[FFmpeg-devel] [PATCH] Fix for ogg timestamps when packets span multiple ogg pages

David Conrad lessen42
Fri Dec 26 09:16:38 CET 2008

On Dec 1, 2008, at 1:21 PM, Michael Niedermayer wrote:

> On Sun, Nov 09, 2008 at 02:48:01AM -0500, David Conrad wrote:
>> On Nov 6, 2008, at 5:51 PM, David Conrad wrote:
>>> Hi,
>>> The problem with the current code comes from how an ogg page with  
>>> only a
>>> partial packet uses the special granulepos of -1. The granulepos  
>>> needs to
>>> be saved from the last page that completed a packet until the next  
>>> page
>>> that completes a packet, where it is the timestamp of the first  
>>> complete
>>> packet.
>> After looking at ogg granule_position some more, there's another  
>> problem in
>> that Dirac and ogm both assume that the timestamp is the beginning  
>> of the
>> associated packet, wheras Xiph codecs define the granule as the  
>> time after
>> the associated packet is fully decoded (I'm assuming, I've only found
>> Vorbis and Theora to do so explicitly.)
>> Currently the ogg demuxer simply assumes that all codecs use the  
>> latter
>> definition and does codec-specific interpretation of the granule on  
>> the
>> next packet. This causes problems with determining Theora  
>> keyframes, as the
>> frame after the actual keyframe gets the flag.
>> Here's a general fix to always associate the granule and derived  
>> flags with
>> the correct packet, and then delay the interpreted timestamp to the  
>> next
>> packet for Xiph codecs. This fixes ogm timestamps, Theora  
>> keyframes, and
>> allows for correct Dirac timestamps.
> ping, i think the patch is still missing a review from our ogg demuxer
> maintainer

ping x2

(I know M?ns said on irc he'd fix this possibly in a different way,  
but it has been a while)

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