[theora-dev] Keyframe seeking in Ogg and spec

Monty xiphmont at xiph.org
Mon Sep 16 14:04:06 PDT 2002

> > One problem I see with your proposed implementation is that it does not
> > specify how audio and video would be synchronized, since there are no
> > absolute time stamps for the video frames. 

Yes, there are absolute timestamps.  Did you read the whole thing?

> > So it is difficult to account 
> > for audio latency on different systems, much like when you play an AVI 
> > file. 
> > Ideally it would be wonderful to have timestamps that could be 
> > used to synchronize audio and video in a meaningful way, and if I 
> > understand it correctly the proposed granulepos formats do not address 
> > this.

They certainly do.

The whole point is not carving a new timebase system into the lowest
Ogg layers every time a code appears with a system that doesn't fit.
All one needs to do is ask a codec 'I have this granulepos, convert it
to an absolute timestamp, please'.  This aspect of a codec is
required.  The stream handlers will always know absolute time
position.  And it will still work in the future even if we have a
video codec with no concept of fixed framerate.

[You're even welcome to just use the granulepos as a straight
timestamp in future codecs if you want... but that's specific to the codec]

> > In Ogg, things like the duration of the whole video could come in the
> > first
> > page (you could send -1 for live transmissions, for example).

...or we can have the system we have now, which always works, is easy
to use, and doesn't require supporting an additional optional
mechanism that adds no functionality.

--- >8 ----
List archives:  http://www.xiph.org/archives/
Ogg project homepage: http://www.xiph.org/ogg/
To unsubscribe from this list, send a message to 'theora-dev-request at xiph.org'
containing only the word 'unsubscribe' in the body.  No subject is needed.
Unsubscribe messages sent to the list will be ignored/filtered.

More information about the Theora-dev mailing list