IEC 61937-11:2010

IEC 61937-11 ®
Edition 1.1 2018-11
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
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Digital audio – Interface for non-linear PCM encoded audio bitstreams applying
IEC 60958 –
Part 11: MPEG-4 AAC and its extensions in LATM/LOAS

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IEC 61937-11 ®
Edition 1.1 2018-11
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
colour
inside
Digital audio – Interface for non-linear PCM encoded audio bitstreams applying

IEC 60958 –
Part 11: MPEG-4 AAC and its extensions in LATM/LOAS

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.160.30; 33.170 ISBN 978-2-8322-6217-7

IEC 61937-11 ®
Edition 1.1 2018-11
CONSOLIDATED VERSION
REDLINE VERSION
colour
inside
Digital audio – Interface for non-linear PCM encoded audio bitstreams applying
IEC 60958 –
Part 11: MPEG-4 AAC and its extensions in LATM/LOAS

– 2 – IEC 61937-11:2010+AMD1:2018 CSV

 IEC 2018
CONTENTS
FOREWORD . 3

INTRODUCTION . 5

INTRODUCTION to Amendment 1 . 5

1 Scope . 6

2 Normative references . 6

3 Terms, definitions and abbreviations . 6

3.1 Terms and definitions . 6
3.2 Abbreviations . 8
4 Mapping of the audio bit stream on to IEC 61937-1 . 8
4.1 General . 8
4.2 Burst-info for MPEG-4 AAC and its extensions in LATM/LOAS . 8
5 Format of data-burst for MPEG-4 AAC and its extensions in LATM/LOAS . 9
5.1 General . 9
5.2 Pause data-bursts for MPEG-4 AAC and its extensions in LATM/LOAS . 9
5.3 Audio data-bursts . 10
5.3.1 MPEG-4 AAC and its extensions in LATM/LOAS . 10
5.3.2 LATM/LOAS framing . 12
5.3.3 Latency . 12
Annex A (informative) Calculation of delay and data-burst repetition rates – guidelines . 14
Annex B (normative) High-speed transmission . 16
Bibliography . 17

Figure 1 – Data-burst structure . 10
Figure 2 – Latency diagram for burst reception and decoding . 13

Table 1 – Values for data-type bits 0-4 and sub-data-type data-type bits 5-6 . 9
Table 2 – Repetition period of pause data-bursts . 9
Table 3 – Data-type-dependent information . 11
Table A.1 – Examples – Calculation of delay and data-burst repetition rates . 14
Table B.1 – Indication fields . 16

Table B.2 – Signalling example . 16

 IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
DIGITAL AUDIO –
INTERFACE FOR NON-LINEAR PCM ENCODED

AUDIO BITSTREAMS APPLYING IEC 60958 –

Part 11: MPEG-4 AAC and its extensions in LATM/LOAS

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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This consolidated version of the official IEC Standard and its amendment has been prepared
for user convenience.
IEC 61937-11 edition 1.1 contains the first edition (2010-05) [documents 100/1491/CDV and
100/1580/RVC] and its amendment 1 (2018-11) [documents 100/2948/CDV and 100/3033/RVC].
In this Redline version, a vertical line in the margin shows where the technical content is
modified by amendment 1. Additions are in green text, deletions are in strikethrough red text. A
separate Final version with all changes accepted is available in this publication.

– 4 – IEC 61937-11:2010+AMD1:2018 CSV

 IEC 2018
International Standard IEC 61937-11 has been prepared by technical area 4: Digital system
interfaces and protocols, of IEC technical committee 100: Audio, video and multimedia
systems and equipment.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts of IEC 61937, under the general title Digital audio – Interface for non-linear
PCM encoded audio bitstreams applying IEC 60958 can be found on the IEC website.

The committee has decided that the contents of the base publication and its amendment
will remain unchanged until the stability date indicated on the IEC web site
under "http://webstore.iec.ch" in the data related to the specific publication. At this
date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
 IEC 2018
INTRODUCTION
Modern digital video broadcasting standards such as DVB include support for the MPEG-4

HE AAC and/or HE AAC v2 audio codecs as 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) audio codecs introduce new features and

capabilities that require a framing format that supports more flexible signaling and delivery
mechanisms. Therefore, MPEG-2 Systems (ISO/IEC 13818-1) specifies 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 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.
INTRODUCTION to Amendment 1
The revision of IEC 61937-11:2010 has become necessary to specify the protocol where the
interface does not carry an embedded sampling frequency clock. The purpose is primarily to
support stereophonic multichannel audio applications increasing their channel counts. It is
justified in that ARIB introduces 22.2/7.1 audio channel applications, as given in ITU-R
BS.2051-0, into the market in 2018. This Amendment 1 contains the following significant
technical changes with respect to IEC 61937-11:2010:
• new Annex B specifies new high-speed transmission;
• the term "Sub-data-type" is discontinued.

– 6 – IEC 61937-11:2010+AMD1:2018 CSV

 IEC 2018
DIGITAL AUDIO –
INTERFACE FOR NON-LINEAR PCM ENCODED

AUDIO BITSTREAMS APPLYING IEC 60958 –

Part 11: MPEG-4 AAC and its extensions in LATM/LOAS

1 Scope
This part of IEC 61937 describes the method to convey non-linear PCM bitstreams encoded
according to the MPEG-4 AAC format and its extensions spectral band replication, parametric
stereo and MPEG surround, framed in MPEG-4 LATM/LOAS.
2 Normative references
The following referenced documents are indispensable for the application 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 (all parts), Digital audio interface
IEC 61937-1, Digital audio – Interface for non-linear PCM encoded audio bitstreams
applying IEC 60958 – Part 1: General
IEC 61937-2, Digital audio – Interface for non-linear PCM encoded audio bitstreams
applying IEC 60958 – Part 2: Burst-info
ISO/IEC 14496-3:2009, Information technology – Coding of audio-visual objects – Part 3:
Audio
3 Terms, definitions and abbreviations
For the purposes of this document the terms, definitions and abbreviations of IEC 61937-1,
IEC 61937-2 and the following apply.
3.1 Terms and definitions
3.1.1
access unit
smallest entity to which timing information can be attributed; an access unit is the smallest
individually decodable unit; a decoder consumes access units
3.1.2
AudioMuxElement(1)
LATM element that carries payload data for at least one audio elementary stream, related
payload length information and multiplex configuration information
NOTE This element carries payload data in form of PayloadMux elements. The number in brackets indicates
multiplexing configuration (StreamMuxConfig) is multiplexed into AudioMuxElements, that is in-band transmission.
3.1.3
AudioSpecificConfig
configuration structure used to convey parameters to initialize the MPEG-4 audio decoder

 IEC 2018
3.1.4
low overhead MPEG-4 audio transport multiplex

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

streams
3.1.5
low overhead audio stream
LOAS
synchronisation layer defined by ISO/IEC 14496-3; 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; 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 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 For further information please refer to 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 The MPEG-4 high efficiency AAC profile version 2 is a superset of the MPEG-4 high efficiency AAC profile.
3.1.9
MPEG surround
technology used for coding of multichannel signals based on a downmixed signal of the
original multichannel signal, and associated spatial parameters

NOTE MPEG surround is defined in ISO/IEC 23003-1.
3.1.10
PayloadMux
payload data chunk in an AudioMuxElement that contains potentially multiplexed payload data
for multiple audio elementary streams; in general PayloadMux elements can be concatenated
inside AudioMuxElements
3.1.11
SpatialSpecificConfig
configuration structure used to initialize the MPEG surround decoder
3.1.12
StreamMuxConfig
configuration structure that describes the structure of the LATM payload multiplex

– 8 – IEC 61937-11:2010+AMD1:2018 CSV

 IEC 2018
3.1.13
Sub-data-type
reference to the type of payload of the data-bursts defined for the use with the specified data-

type
3.1.14
modified discrete cosine transformation

MDCT
transformation schema used by AAC

3.1.15
transformation length (of the AAC codec or core codec)
AAC can operate in two modes using either a 960 lines or 1 024 lines MDCT transformation
for long blocks; an MDCT line is a spectral component described by frequency, amplitude and
phase
3.2 Abbreviations
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
PNS Perceptual Noise Substitution
PS Parametric Stereo
SBR Spectral Band Replication
TL 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 in LATM/LOAS
The 16-bit burst-info contains information about the data which will be found in the data-burst
(see Table 1).
 IEC 2018
Table 1 – Values for data-type bits 0-4 and sub-data-type data-type bits 5-6

Data-type bits 0- Sub-data-type

4 according to Data-type bits
Repetition period
Reference
IEC 61937-2 5-6
Contents of data-bursts
point R
in IEC 60958 frames
Value of Value of Pc
Pc bits 0–4 bits 5–6
0–22 0–3 According to IEC 61937

23 0 According to Definition specific to

IEC 61937-10 IEC 61937-10
1 AAC LC Bit 0 of Pa  960 / 1 024

2 HE AAC Bit 0 of Pa 1 920 / 2 048
3 Reserved for future reserved Reserved for future definition
definition of other of other applications
applications
24–31 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 signaled data-type bits 0-4 is 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.
5 Format of data-burst for MPEG-4 AAC and its extensions in LATM/LOAS
5.1 General
This clause specifies the data-burst for MPEG-4 AAC audio and its extensions in LATM/LOAS.
Specific properties such as reference points, repetition period, the method of filling stream
gaps and decoding latency are specified.
The decoding latency (or delay), indicated for the sub-data-types 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
Sub-data-type Data-type bits 5-6 for MPEG-4 audio
— 64 IEC 60958 frames
in 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 according to 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 may not be
an integer multiple of 64 IEC 60958 frames.

– 10 – IEC 61937-11:2010+AMD1:2018 CSV

 IEC 2018
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 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.

MPEG-4 LOAS framed MPEG-4 LOAS framed
Pa Pb Pc Pd Pa Pb Pc Pd
burst payload burst payload
Bit 0 of Pa Bit 0 of Pa
Stuffing
MPEG-4 LOAS frame MPEG-4 LOAS frame
Burst repetition period
IEC  1057/10
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 P – P measured in bits)
AD
AD A D
B = 4 × 16 bit  (B is the size of the burst spacing measured in bits)
S
S
TL = 1 024 or 960 lines (TL is the used MDCT transformation length in MDCT lines)
The maximum data-burst payload size for AAC not utilizing SBR is calculated according to the

following equation:
2 × 16 bit × TL – ( P + B ) = maximum payload size in bits.
AD S
If HE AAC is used the maximum data-burst payload size is calculated according to the
following equation:
4 × 16 bit × TL – ( P + B ) = maximum payload size in bits.
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.
 IEC 2018
Table 3 – Data-type-dependent information

Bits of Pc
Value Definition Description
LSB…MSB
8 0 AAC Transformation Length 1 024 lines

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 signaling)
2 Embedded MPS data present / explicit signaling 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
signaled by the sub-data-type data-type bits 5-6 to calculate the data-burst repetition period.
Receivers shall read the sub-data-types 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 stream.
The two Pc bits 10–11 indicate the presence and transport configuration of MPS data in the
encoded audio stream. The value 0 indicates that no MPS data is present. Values 1 and 2
indicate that MPS data is present in the audio bit stream. Pc bits 10-11 signaling 1 indicates
that the MPS payload as well as the MPS SpatialSpecificConfig is embedded inside the
payload of the first LATM layer which conveys the AAC LC or HE AAC data stream. Pc bits
10–11 signaling 2 indicates that the MPS payload is also embedded inside the payload of the
first layer. But in this case the MPS SpatialSpecificConfig is signaled explicitly associated to
the second layer inside the LATM StreamMuxConfig. The value 3 signaled by the Pc bits 10–
11 is reserved for future use.

This specification does not allow the transmission of MPS payload which is not embedded
inside the AAC LC or HE AAC payload but resides separated from the AAC LC or HE AAC
payload inside another LATM layer.
The presence of the PS or MPS extensions does not influence the data-burst repetition rate or
the calculation of the transmission and decoding latency as described in 5.3.3.
The Pc bit 12 is reserved for future use. This bit shall be set to 0.
One complete AAC access unit represents a time interval of 1 024 or 960 audio samples
embedded into the data-burst payload. When transmitting MPEG-4 HE AAC encoded audio
programs, SBR is used as an extension to AAC. In this case the sampling frequency of the
MPEG-4 AAC core component is usually half the sampling frequency of the SBR tool and
audio program. One complete HE AAC access unit represents a time interval of 2 048 or
1 920 audio samples embedded into the data-burst payload.

– 12 – IEC 61937-11:2010+AMD1:2018 CSV

 IEC 2018
HE AAC bit streams with downsampled SBR shall be transmitted signaling AAC LC in the sub-

data-type data-type bits 5-6. Therefore one access unit corresponds to 1 024 or 960 AAC

encoded audio samples.
If HE AAC is signaled by the sub-data-type data-type bits 5-6 the IEC 60958 frame rate shall

be equal to the sampling frequency of the SBR tool. If AAC LC is signaled the IEC 60958

frame rate shall correspond to the sampling frequency of AAC.

The reference point of a data-burst is bit 0 of Pa and occurs exactly once every number of

IEC 60958 sampling periods which is computed using the information from Table 1 and

Table 3. The data-burst containing one LATM/LOAS audio frame shall occur at a constant rate.

The intervals for data-bursts sharing the same bit-stream-number shall correspond exactly to
the amount of IEC 60958 frames which is calculated using the information from Table 1 and
Table 3.
It is not allowed to transmit audio data streams using IEC 60958 frame rates below 32 kHz.
5.3.2 LATM/LOAS framing
The LOAS frame as described in ISO/IEC 14496-3 shall be mapped directly to the payload
section, right after the preamble words of the data-burst. The first bit of the LOAS frame shall
always correspond to the first bit after the preamble section in the data-burst.
The payload in a data-burst consists of one complete LOAS frame containing one LATM
AudioMuxElement. It is not allowed to convey one LATM/LOAS frame using multiple data-
bursts. LOAS frames exceeding the payload capacity of a data-burst shall be dropped and the
actual data-burst shall be replaced by a sequence of pause-bursts to match the duration of
that data-burst.
The parameter numSubFrames from the LATM StreamMuxConfig shall be 0. The parameter
numProgram from the LATM StreamMuxConfig shall be 0. The parameter numLayer from the
LATM StreamMuxConfig shall be 0 except for audio streams signaling the availability of MPS
with payload embedding and explicit signaling of MPS in the second LATM layer. In such
cases the presence of a second layer in LATM frames is allowed and therefore numLayer
shall be 1 indicating 2 layers. In this configuration there exists no payload associated to the
second LATM layer and therefore the payload size indication for the second layer in LATM is
set to zero.
Only the LOAS AudioSyncStream() scheme shall be used in the context of this specification.
The LATM StreamMuxConfig structure shall be conveyed inside the LATM multiplex. This is
the main structure that is utilized by the decoder for configuration. The StreamMuxConfig may

not be present in each LATM frame in order to save bandwidth. It may be sent in intervals to
allow decoders to tune in to a running stream.
5.3.3 Latency
The latency of an external audio decoder to decode MPEG-4 AAC and its extensions in
LATM/LOAS is defined as the sum of the receiving time of the audio payload in one data-burst
and the time used for decoding of one access unit.
Each data-burst contains a minimum of 4 stuffing words (Pz of 16 bits). The repetition period
of data-bursts in IEC 60958 frames is computed according to information from Table 1 and
Table 3. The reception delay for one audio access unit is calculated as the time elapsed
counting from the first bit of the data-burst until the last bit of the actual audio payload inside
the data-burst received. Subsequent stuffing is not taken into account. After a complete frame
is received immediate decoding and subsequent rendering of the audio frame is not
recommended as the size of the next audio frame and therefore time required for receiving it
completely cannot be determined accurately.

 IEC 2018
In order to simplify the timing mechanism for receiving and decoding of content of data-bursts,

the receiving delay should be calculated as the time necessary to receive the complete data-

burst including the stuffing. The maximum time available to decode (the decoding delay)

should be selected to correspond to the length of one full data-burst. This results in an overall

delay corresponding to two complete data-bursts for reception and decoding.

For synchronisation (for example with video), the recommended value for latency corresponds

to the time necessary to receive two complete data-bursts. Figure 2 shows the simplified and

recommended method for calculating the latency for reception and decoding.

A shorter latency may be acceptable if synchronisation is not required.

LOAS framed LOAS framed
Pa Pb Pc Pd Pa Pb Pc Pd Pa
burst payload burst payload
Bit 0 of Pa Bit 0 of Pa
Stuffing
LOAS frame LOAS frame
Stuffing
Burst repetition period
Receiving delay Decoding delay
Latency of receiving and decoding
IEC  1058/10
NOTE This diagram shows the recommended method.
Figure 2 – Latency diagram for burst reception and decoding

– 14 – IEC 61937-11:2010+AMD1:2018 CSV

 IEC 2018
Annex A
(informative)
Calculation of delay and data-burst repetition rates – guidelines

A.1 Examples
Some examples for the calculation of data-burst-repetition rates and latencies can be found in

Table A.1.
Table A.1 – Examples – Calculation of delay and data-burst repetition rates
Data-burst
Bit 8 of Pc AAC sampling SBR sampling IEC 60958 Overall
Bits 5-6
repetition rate
TL rate rate frame rate latency
of Pc codec
IEC 60958
indication
lines kHz kHz kHz ms
frames
32 n/a 32 64
1 024 44,1 n/a 44,1 1 024 46,44
48 n/a 48 42,67
96 n/a 96 21,33
AAC LC
32 n/a 32 60
960 44,1 n/a 44,1 960 43,54
48 n/a 48 40
96 n/a 96 20
16 32 32 128
22,05 44,1 44,1 92,88
2 048
1 024
24 48 48 85,33
48 96 96 42,67
HE AAC
16 32 32 120
960 22,05 44,1 44,1 1 920 87,07
24 48 48 80
48 96 96 40
The presence of the PS or MPS extensions signaled by Pc bits 9–11 does not influence the
data-burst repetition rate or the calculation of the transmission and decoding latency as
described in 5.3.3.
A.2 Guidelines
The following guidelines should be taken into account.
a) Receivers which receive an indication in the data-burst-dependent information that
signals the presence of MPS, but that are not capable of decoding MPS, should not
refuse decoding of that stream. It is highly recommended that non-MPS capable decoders
decode just the AAC LC / HE AAC channel configuration as indicated by the downmix
codec configuration record and ignore the MPS extension in the bit stream.
b) The IEC 60958 frame rate may be calculated by making use of the audio sampling rate
indication from the AudioSpecificConfig inside the LATM StreamMuxConfig. It is highly

 IEC 2018
recommended that the correct codec indication as well as the matching sampling

frequency or IEC 60958 frame rate indication is available before starting transmission of

IEC 61937-11 data bursts. In case of signaled audio configuration changes upstream it is

highly recommended that audio data-bursts referring to the new program are only

transmitted after the relevant information (new codec and new sampling frequency) is

available to the transmitter and signaled properly.

c) It is highly recommended that decoders do not attempt to decode an audio stream before

they have received the corresponding decoder configuration records (e.g.

AudioSpecificConfig).
– 16 – IEC 61937-11:2010+AMD1:2018 CSV

 IEC 2018
Annex B
(normative)
High-speed transmission
B.1 Indication
Typically, the transmitting interface frame rate equals the sampling frequency for the

IEC 61937-11 protocol. In the case of a mismatch, IEC 61937-11 uses channel status fields to

identify their relationship as shown in Table B.1 and the following scheme.

Table B.1 – Indication fields
Mode 0 Channel status IEC 60958-3 (LPCM) IEC 61937-11 (MPEG-4 AAC)
Bit 24 to 27 Sampling frequency IEC 60958 frame rate
Bit 30 to 31 Sampling frequency extension
Bit 36 to 39 Original sampling frequency
Bit 44 to 47 Audio sampling frequency coefficient

The "original sampling frequency" identifies reproduction frequency after decoding the
IEC 61937-11 bitstream. The IEC 61937-11 bitstream is transmitted at "IEC 60958 frame rate".
The "audio sampling frequency coefficient" optionally shows the relationship between
"IEC 60958 frame rate" and "original sampling frequency" as follows.
IEC 60958 frame rate = (original sampling frequency) × (audio sampling frequency coefficient)
Values of these fields are given in IEC 60958-3.
IEC 61937-11 uses clock accuracy carried on channel status bits 28 and 29 of the
IEC 60958-3 definitions for accuracy of the interface frame rate. The value of "1 1" (interface
frame rate not matched to sampling frequency) stands for the condition that the actual
interface frame rate in transmitting is not matching the logical IEC 60958 frame rate.
B.2 Example
Table B.2 shows an example that has a 96-kHz interface frame rate and 48-kHz reproduction
frequency.
Table B.2 – Signalling example
IEC 60958 frame rate Original sampling frequency Audio sampling frequency
coefficient
"0 1 0 1 0 0" (96 kHz) "1 0 1 1" (48 kHz) "1 1 1 1" (×2) or
"0 0 0 0" (No indication)
 IEC 2018
Bibliography
IEC 61937 (all parts), Digital audio – Interface for non-linear PCM encoded audio bitstreams

applying IEC 60958
IEC 61937-6, Digital audio – Interface for non-linear PCM encoded audio bitstreams

applying IEC 60958 – Part 6: Non-linear PCM bitstreams according to the MPEG-2 AAC and

MPEG-4 AAC audio formats
IEC 61937-10, Digital audio – Interface for non-linear PCM encoded audio bitstreams applying

IEC 60958 – Part 10: Non-linear PCM bitstreams according to the MPEG-4 Audio Lossless

Coding (ALS) format (under consideration)
ISO/IEC 13818-1, Information technology – Generic coding of moving pictures and
associated audio information – Part 1: Systems
ISO/IEC 13818-7, Information technology – Generic coding of moving pictures and
associated audio information – Part 7: Advanced Audio Coding (AAC)
ISO/IEC 23003-1:2007, Information technology – MPEG audio technologies – Part 1: MPEG
Surround
ARIB STD B-32, Video coding, audio coding, and multiplexing specifications for digital
broadcasting
Rec. ITU-R BS.2051-0, Advanced sound system for programme production

_____________
—————————
NOTE Technical corrigendum 1 from 2008 has to be applied.

IEC 61937-11 ®
Edition 1.1 2018-11
CONSOLIDATED VERSION
FINAL VERSION
Digital audio – Interface for non-linear PCM encoded audio bitstreams applying
IEC 60958 –
Part 11: MPEG-4 AAC and its extensions in LATM/LOAS

– 2 – IEC 61937-11:2010+AMD1:2018 CSV

 IEC 2018
CONTENTS
FOREWORD . 3

INTRODUCTION . 5

INTRODUCTION to Amendment 1 . 5

1 Scope . 6

2 Normative references . 6

3 Terms, definitions and abbreviations . 6

3.1 Terms and definitions . 6
3.2 Abbreviations . 8
4 Mapping of the audio bit stream on to IEC 61937-1 . 8
4.1 General . 8
4.2 Burst-info for MPEG-4 AAC and its extensions in LATM/LOAS . 8
5 Format of data-burst for MPEG-4 AAC and its extensions in LATM/LOAS . 9
5.1 General . 9
5.2 Pause data-bursts for MPEG-4 AAC and its extensions in LATM/LOAS . 9
5.3 Audio data-bursts . 10
5.3.1 MPEG-4 AAC and its extensions in LATM/LOAS . 10
5.3.2 LATM/LOAS framing . 12
5.3.3 Latency . 12
Annex A (informative) Calculation of delay and data-burst repetition rates – guidelines . 14
Annex B (normative) High-speed transmission . 16
Bibliography . 17

Figure 1 – Data-burst structure . 10
Figure 2 – Latency diagram for burst reception and decoding . 13

Table 1 – Values for data-type bits 0-4 and data-type bits 5-6 . 9
Table 2 – Repetition period of pause data-bursts . 9
Table 3 – Data-type-dependent information . 11
Table A.1 – Examples – Calculation of delay and data-burst repetition rates . 14
Table B.1 – Indication fields . 16

Table B.2 – Signalling example . 16

 IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
DIGITAL AUDIO –
INTERFACE FOR NON-LINEAR PCM ENCODED

AUDIO BITSTREAMS APPLYING IEC 60958 –

Part 11: MPEG-4 AAC and its extensions 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 ac
...

IEC 61937-11 ®
Edition 1.0 2010-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Digital audio – Interface for non-linear PCM encoded audio bitstreams applying
IEC 60958 –
Part 11: MPEG-4 AAC and its extensions in LATM/LOAS

Audionumérique – Interface pour les flux de bits audio à codage MIC non
linéaire conformément à la CEI 60958 –
Partie 11: MPEG-4 AAC et ses extensions en LATM/LOAS

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IEC 61937-11 ®
Edition 1.0 2010-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Digital audio – Interface for non-linear PCM encoded audio bitstreams applying
IEC 60958 –
Part 11: MPEG-4 AAC and its extensions in LATM/LOAS

Audionumérique – Interface pour les flux de bits audio à codage MIC non linéaire
conformément à la CEI 60958 –
Partie 11: MPEG-4 AAC et ses extensions en LATM/LOAS

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX P
ICS 33.160.30; 33.170 ISBN 978-2-88912-321-6
– 2 – 61937-11  IEC:2010
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and abbreviations . 6
3.1 Terms and definitions . 6
3.2 Abbreviations . 8
4 Mapping of the audio bit stream on to IEC 61937-1 . 8
4.1 General . 8
4.2 Burst-info for MPEG-4 AAC and its extensions in LATM/LOAS . 8
5 Format of data-burst for MPEG-4 AAC and its extensions in LATM/LOAS . 9
5.1 General . 9
5.2 Pause data-bursts for MPEG-4 AAC and its extensions in LATM/LOAS . 9
5.3 Audio data-bursts . 10
5.3.1 MPEG-4 AAC and its extensions in LATM/LOAS . 10
5.3.2 LATM/LOAS framing . 12
5.3.3 Latency . 12
Annex A (informative) Calculation of delay and data-burst repetition rates – guidelines . 14
Bibliography . 16

Figure 1 – Data-burst structure . 10
Figure 2 – Latency diagram for burst reception and decoding . 13

Table 1 – Values for data-type and sub-data-type . 9
Table 2 – Repetition period of pause data-bursts . 9
Table 3 – Data-type-dependent information . 11
Table A.1 – Examples – Calculation of delay and data-burst repetition rates . 14

61937-11  IEC:2010 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DIGITAL AUDIO –
INTERFACE FOR NON-LINEAR PCM ENCODED
AUDIO BITSTREAMS APPLYING IEC 60958 –

Part 11: MPEG-4 AAC and its extensions 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
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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6) All users should ensure that they have the latest edition of this publication.
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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.
International Standard IEC 61937-11 has been prepared by technical area 4: Digital system
interfaces and protocols, of IEC technical committee 100: Audio, video and multimedia
systems and equipment.
This bilingual version, published in 2011-02, corresponds to the English version.
The text of this standard is based on the following documents:
CDV Report on voting
100/1491/CDV 100/1580/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.

– 4 – 61937-11  IEC:2010
The French version of this standard has not been voted upon.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of IEC 61937, under the general title Digital audio – Interface for non-linear
PCM encoded audio bitstreams applying IEC 60958 can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
61937-11  IEC:2010 – 5 –
INTRODUCTION
Modern digital video broadcasting standards such as DVB include support for the MPEG-4
HE AAC and/or HE AAC v2 audio codecs as 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) audio codecs introduce new features and
capabilities that require a framing format that supports more flexible signaling and delivery
mechanisms. Therefore, MPEG-2 Systems (ISO/IEC 13818-1) specifies 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 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.
– 6 – 61937-11  IEC:2010
DIGITAL AUDIO –
INTERFACE FOR NON-LINEAR PCM ENCODED
AUDIO BITSTREAMS APPLYING IEC 60958 –

Part 11: MPEG-4 AAC and its extensions in LATM/LOAS

1 Scope
This part of IEC 61937 describes the method to convey non-linear PCM bitstreams encoded
according to the MPEG-4 AAC format and its extensions spectral band replication, parametric
stereo and MPEG surround, framed in MPEG-4 LATM/LOAS.
2 Normative references
The following referenced documents are indispensable for the application 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 (all parts), Digital audio interface
IEC 61937-1, Digital audio – Interface for non-linear PCM encoded audio bitstreams
applying IEC 60958 – Part 1: General
IEC 61937-2, Digital audio – Interface for non-linear PCM encoded audio bitstreams
applying IEC 60958 – Part 2: Burst-info
ISO/IEC 14496-3:2009, Information technology – Coding of audio-visual objects – Part 3:
Audio
3 Terms, definitions and abbreviations
For the purposes of this document the terms, definitions and abbreviations of IEC 61937-1,
IEC 61937-2 and the following apply.
3.1 Terms and definitions
3.1.1
access unit
smallest entity to which timing information can be attributed; an access unit is the smallest
individually decodable unit; a decoder consumes access units
3.1.2
AudioMuxElement(1)
LATM element that carries payload data for at least one audio elementary stream, related
payload length information and multiplex configuration information
NOTE This element carries payload data in form of PayloadMux elements. The number in brackets indicates
multiplexing configuration (StreamMuxConfig) is multiplexed into AudioMuxElements, that is in-band transmission.
3.1.3
AudioSpecificConfig
configuration structure used to convey parameters to initialize the MPEG-4 audio decoder

61937-11  IEC:2010 – 7 –
3.1.4
low overhead MPEG-4 audio transport multiplex
LATM
multiplexing layer defined by ISO/IEC 14496-3; used for multiplexing of audio elementary
streams
3.1.5
low overhead audio stream
LOAS
synchronisation layer defined by ISO/IEC 14496-3; 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; 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 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 For further information please refer to 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 The MPEG-4 high efficiency AAC profile version 2 is a superset of the MPEG-4 high efficiency AAC profile.
3.1.9
MPEG surround
technology used for coding of multichannel signals based on a downmixed signal of the
original multichannel signal, and associated spatial parameters
NOTE MPEG surround is defined in ISO/IEC 23003-1.
3.1.10
PayloadMux
payload data chunk in an AudioMuxElement that contains potentially multiplexed payload data
for multiple audio elementary streams; in general PayloadMux elements can be concatenated
inside AudioMuxElements
3.1.11
SpatialSpecificConfig
configuration structure used to initialize the MPEG surround decoder
3.1.12
StreamMuxConfig
configuration structure that describes the structure of the LATM payload multiplex

– 8 – 61937-11  IEC:2010
3.1.13
Sub-data-type
reference to the type of payload of the data-bursts defined for the use with the specified data-
type
3.1.14
modified discrete cosine transformation
MDCT
transformation schema used by AAC
3.1.15
transformation length (of the AAC codec or core codec)
AAC can operate in two modes using either a 960 lines or 1 024 lines MDCT transformation
for long blocks; an MDCT line is a spectral component described by frequency, amplitude and
phase
3.2 Abbreviations
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
PNS Perceptual Noise Substitution
PS Parametric Stereo
SBR Spectral Band Replication
TL 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 in LATM/LOAS
The 16-bit burst-info contains information about the data which will be found in the data-burst
(see Table 1).
61937-11  IEC:2010 – 9 –
Table 1 – Values for data-type and sub-data-type
Data-type
according to Sub-data-type
Repetition period
Reference
IEC 61937-2
Contents of data-bursts
Value of Pc
point R
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 Definition specific to
IEC 61937-10 IEC 61937-10
1 AAC LC Bit 0 of Pa  960 / 1 024
2 HE AAC Bit 0 of Pa 1 920 / 2 048
3 Reserved for future reserved Reserved for future definition
definition of other of other applications
applications
24–31 0–3 According to IEC 61937
Bits 0–4 of the burst-info (Pc) signal the data-type used for transmission. For MPEG-4 AAC-based audio in
LATM/LOAS, the signaled data-type is 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.
5 Format of data-burst for MPEG-4 AAC and its extensions in LATM/LOAS
5.1 General
This clause specifies the data-burst for MPEG-4 AAC audio and its extensions in LATM/LOAS.
Specific properties such as reference points, repetition period, the method of filling stream
gaps and decoding latency are specified.
The decoding latency (or delay), indicated for the sub-data-types, 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
Sub-data-type for MPEG-4 audio in LATM/LOAS
— 64 IEC 60958 frames
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 according to 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 may not be
an integer multiple of 64 IEC 60958 frames.

– 10 – 61937-11  IEC:2010
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 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.

MPEG-4 LOAS framed MPEG-4 LOAS framed
Pa Pb Pc Pd Pa Pb Pc Pd
burst payload burst payload
Bit 0 of Pa Bit 0 of Pa
MPEG-4 LOAS frame Stuffing MPEG-4 LOAS frame
Burst repetition period
IEC  1057/10
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 P – P measured in bits)
AD
AD A D
B = 4 × 16 bit  (B is the size of the burst spacing measured in bits)
S
S
TL = 1 024 or 960 lines (TL is the used MDCT transformation length in MDCT lines)
The maximum data-burst payload size for AAC not utilizing SBR is calculated according to the
following equation:
+ B ) = maximum payload size in bits.
2 × 16 bit × TL – ( P
AD S
If HE AAC is used the maximum data-burst payload size is calculated according to the
following equation:
4 × 16 bit × TL – ( P + B ) = maximum payload size in bits.
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.
61937-11  IEC:2010 – 11 –
Table 3 – Data-type-dependent information
Bits of Pc
Value Definition Description
LSB…MSB
8 0 AAC Transformation Length 1 024 lines
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 signaling)
2 Embedded MPS data present / explicit signaling 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
signaled by the sub-data-type to calculate the data-burst repetition period. Receivers shall
read the sub-data-types 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 stream.
The two Pc bits 10–11 indicate the presence and transport configuration of MPS data in the
encoded audio stream. The value 0 indicates that no MPS data is present. Values 1 and 2
indicate that MPS data is present in the audio bit stream. Pc bits 10-11 signaling 1 indicates
that the MPS payload as well as the MPS SpatialSpecificConfig is embedded inside the
payload of the first LATM layer which conveys the AAC LC or HE AAC data stream. Pc bits
10–11 signaling 2 indicates that the MPS payload is also embedded inside the payload of the
first layer. But in this case the MPS SpatialSpecificConfig is signaled explicitly associated to
the second layer inside the LATM StreamMuxConfig. The value 3 signaled by the Pc bits 10–
11 is reserved for future use.
This specification does not allow the transmission of MPS payload which is not embedded
inside the AAC LC or HE AAC payload but resides separated from the AAC LC or HE AAC
payload inside another LATM layer.
The presence of the PS or MPS extensions does not influence the data-burst repetition rate or
the calculation of the transmission and decoding latency as described in 5.3.3.
The Pc bit 12 is reserved for future use. This bit shall be set to 0.
One complete AAC access unit represents a time interval of 1 024 or 960 audio samples
embedded into the data-burst payload. When transmitting MPEG-4 HE AAC encoded audio
programs, SBR is used as an extension to AAC. In this case the sampling frequency of the
MPEG-4 AAC core component is usually half the sampling frequency of the SBR tool and
audio program. One complete HE AAC access unit represents a time interval of 2 048 or
1 920 audio samples embedded into the data-burst payload.

– 12 – 61937-11  IEC:2010
HE AAC bit streams with downsampled SBR shall be transmitted signaling AAC LC in the sub-
data-type. Therefore one access unit corresponds to 1 024 or 960 AAC encoded audio
samples.
If HE AAC is signaled by the sub-data-type the IEC 60958 frame rate shall be equal to the
sampling frequency of the SBR tool. If AAC LC is signaled the IEC 60958 frame rate shall
correspond to the sampling frequency of AAC.
The reference point of a data-burst is bit 0 of Pa and occurs exactly once every number of
IEC 60958 sampling periods which is computed using the information from Table 1 and
Table 3. The data-burst containing one LATM/LOAS audio frame shall occur at a constant rate.
The intervals for data-bursts sharing the same bit-stream-number shall correspond exactly to
the amount of IEC 60958 frames which is calculated using the information from Table 1 and
Table 3.
It is not allowed to transmit audio data streams using IEC 60958 frame rates below 32 kHz.
5.3.2 LATM/LOAS framing
The LOAS frame as described in ISO/IEC 14496-3 shall be mapped directly to the payload
section, right after the preamble words of the data-burst. The first bit of the LOAS frame shall
always correspond to the first bit after the preamble section in the data-burst.
The payload in a data-burst consists of one complete LOAS frame containing one LATM
AudioMuxElement. It is not allowed to convey one LATM/LOAS frame using multiple data-
bursts. LOAS frames exceeding the payload capacity of a data-burst shall be dropped and the
actual data-burst shall be replaced by a sequence of pause-bursts to match the duration of
that data-burst.
The parameter numSubFrames from the LATM StreamMuxConfig shall be 0. The parameter
numProgram from the LATM StreamMuxConfig shall be 0. The parameter numLayer from the
LATM StreamMuxConfig shall be 0 except for audio streams signaling the availability of MPS
with payload embedding and explicit signaling of MPS in the second LATM layer. In such
cases the presence of a second layer in LATM frames is allowed and therefore numLayer
shall be 1 indicating 2 layers. In this configuration there exists no payload associated to the
second LATM layer and therefore the payload size indication for the second layer in LATM is
set to zero.
Only the LOAS AudioSyncStream() scheme shall be used in the context of this specification.
The LATM StreamMuxConfig structure shall be conveyed inside the LATM multiplex. This is
the main structure that is utilized by the decoder for configuration. The StreamMuxConfig may
not be present in each LATM frame in order to save bandwidth. It may be sent in intervals to
allow decoders to tune in to a running stream.
5.3.3 Latency
The latency of an external audio decoder to decode MPEG-4 AAC and its extensions in
LATM/LOAS is defined as the sum of the receiving time of the audio payload in one data-burst
and the time used for decoding of one access unit.
Each data-burst contains a minimum of 4 stuffing words (Pz of 16 bits). The repetition period
of data-bursts in IEC 60958 frames is computed according to information from Table 1 and
Table 3. The reception delay for one audio access unit is calculated as the time elapsed
counting from the first bit of the data-burst until the last bit of the actual audio payload inside
the data-burst received. Subsequent stuffing is not taken into account. After a complete frame
is received immediate decoding and subsequent rendering of the audio frame is not
recommended as the size of the next audio frame and therefore time required for receiving it
completely cannot be determined accurately.

61937-11  IEC:2010 – 13 –
In order to simplify the timing mechanism for receiving and decoding of content of data-bursts,
the receiving delay should be calculated as the time necessary to receive the complete data-
burst including the stuffing. The maximum time available to decode (the decoding delay)
should be selected to correspond to the length of one full data-burst. This results in an overall
delay corresponding to two complete data-bursts for reception and decoding.
For synchronisation (for example with video), the recommended value for latency corresponds
to the time necessary to receive two complete data-bursts. Figure 2 shows the simplified and
recommended method for calculating the latency for reception and decoding.
A shorter latency may be acceptable if synchronisation is not required.

LOAS framed LOAS framed
Pa Pb Pc Pd Pa Pb Pc Pd Pa
burst payload burst payload
Bit 0 of Pa Bit 0 of Pa
Stuffing
LOAS frame LOAS frame
Stuffing
Burst repetition period
Receiving delay Decoding delay
Latency of receiving and decoding
IEC  1058/10
NOTE This diagram shows the recommended method.
Figure 2 – Latency diagram for burst reception and decoding

– 14 – 61937-11  IEC:2010
Annex A
(informative)
Calculation of delay and data-burst repetition rates – guidelines

A.1 Examples
Some examples for the calculation of data-burst-repetition rates and latencies can be found in
Table A.1.
Table A.1 – Examples – Calculation of delay and data-burst repetition rates
Data-burst
Bit 8 of Pc AAC sampling SBR sampling IEC 60958 Overall
Bits 5-6
repetition rate
TL rate rate frame rate latency
of Pc codec
IEC 60958
indication
lines kHz kHz kHz ms
frames
32 n/a 32 64
1 024 44,1 n/a 44,1 1 024 46,44
48 n/a 48 42,67
96 n/a 96 21,33
AAC LC
32 n/a 32 60
44,1 n/a 44,1 43,54
960 960
48 n/a 48 40
96 n/a 96 20
16 32 32 128
22,05 44,1 44,1 2 048 92,88
1 024
24 48 48 85,33
48 96 96 42,67
HE AAC
16 32 32 120
960 22,05 44,1 44,1 1 920 87,07

24 48 48 80
48 96 96 40
The presence of the PS or MPS extensions signaled by Pc bits 9–11 does not influence the
data-burst repetition rate or the calculation of the transmission and decoding latency as
described in 5.3.3.
A.2 Guidelines
The following guidelines should be taken into account.
a) Receivers which receive an indication in the data-burst-dependent information that
signals the presence of MPS, but that are not capable of decoding MPS, should not
refuse decoding of that stream. It is highly recommended that non-MPS capable decoders
decode just the AAC LC / HE AAC channel configuration as indicated by the downmix
codec configuration record and ignore the MPS extension in the bit stream.
b) The IEC 60958 frame rate may be calculated by making use of the audio sampling rate
indication from the AudioSpecificConfig inside the LATM StreamMuxConfig. It is highly

61937-11  IEC:2010 – 15 –
recommended that the correct codec indication as well as the matching sampling
frequency or IEC 60958 frame rate indication is available before starting transmission of
IEC 61937-11 data bursts. In case of signaled audio configuration changes upstream it is
highly recommended that audio data-bursts referring to the new program are only
transmitted after the relevant information (new codec and new sampling frequency) is
available to the transmitter and signaled properly.
c) It is highly recommended that decoders do not attempt to decode an audio stream before
they have received the corresponding decoder configuration records (e.g.
AudioSpecificConfig).
– 16 – 61937-11  IEC:2010
Bibliography
IEC 61937 (all parts), Digital audio – Interface for non-linear PCM encoded audio bitstreams
applying IEC 60958
IEC 61937-6, Digital audio – Interface for non-linear PCM encoded audio bitstreams
applying IEC 60958 – Part 6: Non-linear PCM bitstreams according to the MPEG-2 AAC and
MPEG-4 AAC audio formats
IEC 61937-10, Digital audio – Interface for non-linear PCM encoded audio bitstreams applying
IEC 60958 – Part 10: Non-linear PCM bitstreams according to the MPEG-4 Audio Lossless
Coding (ALS) format (under consideration)
ISO/IEC 13818-1, Information technology – Generic coding of moving pictures and
associated audio information – Part 1: Systems
ISO/IEC 13818-7, Information technology – Generic coding of moving pictures and
associated audio information – Part 7: Advanced Audio Coding (AAC)
ISO/IEC 23003-1:2007, Information technology – MPEG audio technologies – Part 1: MPEG
Surround
_____________
—————————
NOTE Technical corrigendum 1 from 2008 has to be applied.

– 18 – 61937-11  CEI:2010
SOMMAIRE
AVANT-PROPOS . 19
INTRODUCTION . 21
1 Domaine d’application . 22
2 Références normatives . 22
3 Termes, définitions et abréviations . 22
3.1 Termes et définitions . 22
3.2 Abréviations . 24
4 Cartographie du flux de bits audio avec la CEI 61937-1 . 25
4.1 Généralités. 25
4.2 Info-de-salve pour le profil MPEG-4 AAC et ses extensions en LATM/LOAS . 25
5 Format de la salve de données pour le profil MPEG-4 AAC et ses extensions en
LATM/LOAS . 25
5.1 Généralités. 25
5.2 Salves de données " pause" pour le profil MPEG-4 AAC et ses extensions en
LATM/LOAS" . 25
5.3 Salves de données audio . 26
5.3.1 MPEG-4 AAC et ses extensions en LATM/LOAS . 26
5.3.2 Trames LATM/LOAS . 28
5.3.3 Temps de latence . 29
Annexe A (informative) Calcul du retard et des taux de répétition des salves de
données – lignes directrices . 30
Bibliographie . 32

Figure 1 – Structure d'une salve de données . 26
Figure 2 – Diagramme du temps de latence pour la réception et le décodage d’une
salve . 29

Tableau 1 – Valeurs pour les types de données et les sous-types de données. 25
Tableau 2 – Période de répétition des salves de données "pause" . 26
Tableau 3 – Informations dépendant du type-de-données . 27
Tableau A.1 – Exemples – Calcul du retard (ou temps de latence) et des taux de
répétition des salves de données . 30

61937-11  CEI:2010 – 19 –
COMMISSION ÉLECTROTECHNIQUE INTERNATIONALE
____________
AUDIONUMÉRIQUE –
INTERFACE POUR LES FLUX DE BITS AUDIO À CODAGE MIC
NON LINÉAIRE CONFORMÉMENT À LA CEI 60958 –

Partie 11: MPEG-4 AAC et ses extensions en LATM/LOAS

AVANT-PROPOS
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selon des conditions fixées par accord entre les deux organisations.
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de brevets et de ne pas avoir signalé leur existence.
La Norme internationale CEI 61937-11 a été établie par le domaine technique 4: Interfaces et
protocoles pour les systèmes numériques, du comité d’études 100 de la CEI: Systèmes et
appareils audio, vidéo et multimédia.
La présente ver
...