[ogg-dev] video chapters and subtitles in ogg containers

Ralph Giles giles at xiph.org
Fri Nov 14 14:04:00 PST 2008

On Fri, Nov 14, 2008 at 12:57 PM, Hans J. Koch <hjk at linutronix.de> wrote:

> Yes, of course. I'm just not sure if such a requirement is covered by
> the spec. After all, CMML seems to be designed as a markup language that
> can be serialized and be spread over the whole stream. But it might be
> possible to define some kind of <chapterlist> tag and require it to
> appear before the beginning of the relevant video/audio stream.

Right. The must-stream thing has lead to everything being spread over
the timeline, but there's an exception in that the vorbis and theora
codecs in Ogg both require configuration data from the head of the
stream. Likewise, each multiplexed data type is identified by looking
at the first page. So the player "already" has to look for and cache
things from the start of the stream, and it's not really an extra
burden to put other things. This is the idea with skeleton, with the
comment packets, etc.

It would be an alternate mode, and a mux tool can convert from one to
the other with no outside information.

On Fri, Nov 14, 2008 at 12:19 PM, Conrad Parker <conrad at metadecks.org> wrote:

> It would work to instead allow all the clips to be in the same packet
> and put that at the start of the stream, with granulepos equal to the
> onset of the first clip (or simply 0).

I don't think it matters how it's packetized, as long as the
granulepos are all 0. Well, aside from the not breaking clip
boundaries. They should probably be marked as headers in the fishbone


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