ISO/IEC 23001-17:2024/Amd 1:2025

International
Standard
ISO/IEC 23001-17
First edition
Information technology — MPEG
2024-02
systems technologies —
AMENDMENT 1
Part 17:
2025-07
Carriage of uncompressed video and
images in ISO base media file format
AMENDMENT 1: High precision
timing tagging
Technologies de l'information — Technologies des systèmes MPEG —
Partie 17: Transport de vidéos et d'images non compressées dans
le format ISO de base pour les fichiers médias
AMENDEMENT 1: Marquage temporel de haute précision
Reference number
ISO/IEC 23001-17:2024/Amd. 1:2025(en) © ISO/IEC 2025

ISO/IEC 23001-17:2024/Amd. 1:2025(en)
© ISO/IEC 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by 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 at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
© ISO/IEC 2025 – All rights reserved
ii
ISO/IEC 23001-17:2024/Amd. 1:2025(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 23090 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 2025 – All rights reserved
iii
ISO/IEC 23001-17:2024/Amd. 1:2025(en)
Information technology — MPEG systems technologies —
Part 17:
Carriage of uncompressed video and images in ISO base
media file format
AMENDMENT 1: High precision timing tagging

Terms and definitions
Add the following terms and definitions:
3.12
TAI
international atomic time
high-precision continuous scale of time derived from hundreds of precise atomic clocks from around the
world and maintained as closely as possible to the International System (SI) second.
Note 1 to entry: Current practice achieves a maximum deviation of approximately one second every 100 million years.
Note 2 to entry: The abbreviated term comes from the French "Temps Atomique International".
3.13
TAI clock
clock capable of synchronizing to a source of TAI time and generating TAI timestamps
3.14
receptor clock
clock located where measurements are made (e.g. local to a sensor) and capable of synchronizing to a source
of time from a remote clock.
3.15
remote clock
clock capable of transmitting time over significant distances and usually highly accurate (e.g. GPS or PTP
primary reference clock)
3.16
coordinated universal time
UTC
international standard for regulating clocks and time, forming a basis for civil time
Note 1 to entry: UTC is based on TAI but includes irregularly inserted leap second additions or subtractions to account
for variation in the earth’s rotation.
3.17
global positioning system
GPS
satellite system providing global positioning, navigation, and timing services
Note 1 to entry: Timing services are based on TAI time.

© ISO/IEC 2025 – All rights reserved
ISO/IEC 23001-17:2024/Amd. 1:2025(en)
3.18
precision time protocol
PTP
protocol for synchronizing clocks to a source of TAI time across computer networks
Note 1 to entry: IEEE 1588-2008 defines the precision time protocol.
Note 2 to entry: PTP systems can achieve measurement uncertainties below a microsecond.
3.19
network time protocol
NTP
protocol for synchronizing clocks to UTC time across computer networks
Note 1 to entry: RFC 5905 defines the Network Time Protocol.
Note 2 to entry: Systems using NTP typically achieve measurement uncertainties in the range of milliseconds.
3.20
SI second
International System of Units (SI) base unit for measuring time

6.1.4.2
Replace the text with the following:

aligned(8) class ComponentReferenceLevelBox extends FullBox('clev', 0, 0) {
unsigned int(32) level_count;
{
unsigned int(32) component_index;
unsigned int(1) clip_range;
bits(7) reserved = 0;
signed int(32) black_level;
signed int(32) white_level;
} [level_count];
}
6.1.4.3
Replace the text with the following:
level_count indicates the number of components for which levels are described
th
component_index indicates the index of the N component listed in the associated ComponentDefinitionBox.
th
clip_range indicates if the levels indicate a clip range or an affine transformation of the N component values
th
black_level indicates the black level for the N component. This value shall be coded using the two’s-
complement representation.
th
white_level indicates the white level for the N component; this value shall be greater than the black_
level value and shall be coded using the two’s-complement representation.

Clause 8
Add the following new clause, after Clause 7 and before the bibliography:
8  Labeling of Samples and Items
8.1  High Precision Time Tagging

© ISO/IEC 2025 – All rights reserved
ISO/IEC 23001-17:2024/Amd. 1:2025(en)
To support applications requiring high resolution and high accuracy time labeling of media items and track
samples, this clause provides a labeling method based on International Atomic Time (TAI). A TAI timestamp
is a measurement of a TAI clock represented as a discrete integer number of nanoseconds since the TAI epoch
of 1958-01-01T00:00:00.0. Additionally, this clause defines TAI timestamp quality status metadata included
with each timestamp. Ideally, to be useful and support a broad range of use cases, an ideal timestamp
labeling utility benefits from the following attributes:
a) Total ordering: timestamps provide total ordering in which events occur.
b) Relative differencing: timestamps support the ability to compute the difference in time between two
events, in SI seconds.
c) Absolute time: timestamps are in a known, universal absolute time reference, enabling correlation of
information from sensors and events in different locations.
TAI timestamps are measurements from a TAI clock. TAI clocks report timestamp values relative to the TAI
epoch. They provide the ability to search and discover media content based on universal, real-world time. In
situations where an adjustment or correction to a timestamp is necessary to improve the accuracy, such as
when synchronization to a remote clock is not available during data collection, the ability to modify values
using adjustment information post collection is provided, along with a flag to indicate the inclusion of the
adjustment.
TAI clocks are “receptor clocks”, typically receiving synchronization data with one or more remote clocks
(e.g. GPS and PTP primary reference clocks) which are sources of TAI time. Different types of receptor
clocks have different levels of quality when synchronizing with remote clocks; therefore, this clause defines
metadata for describing the TAI clock, its capabilities, and its state when sampling a timestamp.
Each TAI timestamp is associated with the beginning of a physical measurement, such as the start of
exposure for an imaging sensor. For sensors with variable timing, such as rolling shutters, the TAI timestamp
is associated with the first pixel(s) initiating an exposure for a frame. The timing associated with remaining
pixel exposures is dependent on the sensor architecture and is outside the scope of the metadata described
in this subclause. When extracting data from an image or sample, such as the location of an object in an
image, the location data inherits its time from the image frame.
The creation and recording of synthetic data, such as a simulation, is not a measurement of the physical
world. The implementation of time labeling, including alignment of synthetic data to real-world data is
application dependent and depends on use case needs. In these cases, labeling of the media as synthetic is
outside the scope of metadata described in this subclause.
For media captured in real-time, valid TAI timestamps for the media monotonically increase; however, there
are situations where the monotonic nature does not always hold, such as when losing remote to receptor
clock synchronization and a resulting discontinuity upon resync occurs. Synchronization status metadata is
available to indicate when a receptor clock is not in a synchronous state with the remote clock.
TAI is different from Coordinated Universal Time (UTC) because UTC includes irregularly inserted
discontinuities called leap seconds. When converting TAI time to UTC, applications convert the TAI
timestamp to date text form and subtract the correct leap seconds value for the date text:
UTC date-text = TAI date-text - leap seconds (based on value at time of measurement)
When converting from timestamps derived from UTC, such as Network Time Protocol (NTP), reverse the
computation. To perform a conversion from UTC time to a TAI timestamp, transform the UTC time to a UTC
nanosecond timestamp relative to the TAI epoch, then adjust for leap seconds:
TAI timestamp = UTC timestamp + leap seconds (based on value at time of measurement)
A caveat of using UTC-based systems for capturing timestamps is the leap-second adjustment methods
employed by various implementations. In practice these methods include stopping the remote clock, slewing
the clock at a slow rate, etc. which may introduce errors and compromise the ability to generate accurate
time differences on occasions when leap seconds occur. For these reasons, this standard recommends
sourcing time from a clock which does not adjust for leap seconds, i.e., TAI based clocks.

© ISO/IEC 2025 – All rights reserved
ISO/IEC 23001-17:2024/Amd. 1:2025(en)
Table 6 provides equations to convert times from common time sources (i.e., GPS, PTP, and NTP) to TAI
time. The first column of Table 6 is the name of the time source; the second column is the epoch of the time
source and whether the epoch is defined in the TAI or UTC time system (for informational use only); the
third column provides the equation to convert the time from the time source’s epoch offset to TAI’s epoch
offset. The first step, before applying the equations in the table, is to convert the source time to nanoseconds.
The GPS and PTP time standards measure time without using leap seconds, therefore their conversions
are straight forward offset additions (based on their respective epoch). Vendors may implement receptor
clocks with an epoch other than the base standard; as a result, writers must account for use of the vendor’s
implemented epoch when performing conversions between time systems.
[4]
The NTP standard measures time in UTC, with leap second offsets, so the NTP equation removes leap
seconds, where the leap second value comes from a leap second table lookup. The GPS epoch is based on
a specific UTC time, but GPS time does not implement leap seconds and tracks with TAI. The POSIX Time
standard uses an epoch of Jan 1, 1970 (UTC), which is offset from Jan 1, 1970 (TAI) by 8.000082 seconds.
The 82 microseconds are due to non-integer leap second computations used before 1972. As a result, the
c
...