[Theora-dev] want to write comments

Ralph Giles giles at xiph.org
Fri Dec 23 19:43:28 PST 2005

On Sat, Dec 24, 2005 at 12:19:02AM +0100, Rakotomandimby Mihamina wrote:

> I was looking for some command line program similar to vorbiscomment.
> I did not find.

Sadly no such program exists. It is often requested so if you do succeed 
in writing something it will be popular. :)

> I would just try to write a very simple one in C or Python.
> That would be a simple parse of the first bits of the file, if my
> guesses are right. But where could I see the amout of binary bit I
> should open, and how is the signification of any fields I would see...

This is relatively simple. If you want to write in C vorbiscomment 
provides about half of what you need; it just needs to be modified
to handle multiplexed streams.

The theora comment format itself is identical to the vorbis one except 
for the codec header, but it is also completely documented in section 
6.3 of the Theora I Specification (http://theora/org/doc/Theora_I_spec.pdf)

Of course to get at this information and rewrite the stream you will 
have to understand the Ogg bitstream format, documented as RFC 3533
and also at http://xiph.org/ogg/doc/ But there are already libraries
that implement this part. I'd suggest libogg or liboggz in C, or perhaps 
py-ogg2 in Python.

Hope that is helpful,

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