[theora-dev] question about ogg mapping

Dan Miller dan at on2.com
Thu Jun 12 08:34:51 PDT 2003

right, my issue is that we're using granulepos somewhat stragely right now with certain bits indicating keyframes, etc.  That scheme seems to break under the scenario of >1 frame/page.

I'm concerned about this as we're about to release a supposedly stable bitstream, and ffmpeg & mplayer are already supporting the format with more to come hopefully.

<p>-----Original Message-----
From:	Mauricio Piacentini [mailto:mauricio at tabuleiro.com]
Sent:	Thu 6/12/2003 10:49 AM
To:	theora-dev at xiph.org
Subject:	Re: [theora-dev] question about ogg mapping

And how would you get the absolute time for each frame in this scenario
(multiple packets per page?) This is absolutely necessary for a player to
operate correctly. Or is there anything I am missing, like a way to get the
absolute position from the packet data and not the page granulepos?


> Yes that's fine. There wouldn't be any point to having pages if they
> weren't different from packets, and as you suggest, it's necessary to
> keep the overhead down.
> > If I shove a few frames into a page, how does this affect the
> > granulepos stuff?
> It's actually pages that have granulepos. The granulepos in the packet
> structure is just how they're passed to the ogg layer. Granulepos is
> 'the total samples encoded after including all packets finished on this
> page', so libogg sets the page granulepos to the greatest granulepos of
> the packets that ended on that page.

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