[theora] Searching for keyframes

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

> I have a routine that searches an Ogg stream for Theora keyframes.  I am
> using
> theora_decode_packetin on each packet which is pretty slow.  Is there a way
> to just extract the granulepos from the stream without decoding all the

When you get a page, you can get its granulepos field, and from there you
should be able to deduce if a keyframe has happened between (last you
checked) and (at or before the last packet which finished in that page).