[ogg-dev] What is Kate ?

[ogg.k.ogg.k at googlemail.com]

Hi,

I've posted a fair few questions around about technical points
relating to the Kate codec, and I thought I'd take the occasion
of releasing 0.1.5 to write up a little something to explain what
Kate can do in more practical terms.
I'd love to know if anyone has had a look at the code/format
(which I'm still documenting, sorry) and would have technical
feedback about it. Or any kind of feedback, if you have.

Subtitles:
Kate can be used for movie subtitles - either as text (as created
by ffmpeg2theora) or DVD style pictures:

 - ffmpeg2theora: j was so nice as to include support for Kate
   streams, as read from SRT files.

 - Thoggen: the libkate distribution includes a patch to Thoggen,
   a DVD ripper, to create Kate streams from DVD subtitles.

 - Subtle: I've sent João, the current maintainer, a patch for
   Kate stream support as text. This also includes support for
   multiple streams within an Ogg file, so may be used as a
   starting point for adding CMML support, if anyone fancies
   having a go.

VLC 0.9 can display streams created by ffmpeg2theora and Thoggen
out of the box.
If patched from the diffs included in the libkate distribution,
MPlayer can display those as well.
If patched, the Annodex browser plugin and GStreamer can play
streams created by ffmpeg2theora (eg, text only).

Karaoke:
One of the originally planned uses, Kate can carry glyph positioning
information for a text, to either move a marker along a spline, or
display two parts of a text in different styles (typically color).
This will however require more in depth rendering, as I've started
doing with the rendering library I'm working on (see below). Proof
of concept works, but needs refinement.

Graphical overlays:
Kate can carry images and animated attributes such as position,
size, etc. Moving overlays can thus be superimposed onto a video,
allowing TV style effects. When the rendering library is fleshed
out a little more, I plan to add features to the Kate format such
as rotation, etc. I am still undecided whether to include or not
animations, since Ogg/MNG does not seem totally dead yet. Animated
pointers for karaoke mode would be a nice thing to have though,
and difficult to do with a separate Ogg/MNG stream as it has to
match the text geometry, so I'm keeping this on the back burner.

Rendering library:
I am working on a rendering library (not yet released, as it only
supports part of the current Kate stream features, and is a little
buggy still) which can render a Kate stream using Pango and Cairo.
The idea is to add consistent rendering ability to all media players,
without each having to reimplement the same code over and over.

So there's still a lot to do.

But now I can view my small DVD collection in Theora with subtitles,
so I'm happy :)

Thanks