theora - Aug 2011 - Changing frame rate in an ogg

Hi

 

I'm trying to understand how to change framerate in an ogg/theora file.
I'm
recording a stream from a chat (RTP/THEORA) but frame rate of recorded
stream is not correct.

Reading theora documentation it seems that frame rate (FRN and FRD) only
affects granulepos/timestamp but changing it (manually) in the ogg files
causes bad decoded frames while playing (I've also tried other ogg videos).

Obviously I'm missing something, is there some way to change frame rate (I
need to slow the playing of file) using ogg or oggz api?

 

Thank you,

 

Stefano




 

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On 25 August 2011 23:57, Stefano Luceri <stefano.luceri at agilex.it>
wrote:
> Reading theora documentation it seems that frame rate (FRN and FRD) only
> affects granulepos/timestamp but changing it (manually) in the ogg files
> causes bad decoded frames while playing (I?ve also tried other ogg videos).
Two things:

Theora is strictly fixed frame rate. If the incoming video data is not
at a fixed frame rate, then your encoder will need to check against
the playback clock and duplicate or drop frames to make it so. Since
RTP has per-packet timestamps, this can be relaxed to simplify the
sender implementation, but once saved to an Ogg file, all players will
treat the stream as fixed frame rate. This is likely the reason your
file doesn't behave as you expect.

If you just want to adjust the frame rate of an already saved file,
you could try the little 'rogg_theora' utility I wrote.

  http://downloads.xiph.org/releases/rogg/rogg-0.4.tar.gz

Be aware that it doesn't support Ogg chains or files over 2 GB on 32
bit systems.

 -r