[theora-dev] Differentiating Video from Audio

[Conrad Parker]

On 26/05/07, Erlend Davidson <E.R.M.Davidson at sms.ed.ac.uk> wrote:
> I am trying to write a "thumbnailer" for the thunar file manager that
> can process .ogg files containing a video stream and produce a thumbnail
> of a particular frame.  The only trouble is telling which files have a
> video stream in an efficient method.  The best I've come up with is
> running ogginfo on every file with the mimetype application/ogg.
>
> Is there a better method?

In general, you would need to read the headers of the various tracks
to see if a video track exists.

For the normal Ogg Theora mapping, the Theora video track must come
first. In that case, the start of the file will look something like
this:

conrad at growl:/tmp$ xxd dbf.ogg
0000000: 4f67 6753 0002 0000 0000 0000 0000 42cb  OggS..........B.
0000010: 4045 0000 0000 d12e e525 012a 8074 6865  @E.......%.*.the
0000020: 6f72 6103 0200 0018 0012 0001 8000 0120  ora............
0000030: 0000 0000 61c1 0000 03e9 0000 0100 0001  ....a...........
0000040: 0200 0000 80c0 4f67 6753 0002 0000 0000  ......OggS......
...

So, you could look for the word "theora" in that specific location.

> I know it has been brought up before on this list and others, but is
> there any possibility of separate mimetypes for audio and video ogg files?

Yes, we have recently been having useful discussions about this and
drafted the following reccommendation:

http://wiki.xiph.org/index.php/MIME_Types_and_File_Extensions

cheers,

Conrad.