[ogg-dev] handling multitrack Ogg

Monty Montgomery monty at xiph.org
Tue Feb 2 05:33:45 PST 2010

> In discussions with the video accessibility subgroup of the W3C HTML
> working group, we are currently looking at how to deal with multitrack
> video, e.g. such video that has a main video and audio track, plus
> e.g. a sign language video track, an audio description audio track, a
> caption track and several subtitle tracks in different languages.
> (i.e. several theora, several vorbis and several kate tracks)

Hooray!  This was always an intended use of the system, even if the
metadata representation of the track structure was never set.  I
didn't want to get too far into it without practical use cases people
could present that they actually needed.

> Right now, I can see two different systems: the order in which their
> BOS pages are given in the Ogg header part - or the order in which the
> serial numbers go, when ordered. Alternatively, we can introduce an
> explicit track ID and order by that number.

Right, add an explicit mapping of the indirection.

Well, any of the above requires an addition to best practice.  Oggk's
right about 'no tool would automatically respect any of the above
right now', so we get to decide but then we also have to gently coerce
regardless the decision.  Thank god there are no good tools for
editing as yet!

I don't object to any of those proposals. They seem pretty
interchangable.  So long as its clearly documented and orderings, when
they matter, are explicitly defined in the metadata.


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