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

[Hans J. Koch]

On Thu, Nov 13, 2008 at 04:17:04PM -0800, Ralph Giles wrote:
> On Thu, Nov 13, 2008 at 3:59 PM, Silvia Pfeiffer
> <silviapfeiffer1 at gmail.com> wrote:
> 
> > At the moment, Ogg supports two text codecs, CMML and Kate. Both of
> > them are theoretically capable of doing what you want with chapters
> > and subtitles. The biggest problem is player support.
> 
> I also want to mention that Ogg has a natural chapter mechanism, where
> each chapter is encoded separately and the segments are (literally)
> concatenated together. This is legal as long as the stream serial
> numbers are all unique in the chain, and the chapters can be
> identified by metadata changes at the segment boundaries. This has the
> advantage that it can be generated for live streams, and in fact this
> is how song changes are handled in internet radio streams.

Ah, nice feature. This is different from the usual approach known from
DVDs where you have the full list of chapter entry points available from
the beginning. This can't be done for live streams, naturally.

> 
> Again, the biggest problem is player support. Most video players don't
> currently support chained Ogg streams, or do anything useful in the ui
> to show the chapter boundaries.

For a live stream, the player could at least display chapter info. When
recording a stream to disk, it could e.g. offer an option to start a new
file on chapter boundaries. Chapters as known from DVD are probably
impossible since you cannot seek to arbitrary points.

> 
> If you'd like to help, improving player and authoring support for one
> or more of these schemes would be a great place to start. :)

OK. Thanks for explaining this,

Hans