
Draft Report on voting
100/3523/CDV 100/3582/RVC

Full information on the voting for its approval can be found in the report on voting indicated in

the above table.
The language used for the development of this International Standard is English.

A list of all parts in the IEC 61937 series, published under the general title Digital audio –

Interface for non-linear PCM encoded audio bitstreams applying IEC 60958, can be found on

the IEC website.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in

accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available

at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are

described in greater detail at www.iec.ch/standardsdev/publications.

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under webstore.iec.ch in the data related to the

specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
---------------------- Page: 7 ----------------------
– 6 – IEC 61937-11:2021 © IEC 2021
INTRODUCTION

Modern digital video broadcasting standards, such as DVB, include support for the MPEG-4

HE AAC and/or HE AAC v2 audio codecs specified in ISO/IEC 14496-3. An increasing number

of countries are adopting these new codecs for their standard-definition and high-definition

digital video broadcasting services and have started with implementations.

For MPEG-2 AAC audio (ISO/IEC 13818-7), the specified framing format for the audio bit stream

is ADTS and its transport over an IEC 60958 interface is specified in IEC 61937-6.

However, the MPEG-4 (ISO/IEC 14496-3) and MPEG-D (ISO/IEC 23003-3) audio codecs

introduce new features and capabilities that require a framing format that supports more flexible

signalling and delivery mechanisms. Therefore, MPEG-2 systems (ISO/IEC 13818-1) specify

the MPEG-4 LATM/LOAS framing format for MPEG-4 audio codecs to overcome the limitations

of ADTS.

In order to be able to pass the MPEG-4 or MPEG-D audio bit stream from a set-top box to an

A/V receiver connected via the IEC 60958 interface without needing to reframe the audio bit

stream within ADTS, the MPEG-4 LATM/LOAS framing format needs to be supported by

IEC 61937, including the high-speed transmission protocol where the interface does not carry

an embedded sampling frequency clock.
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IEC 61937-11:2021 © IEC 2021 – 7 –
DIGITAL AUDIO – INTERFACE FOR NON-LINEAR PCM
ENCODED AUDIO BITSTREAMS APPLYING IEC 60958 –
Part 11: MPEG-4 AAC and its extensions
and MPEG-D USAC in LATM/LOAS
1 Scope

This part of IEC 61937 describes the method to convey non-linear PCM bitstreams encoded in

accordance with the MPEG-4 AAC format and its extensions (spectral band replication,

parametric stereo and MPEG surround), and non-linear PCM bitstreams encoded in accordance

with the MPEG-D USAC format, framed in MPEG-4 LATM/LOAS.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies.

For undated references, the latest edition of the referenced document (including any

amendments) applies.
IEC 60958-3:2021, Digital audio interface – Part 3: Consumer applications

IEC 61937-1:2021, Digital audio – Interface for non-linear PCM encoded audio bitstreams

applying IEC 60958 – Part 1: General

IEC 61937-2:2021, Digital audio – Interface for non-linear PCM encoded audio bitstreams

applying IEC 60958 – Part 2: Burst-info

ISO/IEC 14496-3:2019, Information technology – Coding of audio-visual objects – Part 3: Audio

ISO/IEC 23003-3:2020, Information technology – MPEG audio technologies – Part 3: Unified

speech and audio coding
3 Terms and definitions

For the purposes of this document, the terms, definitions and abbreviated terms of IEC 61937-1

and IEC 61937-2, and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1 Terms and definitions
3.1.1
access unit
smallest entity to which timing information can be attributed
Note 1 to entry: An access unit is the smallest individually decodable unit.
Note 2 to entry: A decoder consumes access units.
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– 8 – IEC 61937-11:2021 © IEC 2021
3.1.2
AudioMuxElement

LATM element that carries payload data for at least one audio elementary stream, related

payload length information, and multiplex configuration information

Note 1 to entry: This element carries payload data in form of PayloadMux elements. If the term is followed by a

number in parentheses, a "1" indicates that the multiplexing configuration (StreamMuxConfig) is multiplexed into the

AudioMuxElement, i.e. the multiplexing configuration (StreamMuxConfig) is transmitted "in-band". A "0" indicates

that the multiplexing configuration (StreamMuxConfig) is not present in the AudioMuxElement and needs to be

transmitted by other means ("out-of-band").
3.1.3
AudioSpecificConfig

configuration structure used to convey parameters to initialize the MPEG-4 audio decoder

3.1.4
LATM
low overhead MPEG-4 audio transport multiplex

multiplexing layer defined by ISO/IEC 14496-3 used for multiplexing of audio elementary

streams
3.1.5
LOAS
low overhead audio stream
synchronisation layer defined by ISO/IEC 14496-3

Note 1 to entry: Three different formats of LOAS are defined, each of which is designed to address the specific

characteristics of the underlying transmission layer.
3.1.6
MPEG-4 AAC profile
contains only the MPEG-4 AAC low complexity audio object type

Note 1 to entry: The MPEG-4 AAC low complexity object type is the counterpart to the MPEG-2 AAC low complexity

profile. In addition to the MPEG-2 AAC LC profile, the MPEG-4 AAC low complexity object type enables the usage

of the PNS tool.

Note 2 to entry: The MPEG-4 AAC low complexity object type is used when there are restrictions on the usage of

RAM and processing complexity.
3.1.7
MPEG-4 high-efficiency AAC profile

contains the spectral band replication object type in conjunction with the MPEG-4 AAC low

complexity object type

Note 1 to entry: For further information, see ISO/IEC 14496-3. The MPEG-4 high-efficiency AAC profile is a superset

of the MPEG-4 AAC profile.
3.1.8
MPEG-4 high-efficiency AAC profile version 2

contains the parametric stereo object type and the spectral band replication object type in

conjunction with the AAC low complexity object type

Note 1 to entry: The MPEG-4 high-efficiency AAC profile version 2 is a superset of the MPEG-4 high-efficiency AAC

profile.
3.1.9
MPEG-D Baseline USAC profile
profile that contains the Unified Speech and Audio Coding object type
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IEC 61937-11:2021 © IEC 2021 – 9 –
3.1.10
MPEG-D extended high-efficiency AAC profile

profile that contains the parametric stereo object type and the spectral band replication object

type in conjunction with the AAC low complexity object type, as well as the USAC object type

Note 1 to entry: The MPEG-D extended high-efficiency AAC profile is a superset of the MPEG-4 high-efficiency

AAC profile version 2 and the MPEG-D Baseline USAC profile.
3.1.11
MPEG surround

technology used for coding of multichannel signals based on a downmixed signal of the original

multichannel signal, and associated spatial parameters
Note 1 to entry: MPEG surround is defined in ISO/IEC 23003-1.
3.1.12
PayloadMux

payload data chunk in an AudioMuxElement that contains potentially multiplexed payload data

for multiple audio elementary streams

Note 1 to entry: In general, PayloadMux elements can be concatenated inside AudioMuxElements.

3.1.13
SpatialSpecificConfig
configuration structure used to initialize the MPEG surround decoder
3.1.14
StreamMuxConfig

configuration structure that describes the structure of the LATM payload multiplex

3.1.15
MDCT
modified discrete cosine transformation
transformation schema used by AAC
3.1.16
transformation length

number of audio samples or corresponding MDCT lines that are processed as a block per each

audio frame

Note 1 to entry: An MDCT line is a spectral component described by frequency, amplitude and phase.

3.1.17
USAC frame length
number of PCM audio samples per USAC frame

Note 1 to entry: USAC can operate in several modes using 1 024, 2 048, 4 096 or 768 linear PCM samples per

USAC frame.
3.2 Abbreviated terms
AAC Advanced Audio Coding
AAC LC MPEG-4 AAC Low Complexity
HE AAC MPEG-4 High-Efficiency AAC and MPEG-4 High-Efficiency AAC Version 2
ADTS Audio Data Transport Stream
DVB Digital Video Broadcasting
MDCT modified discrete cosine transformation
MPEG Moving Picture Experts Group
MPS MPEG Surround
---------------------- Page: 11 ----------------------
– 10 – IEC 61937-11:2021 © IEC 2021
PNS Perceptual Noise Substitution
PS parametric stereo
SBR spectral band replication
USAC Unified Speech and Audio Coding
LT AAC transformation length
4 Mapping of the audio bit stream on to IEC 61937-1
4.1 General

The coding of the bit stream and data-burst is in accordance with IEC 61937-1 and IEC 61937-2.

4.2 Burst-info for MPEG-4 AAC and its extensions and MPEG-D USAC in LATM/LOAS

The 16-bit burst-info contains information about the data found in the data-burst (see Table 1).

Table 1 – Values for data-type bits 0-4 and data-type bits 5-6
Data-type bits 0-
Data-type bits
4 according to
Repetition period
5-6
Reference
IEC 61937-2
Contents of data-bursts
point R
Value of Pc
in IEC 60958 frames
Value of
bits 5–6
Pc bits 0–4
0–22 0–3 According to IEC 61937
23 0 According to IEC 61937
1 AAC LC Bit 0 of Pa 960 / 1 024
2 HE AAC Bit 0 of Pa 1 920 / 2 048
3 According to IEC 61937
24 0–3 According to IEC 61937
25 0–2 According to IEC 61937
3 USAC Bit 0 of Pa 768 / 1 024 / 2 048 / 4 096
26-31 0–3 According to IEC 61937

Bits 0–4 of the burst-info (Pc) signal the data-type bits 0-4 used for transmission. For MPEG-4 AAC-based audio

in LATM/LOAS, the signalled data-type bits 0-4 is 23 (for AAC LC and HE AAC) or 25 (for USAC). Annex C gives

a brief overview of MPEG-4 AAC, its extensions, and MPEG-D USAC.

If the Pc bits 0-4 are equal to 23, the Pc bits 5–6 indicate if the transmitted data stream contains audio encoded

in AAC LC or HE AAC (including high-efficiency AAC version 2). Only values 1 and 2 refer to the transmission of

AAC LC or HE AAC based audio. The values 0 and 3 are used for indication of codec types which are described

by other or future parts of IEC 61937.

If the Pc bits 0-4 are equal to 25, the Pc bits 5–6 indicate if the transmitted data stream contains audio encoded

in USAC. Only value 3 refer to the transmission of USAC based audio. The values 0, 1 and 2 are used for indication

of codec types which are described by other or future parts of IEC 61937.
5 Format of data-burst for MPEG-4 AAC and its extensions and MPEG-D USAC
in LATM/LOAS
5.1 General

Clause 5 specifies the data-burst for MPEG-4 AAC audio and its extensions and MPEG-D USAC

in LATM/LOAS. Specific properties such as reference points, repetition period, the method of

filling stream gaps, and decoding latency are specified.
---------------------- Page: 12 ----------------------
IEC 61937-11:2021 © IEC 2021 – 11 –

The decoding latency (or delay), indicated for the data-type bits 5-6, should be taken into

account by the transmitter to schedule data-bursts as necessary to establish synchronisation

between picture and decoded audio.
5.2 Pause data-bursts for MPEG-4 AAC and its extensions in LATM/LOAS

Pause data-bursts for MPEG-4 AAC and its extensions in LATM/LOAS are defined in Table 2.

Table 2 – Repetition period of pause data-bursts
Repetition period of pause data-burst
Data-type of audio data-burst
Mandatory Recommended
Data-type bits 5-6 for MPEG-4 audio in
— 64 IEC 60958 frames
LATM/LOAS based on MPEG-4 AAC core codec

If regular audio data-bursts are not being transmitted due to for example a pause condition, it

is recommended to use pause data-bursts to fill such stream gaps. The repetition period of the

pause data-bursts should be selected in accordance with Table 2. If other repetition periods are

necessary to precisely fill the stream gap length, or to meet the requirement on audio data-

bursts spacing (see IEC 61937), pause data-bursts may have other lengths which can or not be

an integer multiple of 64 IEC 60958 frames.

When a stream gap in an audio stream is filled by a sequence of pause data-bursts, the Pa of

the first pause data-burst shall occur after exactly that amount of IEC 60958 frames as indicated

by the AAC transformation length in conjunction with the codec type information from Table 3.

It is recommended that the sequence(s) of pause data-bursts which fill the stream gap should

continue from this point up to the Pa of the first audio data-burst which follows the stream gap,

or as close as possible considering the specific IEC 60958 frame length of the pause data-burst

with respect to the AAC core codec transformation length. The repetition-period-length

parameter contained in the pause data-burst is intended to be interpreted by the receiver as an

indication of the number of decoded PCM samples that are missing (due to the resulting audio

gap).
5.3 Audio data-bursts
5.3.1 MPEG-4 AAC and its extensions in LATM/LOAS

The stream of data-bursts, as shown in Figure 1, consists of sequences of MPEG-4 AAC and

its extensions in LATM/LOAS frames. Each data-burst consists of a preamble followed by the

payload and stuffing. The data-type of a data-burst according to this specification is 23.

Figure 1 – Data-burst structure

The length of the audio payload data in the data-burst depends on the bit rate and other

parameters of the encoded audio. The size of the data-burst payload is indicated by the Pd

preamble word and is measured in bits.
P = 4 × 16 bit (P is the size of the preamble words Pa Pd measured in bits)
AD –
B = 4 × 16 bit (B is the size of the burst spacing measured in bits)
---------------------- Page: 13 ----------------------
– 12 – IEC 61937-11:2021 © IEC 2021
L = 1 024 or 960 lines (L is the used MDCT transformation length in MDCT lines)
T T

The maximum data-burst payload size for AAC not utilizing SBR is calculated according to the

following equation:
2 × 16 bit × L – ( P + B ) = maximum payload size in bits.
T AD S

If HE AAC is used, the maximum data-burst payload size is calculated according to the following

equation:
4 × 16 bit × L – ( P + B ) = maximum payload size in bits.
T AD S

The data-type-dependent information for MPEG-4 AAC and its extensions in LATM/LOAS is

given in Table 3. Bits 8–12 of Pc contain information about the audio codec used and about the

LATM configuration.
Table 3 – Data-type-dependent information for MPEG-4 AAC audio
and its extensions in LATM/LOAS
Bits of Pc
Value Definition Description
LSB…MSB
8 0 AAC Transformation 1 024 lines
Length
1 960 lines
9 0 PS PS data not present
1 PS data present
10–11 0 MPS MPS data not present
1 Embedded MPS data present / LATM single layer
transport mode (implicit MPS signalling)
2 Embedded MPS data present / explicit signalling
of MPS in second LATM layer
3 Do not use until further definition
12 0 Reserved Set to "0" until further definition
1 Do not use until further definition

The Pc bit 8 indicates the transformation length of the AAC core codec which is used to encode

the transmitted audio stream. Information from Pc bit 8 does not define the repetition period of

data-bursts on its own. This information is required in conjunction with the codec signalled by

the data-type bits 5-6 to calculate the data-burst repetition period. Receivers shall read the

data-type bits 5-6 as well as the data-type-dependent information in order to compute the

repetition period of data-bursts. Examples can be found in Annex A.
The Pc bit 9 indicates whether PS data is present in the encoded audio str
...

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