[theora-dev] A/V sync in Theora

Ralph Giles giles at xiph.org
Thu Jun 12 09:52:57 PDT 2003

On Thursday, June 12, 2003, at 05:30 pm, David Kuehling wrote:

> Is ist valid for Vorbis packets to drift the granulepos to compensate
> for A/V sync?  That would mean that granulepos does not represent the
> number of actually played samples any more.  Seems like an ugly hack.

Yes it does. Counter to spec too, so I don't recommend it.

I guess I'm perplexed from the other end. The vorbis granulepos is in 
number of samples, so multiply by the sample rate to get a timestamp. 
The theora granulepos can be converted to the frame index, which you 
multiply by the framerate to get a timestamp. Those timestamps should 
align at playback. It's up to the player to work out how to make that 


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