AW: [theora-dev] Keyframe seeking in Ogg and spec

Waldvogel, Tobias tobias.waldvogel at
Mon Sep 16 13:09:08 PDT 2002

Hi all,

> One problem I see with your proposed implementation is that it does
> specify how audio and video would be synchronized, since there are no
> absolute time stamps for the video frames. So it is difficult to
> for
> audio latency on different systems, much like when you play an AVI
> 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
> correctly the proposed granulepos formats do not address this.

That's true. On the other hand the timing information is handled by the
codec layer and not on the Ogg layer. So it is sufficient if the codec
can reconstruct the time information. Anyway it would be more convenient
to have the same time base.
In Ogg DSF I convert samples/frames to a reference time to get them in
sync. Therefore the number of frames/sec is stored in the header as the
number of samples in "vi.rate"

> 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).

There is no need to store the length. If it is just one stream you can
go to the end of the file, take the last "granulepos". You have just to
convert it in to a meaningful unit like time.

Tobias Waldvogel

<p>--- >8 ----
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