[MPlayer-dev-eng] [PATCH] theora support
dvdkhlng at gmx.de
Sun May 11 19:53:50 CEST 2003
Moritz Bunkus wrote:
> Sorry, I've overlooked this thread :/ Yes, the patch is ok, and I've
> committed it to main.
There are two points about demux_ogg.c, which are somewhat ugly:
1. keyframe detection in demux_ogg_seek should use the theora stream
handler's theora-state for properly determining keyframes
theora's method of encoding keyframe information is unbelievably
stupid: the granule pos of theora pckets is calculated like this:
(keyframeNo<<keyframeShift | interframeNo). if the intermediated
frame number `interframeNo' is zero, you know that you've a key
frame. unfortunately `keyframeShift' is NOT FIXED. it's not even
stored directly in the stream header, instead you will have to
calculate the base-2 logarithm of `keyframe_frequency_force-1'
currently my code just calculates `granulePos&0x1FF' and tests
whether it's zero. there's some chance that this will make it skip
some keyframes or sync on a non-keyframe, but won't cause fatal
is there any possibility that `demux_ogg_seek' is called, before
there is a stream handler and a `theora_state' object?
2. i don't understand demux_ogg_build_syncpoints_table, and i'm not sure
that it will work properly with vorbis or theora streams. since
granulepos for vorbis and theora cannot be processed without stream
information (`vorbis_info' respectively `theora_state'), building the
syncpoint table should take place, _after_ stream handlers were
created. currently it seems to be build in `demux_ogg_open', before
there are any stream handlers.
I could try to solve point 1, but this might take me some weeks, since
I'm currently quite busy with other things.
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