2 Rec. ITU-T H.265 v5 (02/2018)
0.5 Publication and versions of this Specification
This Specification has been jointly developed by ITU-T Video Coding Experts Group (VCEG) and the ISO/IEC Moving
Picture Experts Group (MPEG). It is published as technically-aligned twin text in both ITU-T and ISO/IEC. As the basis
text has been drafted to become both an ITU-T Recommendation and an ISO/IEC International Standard, the term
"Specification" (with capitalization to indicate that it refers to the whole of the text) is used herein when the text refers to
itself.
This is the fourth version of this Specification.
Rec. ITU-T H.265 | ISO/IEC 23008-2 version 1 refers to the first approved version of this Recommendation | International
Standard. The first edition published by ITU-T as Rec. ITU-T H.265 (04/2013) and by ISO/IEC as ISO/IEC 23008-2:2013
corresponded to the first version.
Rec. ITU-T H.265 | ISO/IEC 23008-2 version 2 refers to the integrated text additionally containing format range
extensions, scalability extensions, multiview extensions, additional supplement enhancement information, and corrections
to various minor defects in the prior content of the Specification. The second edition published by ITU-T as Rec. H.265
(10/2014) and by ISO/IEC as ISO/IEC 23008-2:2015 corresponded to the second version.
Rec. ITU-T H.265 | ISO/IEC 23008-2 version 3 refers to the integrated text additionally containing 3D extensions,
additional supplement enhancement information, and corrections to various minor defects in the prior content of the
Specification. The third edition published by ITU-T as Rec. H.265 (04/2015) corresponded to the third version.
Rec. ITU-T H.265 | ISO/IEC 23008-2 version 4 refers to the integrated text additionally containing screen content coding
extensions profiles, scalable range extensions profiles, additional high throughput profiles, additional supplement
enhancement information, additional colour representation identifiers, and corrections to various minor defects in the prior
content of the Specification. The fourth edition published by ITU-T as Rec. H.265 (12/2016) and by ISO/IEC as ISO/IEC
23008-2:2017 corresponded to the fourth version.
Rec. ITU-T H.265 | ISO/IEC 23008-2 version 5 (the current version) refers to the integrated text additionally containing
additional SEI messages that include omnidirectional video SEI messages, a Monochrome 10 profile, a Main 10 Still
Picture profile, and corrections to various minor defects in the prior content of the Specification.
0.6 Profiles, tiers and levels
This Recommendation | International Standard is designed to be generic in the sense that it serves a wide range of
applications, bit rates, resolutions, qualities and services. Applications should cover, among other things, digital storage
media, television broadcasting and real-time communications. In the course of creating this Specification, various
requirements from typical applications have been considered, necessary algorithmic elements have been developed, and
these have been integrated into a single syntax. Hence, this Specification will facilitate video data interchange among
different applications.
Considering the practicality of implementing the full syntax of this Specification, however, a limited number of subsets of
the syntax are also stipulated by means of "profiles", "tiers" and "levels". These and other related terms are formally defined
in clause 3.
A "profile" is a subset of the entire bitstream syntax that is specified in this Recommendation | International Standard.
Within the bounds imposed by the syntax of a given profile, it is still possible to require a very large variation in the
performance of encoders and decoders depending upon the values taken by syntax elements in the bitstream such as the
specified size of the decoded pictures. In many applications, it is currently neither practical nor economical to implement
a decoder capable of dealing with all hypothetical uses of the syntax within a particular profile.
In order to deal with this problem, "tiers" and "levels" are specified within each profile. A level of a tier is a specified set
of constraints imposed on values of the syntax elements in the bitstream. These constraints may be simple limits on values.
Alternatively they may take the form of constraints on arithmetic combinations of values (e.g., picture width multiplied by
picture height multiplied by number of pictures decoded per second). A level specified for a lower tier is more constrained
than a level specified for a higher tier.
Coded video content conforming to this Recommendation | International Standard uses a common syntax. In order to
achieve a subset of the complete syntax, flags, parameters and other syntax elements are included in the bitstream that
signal the presence or absence of syntactic elements that occur later in the bitstream.
0.7 Overview of the design characteristics
The coded representation specified in the syntax is designed to enable a high compression capability for a desired image
or video quality. The algorithm is typically not lossless, as the exact source sample values are typically not preserved
through the encoding and decoding processes. A number of techniques may be used to achieve highly efficient
compression. Encoding algorithms (not specified in this Recommendation | International Standard) may select between