theora - Feb 2007 - Number of frames

Hi All 

I am coding an application capable of playing theora movies using libtheora and
libogg.
Now, I need to know the duration of a theora movie in frames.

I seem to be unable to find that information in the using either libtheora or
libogg.
Google gave a hit proposing to read the file backwards till the magic
"OggS" could be
found and then scan forward to the framenumber field could be found.
Another way would be to decode all frames to the end of the move, and then count
the frames as I
decode.

Neither approaches seem like the right one.

Can anybody tell me if I have missed something obvious or propose a third and
better approach?

Regards, 
   Morten

On 2/12/07, Morten Winkler J?rgensen <morten@thorsen-consulting.dk>
wrote:
> Hi All
>
> I am coding an application capable of playing theora movies using libtheora
and libogg.
> Now, I need to know the duration of a theora movie in frames.
>
> I seem to be unable to find that information in the using either libtheora
or libogg.
> Google gave a hit proposing to read the file backwards till the magic
"OggS" could be
> found and then scan forward to the framenumber field could be found.
Hi Morten,

That's approximately right. Because Ogg is designed as a streaming
format, it doesn't contain information about the length of the stream
in the header.

So basically, you need to find the final frame in the file, and get
the frame number of that. You'll also probably want to read the start
of the file, to check what frame number it starts from (it might be
non-zero if the file has been captured from a stream, or edited out of
a larger file, etc.)

Mike