ISO IEC 23000-19:2018 pdf download.Information technology - Multimedia application format (MPEG-A)
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 requirements 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 manifest. External specifications can define how a manifest describes a CMAF presentation, including identifying CMAF addressable media objects as resources and representing their logical relationships determined by the CMAF tracks, CMAF switching sets, CMAF selection sets, and CMAF presentations they are derived from.
Figure 1 ilustrates the media objects that are specified by CMAF, starting with the encoded CMAF fragments that form CMAF tracks, then logical CMAF track sets determined by CMAF track encoding constraints, then derived CMAF addressable media objects that can package encoded CMAF fragments or their media samples for storage and delivery.
Figure 1 ilustrates the mapping between CMAF specified CMAF presentations, and externally specified manifests and resources. Multiple manifests may reference the same CMAF presentation and CMAF addressable media objects. Specification of manifests and resource delivery is outside the scope of this document.
To accurately represent a CMAF presentation, a manifest will describe CMAF track relationships determined by each track's source content and CMAF track encoding constraints, e.g. that CMAF tracks belong to the same CMAF switching set, which belongs to a CMAF selection set. CMAF groups CMAF tracks based on their encoding constraints in logical media objects called CMAF selection sets and CMAF switching sets that also determine intended use in late binding, track selection, seamless switching,and synchronization. Additional CMAF track metadata such as CMAF media profile brands, "codecs" parameters, language fields, etc. can be included in manifests to enable adaptive track selection and playback, optimized for each user and device.
Manifests can reference CMAF addressable media objects by resource identifiers used by manifests and servers to select the identified CMAF addressable media objects for delivery and playback.Multiple CMAF addressable media object types are specified for different delivery use cases. Use cases include prerecorded content that is downloaded or streamed as files, and live and on demand adaptive streaming over the Internet. The size of the CMAF addressable media objects can be optimized for efficient download and CDN caching, or fast bit rate switching and low latency, depending on the application.
Eigure 2 ilustrates the relationship between CMAF and streaming specifications that can define a mapping between their manifest and resource formats, and CMAF presentations and the CMAF addressable media objects they include.ISO IEC 23000-19 pdf download.