[Matroska-devel] MPEG2 in MKV!

spyder spyder at matroska.org
Thu Oct 30 16:59:41 CET 2003

> i was recently pointed to the 'codec state' element that is already in
> the MKV specs, could this element be used to store the sequence headers
> maybe ? With 'codec state' , IIRC, the idea behind it was to be able to
> change the picture resolution, colourspace etc. during playback and
> within one video stream, without creating several streams and appending
> them. Only thing that couldnt be changed was the codec itself AFAIK.
> Basically, if the parser finds a 'codec state' element in the stream, it
> has to reinitialize the codec completely, dont know if its ever possible
> to play such a stream on DirectShow, maybe only if we finally implement
> a resizing filter into the splitter, dont know, the DShow experts to
> clarify please.
> This leads me to another problem : you are aware that we can not make
> and release a MPEG2 decoder specifically for MPEG2 coming from MKV, do
> you ? Is there any chance to reproduce at least an MPEG2 Elementary
> Stream from the MPEG2 track in MKV, such that external existing decoders
> can play the stuff, like ffdshow etc. ? Please tell me its possible and
> you didnt forget that  :-) .....

Codec state should be what we are looking for I guess.  The codec won't have 
to be reinitialized though, only fed the new sequence header.  We weren't 
planning on making an MPEG2 decoder.  It should be able to be fed to any 
mpeg2 video decoder.  I am not sure exactly how those work but Gabest would 
know since MPC includes one ;) 

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