ogg dev - Nov 2008 - video chapters and subtitles in ogg containers

Hi,

(odd, I did get this reply for Silvia, but not the original post)
> There is CMML and kate support in vlc, and kate in mplayer though I am
> not sure how it is displayed on-screen. Subtitles may display, but
> chapter markers, I am not so sure about.
Would you mind expanding on what chapters are, and what you'd expect
to be able to do with them ?
> There is an old python script for cmml at
> http://svn.annodex.net/scripts/trunk/subtitles/script-subrip2cmml.py .
> I'm not sure something like this exists for kate.
> But it should not be too hard to write one.
kateenc (a tool bundled with libkate) can convert a srt file to a Kate stream,
which can then be multiplexed along with a Theora video (and other Kate,
Vorbis, etc streams).

On Fri, Nov 14, 2008 at 10:48:46AM +0100, ogg.k.ogg.k at googlemail.com
wrote:
> Hi,
> 
> (odd, I did get this reply for Silvia, but not the original post)
Hmm, it was properly CCed to the list.
> 
> > There is CMML and kate support in vlc, and kate in mplayer though I am
> > not sure how it is displayed on-screen. Subtitles may display, but
> > chapter markers, I am not so sure about.
> 
> Would you mind expanding on what chapters are, and what you'd expect
> to be able to do with them ?
Chapters are a list of timepoints stored in the metadata. They are an
information for player software that is usually used to allow the user
to jump to certain significant points within a stream. This probably
only makes sense for media that has a start point (t=00:00:00.000) and a
duration, not for continous streams like web radio.
Player software might need to take additional measures, e.g. round the
time up or down to the nearest keyframe.

An important factor is the ability to seek an arbitrary point within a
stream. Depending on the codec used, this might be a more or less costly
process. Some media (like DVD) slightly modify their stream encoding to
simplify seeking.

Chapters like this are mainly used on video DVDs, but are also defined for
SVCD and OGM containers. My personal use is watching movies from SDcard
or harddisk. I'm the type of guy who often wants to watch only some
parts of a movie, and chapters greatly simplify finding a certain scene
(or skip one that is too exciting...).
> 
> > There is an old python script for cmml at
> > http://svn.annodex.net/scripts/trunk/subtitles/script-subrip2cmml.py .
> > I'm not sure something like this exists for kate.
> > But it should not be too hard to write one.
> 
> kateenc (a tool bundled with libkate) can convert a srt file to a Kate
stream,
> which can then be multiplexed along with a Theora video (and other Kate,
> Vorbis, etc streams).
That's an interesting hint. I'll have a look at that.

Thanks,
Hans

>> (odd, I did get this reply for Silvia, but not the original post)
>
> Hmm, it was properly CCed to the list.
Yes, I found it in the spam bucket for some reason...
> Chapters are a list of timepoints stored in the metadata. They are an
> information for player software that is usually used to allow the user
> to jump to certain significant points within a stream. This probably
I don't think anything currently in Ogg can do this. The closest I can
think of is CMML's clip concept, but you'd still have to parse the
entire
stream to find them all.
One could build an index of them to place them in a Skeleton message
header though, but there is nothing to do that AFAIK.
> Chapters like this are mainly used on video DVDs, but are also defined for
> SVCD and OGM containers. My personal use is watching movies from SDcard
> or harddisk. I'm the type of guy who often wants to watch only some
> parts of a movie, and chapters greatly simplify finding a certain scene
> (or skip one that is too exciting...).
If you are transcoding a DVD, you might want to look at the diffs directory
in libkate, there is a patch to Thoggen (Linux based DVD transcoder) that
automatically converts DVD subtitles to Kate streams, though it also requires
a set of patches to GStreamer (also found in the same directory) to be applied.