[mythtv] A prelude to transcoding MPEG2->MPEG2

Geoffrey Hausheer ou401cru02 at sneakemail.com
Sat Dec 6 09:31:58 EST 2003


On Sat, 06 Dec 2003 06:29:29 +0100, "Kenneth Aafl°y" said:
> It's 6:30 in the morning here, so I hope I did not catch the point.
> 
> If we where to cut between two keyframes, why not just decode the frames
> from the first keyframe and until now, and reencode them to the frame we
> want to be at. What to do with the remaining frames would offcourse be
> codec independentent (tm), as we can't know what state the codecs want
> after such an operation. The most keen solution would be to encode also
> the rest of the non-i-frames after the frame we just handleded (won't be
> many anyway..)..

Sure sounds easy doesn't it?  Unfortunately, this is non trivial.  As
others have mentioned, just chopping to real i-frames is much more
difficult than it sounds.  Reencdoing will make it harder, becasue you
need to generate a valid GOP that looks exactly like the other GOPs,
otherwise you risk compatibility issues.  I think I'll start with
chopping down to the nearest I-frame, and if that actually works, then
perhaps we'll try adding a encoder into the mix.

Don't expect anything soon though.  This is not a trivial task (which is
why it hasn't been done already)

.Geoff



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