ISO IEC 23000-19:2018 download free.Information technology — Multimedia application format (MPEG.A) — Part 19: Common media application format (CMAF) for segmented media.
Introduction
Common Media Application Format (CMAF) combines and constrains several MPEG specifications to define a multimedia format that is optimized for delivery cia single adaptive multimedia presentation to a variety of devices, using a variety oladaptive streaming, broadcast, download, and storage methods.
Several MPEG specifications have been adopted for much of the video delivered over the Internet and other IP networks (cellular, cable, broadcast, etc.). Various organizations have taken MPEG’s core coding, file format and system standards and combined them into their own specifications for their specific application. While these specifications are similar, their differences result in unnecessary duplication of engineering effort and duplication of identical content in slightly different formats, which results in increased storage and delivery costs.
CMAF provides a common media specification that application specifications, such as MPEG Dynamic Adaptive Streaming over HTTP (DASH), can reference and a common media format that allows a single encoded multimedia presentation to be used by many applications.
1 Scope
ISO IEC 23000-19 specifies the CMAF multimedia format, which contains segmented media objects optimized for streaming delivery and decoding on end user devices in adaptive multimedia presentations.
CMAF specifies a track format derived from the ISO Base Media File Format, then derives addressable media objects from CMAF tracks that can be used for storage and delivery.
CMAF specifies sets of tracks that share encoding and packaging constraints that enable the selection of multiple tracks to form a multimedia presentation and allow seamless switching of alternative encodings of the same content at different bit rates, frame rates, resolution, etc.
CMAF specifies a hypothetical application model that determines how tracks in a CMAF presentation are intended to be combined and synchronized to form a multimedia presentation. The model abstracts delivery to allow any delivery method. The hypothetical application model assumes a manifest and player, but CMAF does not specify a manifest, player, or delivery protocol, with the intent that any that support the hypothetical application model can be used.
CMAF specifies media profiles and brands that constrain media encoding and packaging of CMAF tracks to enable seamless adaptive switching of tracks and allow devices to identify compatible content by its brand.
CMAF specifies presentation profiles that conditionally require sets of CMAF tracks conforming to specified media profiles and allow content creators and devices to Identify compatible multimedia presentations.
CMAF enables extensibility by specifying how new media profiles and presentation profiles can be specified and identified and includes guidelines for those specifications.
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.
lSO/IEC 14496-1, Information technology — Coding of audio-vLcuol objects — Part 1: Systems ISO/IEC 14496-3. Information technology — Coding of audio-visual objects — Part 3: Audio
ISO/IEC 14496-10, Information technology — Coding of audio-visual objects — Part 10: Advanced Video Coding
ISO/IEC 1449642, Information technology — Coding of audio-visual objects — Part 12: iso base media ide form at
ISO/IF.C 14496-14. Information technology — Coding of audio-visual objects — Part 14: MP4fileformat
recommends how to specify additional CMAF media profiles and presentation profiles. whkh can be specified by other documents and organizations.
CMAF presentation profiles and CMAF media profiles are specified in annexes to allow the addition of new profiles without changing the core document. Mditional informative annexes have been added to provide explanations and recommendations on specific topics.
The following is a list of the main clauses of this document, with a brief description of each.
Clausefl describes the segmented media encoding and playback model using the media objects defined by the CMAF.
Clause 7 describes the use of ISO Base Media File Format for the Common Media Application Format brand.
cuse_8 describes how digital rights management information and encryption is applied to the Common Media Application Format.
Clause.9 describes the general video track format, constraints for NAL structured video tracks, and the AVC video track format.
Clause 10 describes the general audio track format and specifies two AAC audio CMAF media profiles.
Clausefl describes the subtitle track format, CMAF media profiles for WebVTT and IMSCI TTML subtitles, and signalling of CTA &OH/708 captions embedded in video streams.
Clause 12 descrIbes the general requirements for CMAF media profiles and CMAF presentation profiles. Annex A describes several C4AF media profiles, their compatibility brands, and a CMAF presentation profile that conditionaLly requires some of those media profiles.
Annex U describes packaging and codec constraints for some CMAF media profiles using the HEVC video codec.
Annex C describes framing and encoding CMAF switching sets using subsampling and scaling of video to provide seamless playback with adaptive bit rate and scaling.
Annex D describes examples of player track selection, synchronization, and adaptive switching of a CMAF presentation.
Annex E describes the use of event messages attached to media objects to deliver metadata.
Annex F describes maintaining presentation timing and delivery In the event of missing media samples
and resources.
Annex G describes encoding recommendations for AAC audio CMAF tracks conforming to adaptive
CMAF switching sets.
6 CMAF hypothetical application model, media object model, and profiles
6.1 OvervIew of the hypothetical application model and media object model
CMAF defines a hypothetical application model so that encoding to that model results in consistent CMAF track encoding. representation in manifests, track selection, late binding, synchronization, decoding, and rendering of CMAF presentations.
Decoding requirenients can be inferred from encoding constraints and the hypothetical application model, but are not directly specified by CMAF. CMAF does not specify manifest formats or associated resource identification and transport. However, CMAF does specify CMAF addressable media objects derived from encoded CMAF fragments, which can be referenced as resources by a manliest. External specifications can define how a manifest describes a CMAF presentation, including identfying CMAF
This clause specifies general constraints on all video CMAF tracks and video CMAF switching sets, then derives more specific constraints for NAL structured video from that. Then, AVC CMAF track format is derived from NA(. structured video CMAF tracks.
Video media profiles can be derived from the general video track format. NAL structured video track format, or AVC video track format, as appropriate.
This clause specifies:
— general constraints on a video CMAF track. in addition to conforming to the ‘cmfc’ brand;
— general constraints on multiple CMAF tracks conforming to a CMAF switching set intended to enable seamless adaptive switching of video;
— NAL structured video constraints for CMAF switching sets;
— single initialization constraints for NAt. structured video CMAF switching sets;
— constraints between aligned CMAF switching sets containing NAt. structured video;
— AVC video CMAF track constraints, used to derive the AVC video CMAF media profiles defined in Al.
The CMAF track format for NAt. structured video is derived from lSO/IF.C 14496-15 and requires boxes defined in that specification.
Some CMAF video media profiles using the AVC codec are specified in Annex A. They define widely used video Formats, such as SD, HD, and UHD, by specifying codec parameters, such as the maximum codec profile and level that can be encoded, and video parameters such as maximum resolution, frame rate, bit depth, transfer function, colour space, colour subsampling. etc.
Video CMAF tracks that carry a compatibility brand indicating parameter limits that also conform to a higher CMAF media profile (i.e. a lower codec profile and level) are considered to also conform to that higher CMAF media profile. For example, a CMAF track with an SD (standard definition) AVC compatibility brand also conforms to a CMAF HD (high definition) AVC media profile. In general, a media profile is considered contained In another media profile If It can always be decoded and rendered by all decoders conforming to the containing media profile.
Other CMAF media profiles for video codecs may be defined in other specifications, as long as they conform to CMAF track constraints specilied in Clauses 7 and and recommendations in Clause 12. Video media profiles may optionally specify CMAF track constraints for CMAF switching sets to enable seamless adaptive switching and may optionally specify single initialization CMAF switching set constraints,
For additional Information, see Clause.l2 and Annez..A.
9.2 General video CMAF track format
9.2.1 General video CMAF track structure and constraints
Video CMAF tracks shall conform to the cmfc’ compatibility brand as specified in Clauses.2 and 8 and general CMAF video track constraints specified in 92.
9.22 Video Media Header(’vmhd’)
VideoMedloHeaderBoxes in a video CMAF track shall conform to ISO/IEC 1449642 with the following additional constraints.
— The following fields shall be set to their default values as defined In lSO/IEC 14496-12:
— veraion—O.