Annex A.5: Does track_ID uniqueness hold for CMAF ISO BMFF Tracks?

cta-wave / CMAF-Byte-Stream

For discussion of CMAF Byte Stream format

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Annex A.5: Does track_ID uniqueness hold for CMAF ISO BMFF Tracks? #15

Closed haudiobe closed 3 years ago

haudiobe commented 3 years ago

The track is:

A CTA-608 closed caption service: the string “cc” concatenated with the decimal representation of the channel_number
A CTA-708 closed caption service: the string “sn” concatenated with the decimal representation of the service_number field in the ‘Caption Channel Service Block’
Otherwise, the decimal representation of the track_ID of a TrackHeaderBox (tkhd) in a TrackBox (trak).

Editor's Note: Assuming true, but does track_ID uniqueness hold for CMAF ISOBMFF tracks?

technogeek00 commented 3 years ago

My last call notes had the statement that track_ID uniqueness is not guaranteed with CMAF, but this was going to be checked further. Did anyone have time to follow-up?

sdp198 commented 3 years ago

CMAF requires track_IDs to be the same across all Tracks in a switching set, but does not place any requirement outside of that. So two different switching sets can (and often do) use the same track_ID. In my experience almost all tracks use track_ID=1, since the packager is only putting one track in each file it has no reason to do anything other than start at 1.

technogeek00 commented 3 years ago

@sdp198 thanks for your comment, this aligns with my own experience and expectations otherwise the independent creation of tracks needs a centralized orchestrator which may be counter to workflow operations.

From the perspective of setting ids on Video/Audio/Text tracks it might be best to require all ids to either be:

uniquely generated at track creation time by the track management engine
supplied by the logical player as part of the track creation

haudiobe commented 3 years ago

AHG Call 2020/10/19: addressed in revised draft. Unless any comments are received, the issue will be closed by the next meeting.

haudiobe commented 3 years ago

Implemented: https://1drv.ms/w/s!AiNJEPgowJnWgqsz3EFQvnMD7BhN0w?e=42BwJJ