[theora-dev] Keyframe seeking in Ogg and spec

Tabuleiro beta at tabuleiro.com
Mon Sep 16 14:03:09 PDT 2002

This might be a stupid question, and forgive me if it really is. But if the
codec is going to pickup information on the granulepos and multiply it by
the frame rate in order to find a reference time why don't we encode the
reference time directly in the granulepos, and save one step? This will
allow variable frame rates if needed. Any reason why this is not a good

On a related note, would it be possible/desireable for an application to
write some sort of "comment" or "extended" info to the headers, which is
optional and would contain information about the position of keyframes, etc?
Higher layers could look for this information in the header, and if present
they could use it to optimize seeks and buffering operations. Do you think
this functionality (which is directly tied to the stream format) is a good
candidate for inclusion in the codec? Maybe the codec code would know how to
decode this optional page, exposing this functionality to all applications?

Mauricio Piacentini

> The timestamps don't have to be explicit in the file; in all the
> schemes monty proposed the absolute frame number can be calculated from
> the granulepos or the granulepos + some state information in the
> decoder. With the frame rate, you can then infer when the frame should
> be displayed relative to the audio playback or whatever clock you're
> using.

<p>--- >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