ISO/IEC 23001-7:2023/FDAmd 1

• Status: Not Published
• ICS: 35.040.40 - Coding of audio, video, multimedia and hypermedia information
• Technical Committee: ISO/IEC JTC 1/SC 29 - Coding of audio, picture, multimedia and hypermedia information
• Drafting Committee: ISO/IEC JTC 1/SC 29/WG 3 - MPEG Systems
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 25-Aug-2026
• Completion Date: 25-Aug-2026

• Amends: ISO/IEC 23001-7:2023 - Information technology — MPEG systems technologies — Part 7: Common encryption in ISO base media file format files
• Effective Date: 10-May-2025

ISO/IEC 23001-7:2023/FDAmd 1 is an ISO amendment to Part 7 of the MPEG systems technologies series for common encryption in ISO base media file format files. It adds support for AES-256 and updates the signaling used by files, tracks and readers so implementations can handle 128-bit or 256-bit protection schemes in a consistent way.

What does ISO/IEC 23001-7:2023/FDAmd 1 specify?

ISO/IEC 23001-7:2023/FDAmd 1 keeps the focus on encrypting elementary stream data in media samples inside ISO base media file format files. It updates the encryption scope, the TrackEncryptionBox signaling, the AES-CTR and AES-CBC scheme text, the version rules for encryption boxes, and it adds a normative annex for the 'coen' brand.

The amendment is organized around the updated scope wording, Clause 3.1.1, Clause 8.2, Clause 9, Clause 10, and Annex B.

Annex	What it covers
B	Normative rules for the 'coen' brand, including required file boxes and reader support for common encryption signaling

The document is still centered on common encryption signaling, not on defining every possible media-specific protection scheme. For non-NAL structured video tracks or items, the text points to derived specifications if subsample definitions are needed.

What are the key requirements of ISO/IEC 23001-7:2023/FDAmd 1?

ISO/IEC 23001-7:2023/FDAmd 1 extends the encryption model from AES-128 to AES-256 and tightens how boxes, flags and reader behavior are signaled. In practice, this is the part that file authors, packagers and reader developers need to implement correctly.

Encryption signaling in TrackEncryptionBox

Clause 8.2.1 defines several TrackEncryptionBox flags for subsample encryption, multiple-key use, SampleEncryptionBox, sample auxiliary information boxes, CENC Sample Encryption Information sample groups, and AVC slice-header encryption. Readers are told to treat encrypted files as erroneous when the box structure does not match the flag values. That matters because file validation depends on the box layout matching the chosen encryption signaling path.

Clause 8.2.2 updates the TrackEncryptionBox syntax, and Clause 8.2.3 adds use_AES_256. A value of 1 means a 256-bit key was used, while 0 means a 128-bit key was used. This gives readers a direct way to identify the AES key length used for encrypted samples.

AES modes and key sizes

Clause 9.3 extends AES-CTR to allow 128-bit or 256-bit keys, using FIPS-197 and NIST Special Publication 800-38A. Clause 9.4.3 extends AES-CBC in the same way for full-sample encryption. In practice, implementers can expect either key size, and tools can encrypt arbitrary-length byte streams without needing padding at the end of a sample.

Subsample and pattern encryption

Clause 9.4.1 allows full sample encryption or subsample encryption for all media types, while NAL structured video shall use subsample encryption. Clause 9.5.1 adds that subsample encryption may also be used for other media types, and Clause 9.5.3 says the specification does not define subsample structures for non-NAL structured video tracks or items. That means format-specific schemes must define those details before subsample encryption can be used there.

Clause 9.6 says pattern encryption applies when default_crypt_byte_block and default_skip_byte_block are non-zero in TrackEncryptionBox. For authors, that means the box values control whether pattern encryption is active.

Version rules and conformance

Clauses 10.1 to 10.4 update the allowed versions of TrackEncryptionBox and ItemEncryptionBox according to the encryption scheme in use. The practical point is that the box version and its fields must match the selected protection method, or the file signaling is not valid.

Common encryption brand 'coen'

Annex B is normative and defines the 'coen' brand for server-side dynamic adaptation. Files that list 'coen' in the compatible brands array of FileTypeBox shall follow the annex rules, and readers shall support the box sets listed there. This matters when a system needs a common way to signal encrypted media without tying the brand to one specific protection scheme such as 'cenc', 'cens', 'cbc1' or 'cbcs'.

What terms does ISO/IEC 23001-7:2023/FDAmd 1 define?

• Advanced Encryption Standard (AES) - The block cipher used here in 128-bit and 256-bit key sizes for sample encryption.
• AES-CTR - AES in Counter Mode, used to encrypt arbitrary-length byte streams without padding at the end of a sample.
• AES-CBC - AES in Cipher Block Chaining mode, used for full-sample encryption with 128-bit or 256-bit keys.
• TrackEncryptionBox - The 'tenc' box that carries default encryption parameters for a track.
• SampleEncryptionBox - The box that provides sample-level encryption information when that signaling path is used.
• CENC Sample Encryption Information ('seig') - A sample group used to describe multi-key encryption information.
• 'coen' - A compatible brand that constrains encryption-signaling boxes in files and readers.

Who uses ISO/IEC 23001-7:2023/FDAmd 1?

ISO/IEC 23001-7:2023/FDAmd 1 is used by media file format engineers, encoder and packager vendors, DRM and encryption system integrators, player and reader developers, and conformance or QA teams. They use it to choose AES-128 or AES-256 signaling, build or parse TrackEncryptionBox and related boxes, apply subsample or pattern encryption, and validate 'coen' brand files and readers. It is also relevant to server-side dynamic adaptation systems that need a common way to signal protected media.

What changed in ISO/IEC 23001-7:2023/FDAmd 1 from the previous edition?

This amendment adds AES-256 support to Part 7, expands the AES-CTR and AES-CBC wording to cover 256-bit keys, introduces use_AES_256 in TrackEncryptionBox, clarifies subsample and pattern encryption behavior, and adds Annex B on the 'coen' brand and reader support. It also revises the TrackEncryptionBox flag definitions and version/signaling rules used for encrypted tracks and items.

Which standards are used with ISO/IEC 23001-7:2023/FDAmd 1?

• FIPS-197 - Specifies the Advanced Encryption Standard used for AES-CTR and AES-CBC.
• NIST Special Publication 800-38A - Provides the block cipher mode guidance used for Counter Mode and Cipher Block Chaining mode.

What does the ISO/IEC 23001-7:2023/FDAmd 1 document contain?

ISO/IEC 23001-7:2023/FDAmd 1 contains revised normative text, a TrackEncryptionBox syntax update, and new semantics for the use_AES_256 field. It also includes detailed flag behavior for encryption signaling, mode text for AES-CTR and AES-CBC, and revised version rules for track and item encryption boxes. Annex B provides tables for required boxes and supported boxes under the 'coen' brand. The amendment is written as an update to existing clauses rather than as a separate tutorial or implementation guide.

FINAL DRAFT
Amendment
ISO/IEC
23001-7:2023/
FDAM 1
ISO/IEC JTC 1/SC 29
Information technology — MPEG
Secretariat: JISC
systems technologies —
Voting begins on:
2026-08-25
Part 7:
Common encryption in ISO base
Voting terminates on:
2026-10-20
media file format files
AMENDMENT 1: Support for AES-256
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
ISO/IEC 23001­7:2023/FDAM 1:2026(en) © ISO/IEC 2026

FINAL DRAFT
ISO/IEC 23001-7:2023/FDAM 1:2026(en)
Amendment
ISO/IEC
23001-7:2023/
FDAM 1
ISO/IEC JTC 1/SC 29
Information technology — MPEG
Secretariat: JISC
systems technologies —
Voting begins on:
Part 7:
Common encryption in ISO base
Voting terminates on:
media file format files
AMENDMENT 1: Support for AES-256
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO/IEC 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/IEC 23001­7:2023/FDAM 1:2026(en) © ISO/IEC 2026

© ISO/IEC 2026 – All rights reserved
ii
ISO/IEC 23001-7:2023/FDAM 1:2026(en)
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.
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 or www.iec.ch/members_experts/refdocs).
ISO and IEC draw attention to the possibility that the implementation of this document may involve the
use of (a) patent(s). ISO and IEC take no position concerning the evidence, validity or applicability of any
claimed patent rights in respect thereof. As of the date of publication of this document, ISO and IEC had not
received notice of (a) patent(s) which may be required to implement this document. However, implementers
are cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents and https://patents.iec.ch. ISO and IEC shall not be held
responsible for identifying any or all such patent rights.
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.
In the IEC, see www.iec.ch/understanding-standards.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 29, Coding of audio, picture, multimedia and hypermedia information.
A list of all parts in the ISO/IEC 23001 series can be found on the ISO and IEC websites.
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 and
www.iec.ch/national-committees.

© ISO/IEC 2026 – All rights reserved
iii
ISO/IEC 23001-7:2023/FDAM 1:2026(en)
Information technology — MPEG systems technologies —
Part 7:
Common encryption in ISO base media file format files
AMENDMENT 1: Support for AES-256

Scope
Replace
" The AES-128 symmetric block cipher is incorporated by reference to encrypt elementary stream data
contained in media samples. Both AES counter mode (CTR) and Cipher Block Chaining (CBC) are specified in
separate protection schemes."
with
" The AES-128 or AES-256 symmetric block cipher is incorporated by reference to encrypt elementary
stream data contained in media samples. Both AES counter mode (CTR) and Cipher Block Chaining (CBC) are
specified in separate protection schemes.”

3.1.1
Replace
"16-byte extent of sample data that may be encrypted or decrypted by the AES-128 block cipher, in which
case, a cipher block"
with
"16-byte extent of sample data that may be encrypted or decrypted by the AES-128 or AES-256 block cipher,
in which case, a cipher block"

8.2.1
Add the following text at the end of the subclause:
The following 2-bits normative flags are defined for TrackEncryptionBox. The default value for the flags
field is 0. Readers shall consider as erroneous encrypted files with a box structure that is inconsistent with
the values indicated in these 2-bits flags.
use_subsample_encryption: flag mask is 0x000003.
When (flags & 0x000003) is equal to 0, it indicates that for any sample associated with this TrackEncryptionBox
box, the presence or absence of BytesOfClearData and BytesOfProtectedData is undefined.
When (flags & 0x000003) is equal to 1, it indicates that for any sample associated with this
TrackEncryptionBox box, BytesOfClearData and BytesOfProtectedData shall be present in the structure
describing the encryption parameters, i.e., either using the SampleEncryptionBox box or the sample auxiliary
information boxes (‘saiz’ and ‘saio’ boxes).

© ISO/IEC 2026 – All rights reserved
ISO/IEC 23001-7:2023/FDAM 1:2026(en)
When (flags & 0x000003) is equal to 2, BytesOfClearData and BytesOfProtectedData shall not be present,
The value 0x000003 shall not be used.
Default value is 0.
use_multi_key: flag mask is 0x00000C.
When ((flags & 0x00000C) >> 2) is equal to 0, it indicates that for samples associated with this
TrackEncryptionBox box, the use of multiple keys is undefined,
When ((flags & 0x00000C) >> 2) is equal to 1, it indicates that for samples associated with this
TrackEncryptionBox box, there are multiple keys in use. If the CENC Sample Encryption Information
(‘seig’) sample group is used, there shall be at least one CENC Sample Encryption Information sample
group description entry with multi_key_flag set to 1.
When ((flags & 0x00000C) >> 2) is equal to 2, it indicates that there is a single key in use per sample
associated with this TrackEncryptionBox box. If the CENC Sample Encryption Information sample group is
used, the multi_key_flag in all CENC Sample Encryption Information sample group description entries shall
be set to 0.
The value 0x00000C shall not be used.
Default value is 0.
use_senc: flag mask is 0x000030.
When ((flags & 0x000030) >> 4) is equal to 0, the presence or absence of the SampleEncryptionBox box is
undefined.
When ((flags & 0x000030) >> 4) is equal to 1, it indicates, that the SampleEncryptionBox box is used to
provide sample encryption information for samples associated with this TrackEncryptionBox box.
When ((flags & 0x000030) >> 4) is equal to 2, there shall be no SampleEncryptionBox box associated with
samples associated with this TrackEncryptionBox box.
The value 0x000030 shall not be used.
Default value is 0.
use_sai: flag mask is 0x0000C0.
When ((flags & 0x0000C0) >> 6) is equal to 0, it indicates that the presence or absence of the sample auxiliary
information (‘saiz’ and ‘saio’) boxes is undefined.
When ((flags & 0x0000C0) >> 6) is equal to 1, it indicates that the sample auxiliary information (‘saiz’
and ‘saio’) boxes are used to provide sample encryption information for samples associated with this
TrackEncryptionBox box.
When ((flags & 0x0000C0) >> 6) is equal to 2, there shall be no sample auxiliary information (‘saiz’ and
‘saio’) boxes associated for samples associated with this TrackEncryptionBox box.
The value 0x0000C0 shall not be used.
Default value is 0.
© ISO/IEC 2026 – All rights reserved
ISO/IEC 23001-7:2023/FDAM 1:2026(en)
use_seig: flag mask is 0x000300.
When ((flags & 0x000300) >> 8) is equal to 0, it indicates that the presence or abse
...

ISO/IEC JTC 1/SC 29 N 25617
Date: 2025-11-06
ISO/IEC 23001-7:2023/DAMFDAmd 1
ISO/IEC JTC 1:2025(en)/SC 29
ISO/IEC JTC 1/SC 29/WG 3
Secretariat: JISC
Date: 2026-08-11
Information technology — MPEG systems technologies— —
Part 7:
Common encryption in ISO base media file format files —
Amendment
AMENDMENT 1: Support for AES-256
Élément introductif — Élément central — Partie 5: Élément complémentaire

Copyright notice
This ISO document is a
working draftFDIS stage
ISO/IEC 23001-7:2023/DAMFDAmd 1:2025(en)
© ISO/IEC 2026
All rights reserved. Unless otherwise specified, or committee draft and is copyright-protected by ISO. While required
in the reproductioncontext of working drafts or committee drafts in any form for use by participants in the ISO
standards development process is permitted without prior permission from ISO, neither its implementation, no part
of this document nor any extract from itpublication may be reproduced, stored or utilized otherwise in any form or
transmitted in any form for any other purposeby any means, electronic or mechanical, including photocopying, or
posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO.
Requests for permission to reproduce this document for at the purpose of selling it should be addressed as shownaddress
below or to ISO'sISO’s member body in the country of the requester:.
[Indicate the full address, telephone number, fax number, telex number, and electronic mail address, as appropriate,
of the Copyright Manager of the ISO member body responsible for the secretariat of the TC or SC within the framework
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Reproduction for sales purposes may be subject to royalty payments or a licensing agreement.
Violators may be prosecuted.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
E-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
© ISO/IEC 2025 2026 – 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.
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/directiveswww.iso.org/directives or
www.iec.ch/members_experts/refdocswww.iec.ch/members_experts/refdocs).
ISO and IEC draw attention to the possibility that the implementation of this document may involve the use of
(a) patent(s). ISO and IEC take no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO and IEC had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent database
available at www.iso.org/patents and https://patents.iec.ch.www.iso.org/patents and https://patents.iec.ch.
ISO and IEC shall not be held responsible for identifying any or all such patent rights.
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.www.iso.org/iso/foreword.html. In the IEC, see www.iec.ch/understanding-
standardswww.iec.ch/understanding-standards.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 29, Coding of audio, picture, multimedia and hypermedia information.
A list of all parts in the ISO/IEC 23001 series can be found on the ISO and IEC websites.
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 and www.iec.ch/national-
committees.www.iso.org/members.html and www.iec.ch/national-committees.
© ISO/IEC 2026 – All rights reserved
iv
ISO/IEC 23001-7:2023/DAM 1:2025(en)
Information technology — MPEG systems technologies— —
Part 7:
Common encryption in ISO base media file format files — Amendment
AMENDMENT 1: Support for AES-256

Scope
Replace
" The AES-128 symmetric block cipher is incorporated by reference to encrypt elementary stream data
contained in media samples. Both AES counter mode (CTR) and Cipher Block Chaining (CBC) are specified in
separate protection schemes."
with
" The AES-128 or AES-256 symmetric block cipher is incorporated by reference to encrypt elementary stream
data contained in media samples. Both AES counter mode (CTR) and Cipher Block Chaining (CBC) are specified
in separate protection schemes.”

3.1.1
Replace
"16-byte extent of sample data that may be encrypted or decrypted by the AES-128 block cipher, in which
case, a cipher block. "
with
"16-byte extent of sample data that may be encrypted or decrypted by the AES-128 or AES-256 block cipher,
in which case, a cipher block."

8.2.1
Add the following text at the end of the subclause:
The following 2-bits normative flags are defined for TrackEncryptionBox. The default value for the
flags field is 0. Readers shall consider as erroneous encrypted files with a box structure that is inconsistent
with the values indicated in these 2-bits flags.
use_subsample_encryption: flag mask is 0x000003.
© ISO/IEC 2025 – All rights reserved
When (flags & 0x000003) is equal to 0, it indicates that for any sample associated with this
TrackEncryptionBox box, the presence or absence of BytesOfClearData and
BytesOfProtectedData is undefined.
When (flags & 0x000003) is equal to 1, it indicates that for any sample associated with this
TrackEncryptionBox box, BytesOfClearData and BytesOfProtectedData shall be present in
the structure describing the encryption parameters, i.e., either using the SampleEncryptionBox box or
the sample auxiliary information boxes (‘saiz’ and ‘saio’ boxes).
When (flags & 0x000003) is equal to 2, BytesOfClearData and BytesOfProtectedData shall not be
present,
The value 0x000003 shall not be used.
Default value is 0.
use_multi_key: flag mask is 0x00000C.
When ((flags & 0x00000C) >> 2) is equal to 0, it indicates that for samples associated with this
TrackEncryptionBox box, the use of multiple keys is undefined,
When ((flags & 0x00000C) >> 2) is equal to 1, it indicates that for samples associated with this
TrackEncryptionBox box, there are multiple keys in use. If the CENC Sample Encryption Information
(‘seig’) sample group is used, there shall be at least one CENC Sample Encryption Information sample
group description entry with multi_key_flag set to 1.
When ((flags & 0x00000C) >> 2) is equal to 2, it indicates that there is a single key in use per sample associated
with this TrackEncryptionBox box. If the CENC Sample Encryption Information sample group is used,
the multi_key_flag in all CENC Sample Encryption Information sample group description entries shall be
set to 0.
The value 0x00000C shall not be used.
Default value is 0.
use_senc: flag mask is 0x000030.
When ((flags & 0x000030) >> 4) is equal to 0, the presence or absence of the SampleEncryptionBox box
is undefined.
When ((flags & 0x000030) >> 4) is equal to 1, it indicates, that the SampleEncryptionBox box is used to
provide sample encryption information for samples associated with this TrackEncryptionBox box.
When ((flags & 0x000030) >> 4) is equal to 2, there shall be no SampleEncryptionBox box associated
with samples associated with this TrackEncryptionBox box.
The value 0x000030 shall not be used.
Default value is 0.
© ISO/IEC 2026 – All rights reserved
ISO/IEC 23001-7:2023/DAMFDAmd 1:2025(en)

use_sai: flag mask is 0x0000C0.
When ((flags & 0x0000C0) >> 6) is equal to 0, it indicates that the presence or absence of the sample auxiliary
information (‘saiz’ and ‘saio’) boxes is undefined.
When ((flags & 0x0000C0) >> 6) is equal to 1, it indicates that the sample auxiliary information (‘saiz’ and
‘saio’) boxes are used to provide sample encryption information for samples associated with this
TrackEncryptionBox box.
When ((flags & 0x0000C0) >> 6) is equal to 2, there shall be no sample auxiliary information (‘saiz’ and
‘saio’) boxes associated for samples associated with this TrackEncryptionBox box.
The value 0x0000C0 shall not be used.
Default value is 0.
use_seig: flag mask is 0x000300.
When ((flags & 0x000300) >> 8) is equal to 0, it indicates that the presence or absence of a CENC Sample
Encryption Information sample group is undefined.
When ((flags & 0x000300) >> 8) is equal to 1, it indicates that some samples associated with this
TrackEncryptionBox box are associated with a CENC Sample Encryption Information sample group.
When ((flags & 0x000300) >> 8) is equal to 2, there shall be no CENC Sample Encryption Information sample
group box associated with the samples associated with this TrackEncryptionBox box.
The value 0x0000300 shall not be used.
Default value is 0.
use_avc1_ctr_encrypted_slice_header: flag mask is 0x000C00.
When ((flags & 0x000C00) >> 10) is equal to 0, no information is provided about whether the slice headers
are encrypted or not.
When ((flags & 0x000C00) >> 10) is equal to 1, it indicates that all VCL NAL units are encrypted, including the
slice header. This shall be set only for AVC video using ‘avc1’ sample description stream format in AES-CTR
mode (for compatibility with the first edition of this part of ISO/IEC 23001, see also 9.5.2.2).
When ((flags & 0x000C00) >> 10) is equal to 2, the slice headers in the VCL NAL units are unencrypted.
The value 0x0000C00 shall not be used.
Default value is 0.
NOTE: For fragmented files, readers may not know at the beginning of the file if SampleEncryptionBox, sample
auxiliary information (‘saiz’ and ‘saio’) boxes or CENC Sample Encryption Information sample group is used.

© ISO/IEC 2025 2026 – All rights reserved
8.2.2
Replace the subclause with :the following::
8.2.2.  Syntax
aligned(8) class TrackEncryptionBox extends FullBox('tenc', version, flags)
{
{
unsigned int(8)   rese
...