[theora-dev] A/V sync in Theora

Sam Leitch sam.l at usask.ca
Thu Jun 12 12:07:44 PDT 2003

Why does Ogg\Theora require constant frame rate? From what understand 
lurking for a while, there's no reason to.

Why not encode absolute time in granulepos (or likewise keyframe/offset 

This could really give theora an advantage over the competition. (I'm 
thinking animation)

Ralph Giles wrote:

>> Forget my previous mail, it just starts getting somewhat clearer.  But I
>> think, that at least mplayer employs some kind of A/V sync strategy for
>> AVI which takes information about the interleaving of audio and video
>> packets into account (according to tech/formats.txt).  I frequently use
>> mencoder to record from my v4l tuner card to avi.  Sound comes from my
>> soundcard and is thus guaranteed to not be accurately synced with video.
>> I never encountered A/V desyncs even for long recordings.
> As I understand it, AVI is fixed framerate the way theora is. It's 
> hard to tell without knowing what mencoder is actually doing in your 
> case, but if it's generating proper sync on the encode side there's no 
> reason to expect if can't do the same for theora.
> I didn't understand what you were talking about in my previous mail 
> either. :) Dan explained a bit about the expectations around this. But 
> yes, there's no support for a separate timecode. Theora is fixed 
> framerate, and it's the encoder's job to supply accurately synced data.
> I'm surprised you describe this as a problem with DVD though. I didn't 
> think players were smart enough to adjust playback to match an 
> external sync.
>  -r

Sam Leitch
* * * * * * * * * * * * * * *
Graduate Student
Department of Physics and Engineering Physics
University of Saskatchewan
* * * * * * * * * * * * * * *

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