[Matroska-devel] Re: Re: MPEG2 in MKV!
spyder at matroska.org
Thu Oct 30 18:56:25 CET 2003
> I copied and pasted what you put in IRC.
> [00:11] <spyder482> here's the way it actually works according to mpeg
> docs: [00:12] <spyder482> [A][B][Cr][Dr] yields [Aa][Bb][Cc][CD][Dd] on
Then I was wrong :P
> > Bad idea to remove the pulldown. MPEG decoders expect constant framerate
> > and you can't change the framerate to 24fps becasue you would need to
> > drop some frames which would break the encoding scheme of mpeg2. (ie,
> > removing data referenced by other frames)
> We just need to change to framerate as specified in the Sequence headers.
No...then you introduce sync errors. Not all files will be played in crappy
DirectShow filters. MPEG video has a framerate for a reason, it's not just
informational. If you change the framerate but leave more frames then you
intorduce sync problems. If you drop the extra frames then you break the
stream. Besides, we shouldn't have to destroy any mpeg compliance just to
put the stream in MKV. As I said before, the ONLY thing allowed to change
from sequence header to sequence header is the QUANTIZERS! You can't change
framerate, resolution, colorspace, progressive vs. interlaced etc.. Only
those 128 bytes for the quantizer are allowed to change. Otherwise the
stream is b0rked and no longer spec compliant.
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