ISO/IEC 14496-14:2018

INTERNATIONAL ISO/IEC
STANDARD 14496-14
Second edition
2018-11
Information technology — Coding of
audio-visual objects —
Part 14:
MP4 file format
Technologies de l'information — Codage des objets audiovisuels —
Partie 14: Format de fichier MP4
Reference number
©
ISO/IEC 2018
© ISO/IEC 2018
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ii © ISO/IEC 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Storage of MPEG-4 . 1
4.1 Elementary stream tracks . 1
4.1.1 Elementary stream data . 1
4.1.2 Elementary stream descriptors . 2
4.1.3 Object descriptors . 2
4.2 Track identifiers . 3
4.3 Synchronization of streams . 4
4.4 Composition . 5
4.5 Handling of M4Mux . 5
5 File identification . 7
6 Additions to the Base Media Format . 7
6.1 General . 7
6.2 Object Descriptor Box . 7
6.2.1 Description . . . 7
6.2.2 Syntax . 8
6.2.3 Semantics . 8
6.3 Track reference types . 8
6.4 Track header box . 8
6.5 Handler reference types . 8
6.6 MPEG-4 media header boxes . 9
6.6.1 General. 9
6.6.2 Syntax . 9
6.6.3 Semantics . 9
6.7 Sample description boxes . 9
6.7.1 Description . . . 9
6.7.2 Syntax .10
6.7.3 Semantics .11
6.8 Degradation priority values .12
7 Template fields used .12
Annex A (informative) Handling of audio timestamps and profile/level indication .13
Bibliography .14
© ISO/IEC 2018 – All rights reserved iii

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. 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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for
the different types of document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 29, Coding of audio, picture, multimedia and hypermedia information.
This second edition cancels and replaces the first edition (ISO/IEC 14496-14:2003), which has been
technically revised.
The main changes compared to the previous edition are the incorporation of ISO/IEC 14496-14:2003/
Cor.1:2006 and ISO/IEC 14496-14:2003/Amd.1:2010 as well as some minor editorial changes.
A list of all parts in the ISO/IEC 14496 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO/IEC 2018 – All rights reserved

Introduction
This document defines MP4 as an instance of the ISO Media File format (ISO/IEC 14496-12).
The general nature of the ISO Media File format is fully exercised by MP4. MPEG-4 presentations can be
highly dynamic, and there is an infrastructure — the Object Descriptor Framework — which serves to
manage the objects and streams in a presentation. An Initial Object Descriptor serves as the starting
point for this framework. In the usage modes documented in the ISO Media File, an Initial Object
Descriptor would normally be present, as shown in the following diagrams.
Figure 1 gives an example of a simple interchange file, containing two streams.
Figure 1 — Simple interchange file
In Figure 2, a set of files being used in the process of content creation is shown.
Figure 2 — Content creation file
Figure 3 shows a presentation prepared for streaming over a multiplexing protocol, only one hint track
is required.
© ISO/IEC 2018 – All rights reserved v

Figure 3 — Hinted presentation for streaming
The International Organization for Standardization (ISO) and International Electrotechnical
Commission draw attention to the fact that it is claimed that compliance with this document may
involve the use of patents.
ISO and IEC take no position concerning the evidence, validity and scope of these patent rights.
The holder of these patent rights has assured ISO and IEC that he/she is willing to negotiate licences
under reasonable and non-discriminatory terms and conditions with applicants throughout the
world. In this respect, the statement of the holder of this patent right is registered with ISO and IEC.
Information may be obtained from:
Apple, Inc.
1 Infinite Loop MS 3-PAT
US-Cupertino
CA 95014-2084
USA
TDVision Systems, Inc.
8001 Irvine Center Drive, Suite 400
Irvine, CA. 92618
USA
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights other than those identified above. ISO and IEC shall not be held responsible for identifying
any or all such patent rights.
vi © ISO/IEC 2018 – All rights reserved

INTERNATIONAL STANDARD ISO/IEC 14496-14:2018(E)
Information technology — Coding of audio-visual
objects —
Part 14:
MP4 file format
1 Scope
This document defines the MP4 file format, as derived from the ISO Base Media File format.
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.
ISO/IEC 14496-1:2010, Information technology — Coding of audio-visual objects — Part 1: Systems
ISO/IEC 14496-12:2015, Information technology — Coding of audio-visual objects — Part 12: ISO Base
Media File Format
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 14496-12 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
4 Storage of MPEG-4
4.1 Elementary stream tracks
4.1.1 Elementary stream data
To maintain the goals of streaming protocol independence, the media data is stored in its most ‘natural’
format, and not fragmented. This enables easy local manipulation of the media data. Therefore media-
data is stored as access units, a range of contiguous bytes for each access unit (a single access unit is the
definition of a ‘sample’ for an MPEG-4 media stream). This greatly facilitates the fragmentation process
used in hint tracks. The file format can describe and use media data stored in other files, however this
restriction still applies. Therefore if a file is to be used which contains ‘pre-fragmented’ media data (e.g.
an M4Mux stream on disc), the media data will need to be copied to re-form the access units, in order to
import the data into this file format.
This is true for all stream types in this specification, including such ‘meta-information’ streams as
Object Descriptor and the Clock Reference. The consequences of this are, on the positive side, that the
file format treats all streams equally; on the negative side, this means that there are ‘internal’ cross-
links between the streams. This means that adding and removing streams from a presentation will
© ISO/IEC 2018 – All rights reserved 1

involve more than adding or deleting the track and its associated media-data. Not only is it necessary
that the stream be placed in, or removed from, the scene, the object descriptor stream might also need
updating.
For each track the entire ES-descriptor is stored as the sample description or descriptions.
The SLConfigDescriptor for the media track shall be stored in the file using a default value
(predefined = 2), except when the Elementary Stream Descriptor refers to a stream through a URL, i.e.
the referred stream is outside the scope of the MP4 file. In that case the SLConfigDescriptor is not
constrained to this predefined value.
In a transmitted bitstream, the access units in the SL Packets are transmitted on byte boundaries. This
means that hint tracks will construct SL Packet headers using the information in the media tracks, and
the hint tracks will reference the access units from the media track. The placement of the header during
hinting is possible without bit shifting, as each SL Packet and corresponding contained access unit will
both start on byte boundaries.
4.1.2 Elementary stream descriptors
The ESDescriptor for a stream within the scope of the MP4 file as described in this document is stored
in the sample description and the fields and included structures are restricted as follows:
— ES_ID - set to 0 as stored; when built into a stream, the lower 16 bits of the TrackID are used.
— streamDependenceFlag – set to 0 as stored; if a dependency exists, it is indicated using a track
reference of type 'dpnd'.
— URLflag – kept untouched, i.e.: set to false, as the stream is in the file, not remote.
— SLConfigDescriptor – is predefined type 2.
— OCRStreamFlag – set to false in the file.
The ESDescriptor for a stream referenced through an ES URL is stored in the sample description and
the fields and included structures are restricted as follows:
— ES_ID – set to 0 as stored; when built into a stream, the lower 16 bits of the TrackID are used.
— streamDependenceFlag – set to 0 as stored; if a dependency exists, it is indicated using a track
reference of type 'dpnd'.
— URLflag – kept untouched, i.e.: set to true, as the stream is not in the file.
— SLConfigDescriptor – kept untouched.
— OCRStreamFlag – set to false in the file.
Note that the QoSDescriptor may also need re-writing for transmission as it contains information
about PDU sizes, etc.
4.1.3 Object descriptors
The initial object descriptor and object descriptor streams are handled specially within the file
format. Object descriptors contain ES descriptors, which in turn contain stream specific information.
In addition, to facilitate editing, the information about a track is stored as an ESDescriptor in the
sample description within that track. It shall be taken from there, re-written as appropriate, and
transmitted as part of the OD stream when the presentation is streamed.
As a consequence, ES descriptors are not stored within the OD track or initial object descriptor. Instead,
the initial object descriptor has a descriptor used only in the file, containing solely the track ID of the
elementary stream. When used, an appropriately re-written ESDescriptor from the referenced
track replaces this descriptor. Likewise, OD tracks are linked to ES tracks by track references. Where
2 © ISO/IEC 2018 – All rights reserved

an ESdescriptor would be used within the OD track, another descriptor is used, which again occurs
only in the file. It contains the index into the set of mpod track references that this OD track owns. A
suitably re-written ESDescriptor replaces it by the hinting of this track.
The ES_ID_Inc is used in the Object Descriptor Box:
class ES_ID_Inc extends BaseDescriptor : bit(8) tag=ES_IDIncTag {
unsigned int(32)  Track_ID;  // ID of the track to use
}
ES_ID_IncTag = 0x0E is reserved for file format usage.
The ES_ID_Ref is used in the OD stream:
class ES_ID_Ref extends BaseDescriptor : bit(8) tag=ES_IDRefTag {
bit(16)  ref_index;  // track ref. index of the track to use
}
ES_ID_RefTag = 0x0F is reserved for file format usage.
MP4_IOD_Tag = 0x10 is reserved for file format usage.
MP4_OD_Tag = 0x11 is reserved for file format usage.
IPI_DescrPointerRefTag = 0x12 is reserved for file format usage.
ES_DescrRemoveRefTag = 0x07 is reserved for file format usage (command tag).
NOTE The above tag values are defined in ISO/IEC 14496-1:2010, 7.2.2.1 and 7.2.2.3.2 (Tables 1 and 2), and
the actual values are referenced from those tables.
A hinter may need to send more OD events than actually occur in the OD track: for example, if the ES_
description changes at a time when there is no event in the OD track. In general, any OD events explicitly
authored into the OD track should be sent along with those necessary to indicate other changes. The ES
descriptor sent in the OD track is taken from the description of the temporally next sample in the ES
track (in decoding time).
4.2 Track identifiers
The track identifiers used in an MP4 file are unique within that file; no two tracks may use the same
identifier.
Each elementary stream in the file is stored as a media track. In the case of an elementary stream, the
lower two bytes of the four-byte track_ID shall be set to the elementary stream identifier (ES_ID);
the upper two bytes of the track_ID are zero in this case. Hint tracks may use track identifier values in
the same range, if this number space is adequate (which it generally is). However, hint track identifiers
may also use larger values of track identifier, as their identifiers are not mapped to elementary stream
identifiers. Thus very large presentations may use the entire 16-bit number space for elementary
stream identifiers.
The next track identifier value, found in next_track_ID in the MovieHeaderBox, as defined in the ISO
Base Media Format, generally contains a value one greater than the largest track identifier value found
in the file. This enables easy generation of a track identifier under most circumstances. However, if this
value is equal to or larger than 65535, and a new media track is to be added, then a search in the file is
needed for a free track identifier. If the value is all 1s (32-bit maxint) then this search is needed for all
additions.
If it is desired to add a track with a known track identifier (elementary stream identifier) then it is
necessary to search to ensure that there is no conflict. Note that hint tracks can be re-numbered fairly
© ISO/IEC 2018 – All rights reserved 3

easily while more care should be taken with media tracks, as there may be references to their ES_ID
(track ID) in other tracks.
If hint tracks have track IDs outside the allowed range for elementary stream tracks, then next track ID
documents the next available hint track ID. Since this is larger than 65535, a search will then always be
needed to find a valid elementary stream track ID.
If two presentations are merged, then there may be conflict between their track IDs. In that case, one or
more tracks will have to be re-numbered. There are two actions to be taken here:
— Changing the ID of the track itself, which is easy (track ID in the trac
...