[theora] How to seek theora streams

[Chris Pearce]

Seeking robustly is hard.

A good place to start is by looking at liboggz's seeking code in 
oggz_seek.c, oggz_bounded_seek_set(). Conrad also has a seek-rewrite 
branch in his git repository which cleans up that code significantly.

An example of a program which uses liboggz's seeking is oggplayer. It 
uses liboggplay which in turn uses liboggz to seek:
http://www.bluishcoder.co.nz/2009/03/oggplayer-simple-ogg-player-using.html

However, liboggz does not seek back to the theora keyframe prior to your 
seek target. So if you use oggz_seek() and just start decoding from 
there, you'll get garbage in your theora frames until libtheora hits a 
keyframe packet.

This thread has some discussion of some solutions for this:
http://lists.xiph.org/pipermail/theora/2009-July/002544.html

Do you need your seek to be millisecond accurate? If not, you can just 
do a rate-estimation (e.g. seek file to offset (file_size / 
media_duration) * seek_target), ogg_sync_pageseek(), and then decode 
forward from there. VLC takes this approach, and it works well enough.


All the best,
Chris Pearce.


On 20/08/2009 8:05 a.m., Manolache Adrian wrote:
> I need to be exposed to a way of seeking theora streams. I have
> repeatedly found the same question asked on a different forums but could
> not find an answer. I'm working on a game and started integrating video
> with theora, the sound works just fine with ogg/vorbis(i find it easy to
> seek using ov_raw_seek for audio files). Could someone please point me
> to some example/code of how can i seek with theora?
>
>
>
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