WARP Streaming Format

Packaging Each codec bitstream MUST be packaged in to a sequence of Objects within a separate track. Media tracks SHOULD be media-time aligned. CMAF Aligned Switching Sets meet this requirement. A receiver SHOULD be able to cleanly switch between media tracks at group boundaries. Each group MUST be independently decodeable. Assigning a new group ID to each CMAF Fragment (see Sect 6.6.1) meets this requirement.

Catalog objects The catalog object MUST have a track name of "catalog". A catalog object MAY be independent of other catalog objects or it MAY represent a delta update of a prior catalog object. The first catalog object published within a new group MUST be independent. A catalog object SHOULD only be published only when the availability of tracks changes. The format of the CATALOG object payload is as follows:

WARP CATALOG body

Media format type: this MUST hold the value 0x001 (see ). This value MUST NOT be encrypted.
Version: this MUST be the version of WARP to which the media packaging and catalog serialization conforms.
Parent object sequence: 0 if this object represents an independent catalog or the (Sect 6.2) parent object sequence if this represents a delta update.
Track change count: The number of track changes described by the catalog. A catalog update describing 0 tracks, or deleting all existing tracks, SHALL be interpreted by the WARP client to mean that the publishing session is complete. A WARP client SHOULD process all changes before making a subscription selection.

Each track change is described by a track change descriptor with the format:

Track change descriptor

Full track name length: the length of the full track name field
Full track name: the Full Track Name as defined by (Sect 2.3.1). Track names MUST never be reused. If a track is published and then unpublished, it must be allocated a new track name before it is re-published. A catalog MUST NOT reference itself i.e the the track name must not be "catalog".
Operation: a binary flag. 1 if the track is being added and 0 if it is being deleted. A publisher MUST NOT signal deletion of a track that has not been previously added.
Change payload: depends upon the value of the operation flag. If the operation is a 1 (add), then it SHALL hold an Initialization Header. If the operation is 0 (delete), then it SHALL hold a Deletion Header.

Initialization Header

Init length: the length of the init payload
Init payload: The init payload MUST consist of a File Type Box (ftyp) followed by a Movie Box (moov). This Movie Box (moov) consists of Movie Header Boxes (mvhd), Track Header Boxes (tkhd), Track Boxes (trak), followed by a final Movie Extends Box (mvex). These boxes MUST NOT contain any samples and MUST have a duration of zero. A Common Media Application Format Header meets all these requirements.

Deletion Header

Last group: holds the last Group sequence number published under that track name.
Last object: holds the last Object sequence number published under that track name.

Media Objects Object Delivery Order MUST match the Object sequence number. The media object payload:

MUST consist of a Segment Type Box (styp) followed by any number of media fragments. Each media fragment consists of a Movie Fragment Box (moof) followed by a Media Data Box (mdat). The Media Fragment Box (moof) MUST contain a Movie Fragment Header Box (mfhd) and Track Box (trak) with a Track ID (track_ID) matching a Track Box in the initialization fragment.
MUST contain a single track.
MUST contain media content encoded in decode order. This implies an increasing decoding time stamp (DTS).
MAY contain any number of frames/samples.
MAY have gaps between frames/samples.
MAY overlap with other objects. This means timestamps may be interleaved between objects.

Two options are RECOMMENDED for packaging CMAF content into WARP media objects:

the first is to package a complete CMAF Fragment (see sect 6.6.1) into a single object within each group. This results in there being a single GOP (Group of Pictures) in the media object and a single media object per group.
The second is to package a CMAF chunk (see sect 6.6.5), in which the mdat holds a single frame of video, or sample of audio, into each object and to assign a unique group ID to each fragment. This approach is RECOMMENDED to minimize latency.