[Matroska-devel] Rejig (for spyder)

spyder spyder at matroska.org
Thu Oct 16 17:09:05 CEST 2003


On Wednesday 15 October 2003 03:37, Steve Lhomme wrote:
> http://forum.doom9.org/showthread.php?s=&threadid=62849&perpage=20&pagenumb
>er=2
>
> Did you check that out ?
It's a transcoder...a quite complex one too since it doesn't fully decode, it 
only drops the bitrate of the streams by adjusting quants etc. I think.  My 
code now lets me get the timestamps off of GOP headers(really useless though) 
and it properly chops the streams into frames.  I can determine frame 
type(I,P,or B), and also framerate, resolution, and aspect ratio of the clip. 
 The problem I have hit now is how to create timecodes for the streams.  
MPEG2 video allows a mixture of 23.976 and 29.97fps video that creates big 
problems for calculating timestamps.  I can break the stream down further to 
determine if the frames are supposed to be 23.976 w/ playback-pulldown or if 
they are real 29.97fps.  Then the new problem is, will decoders care if they 
get 23.976fps timestamps for some frames and then 29.97fps timestamps for 
others.  I think that the decoders don't really need the timestamp info 
anyway as there is none in the raw ES.  I will look at the PS specs today and 
see if we could reuse the timestamps directly from it.  I think it doesn't 
stamp every frame necessarily though.

John



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