[MPlayer-users] Re: Fast recompress

[D Richard Felker III]

On Wed, Jul 23, 2003 at 09:12:44AM +0200, Stefan Seyfried wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> rbtq7ol02 at sneakemail.com writes:
> 
> > not converting to RGB and back.  My understanding is that the situation is 
> > similar in mencoder - colorspace conversions are already performed only when 
> > necessary, which should mean that most of the time they're not performed at 
> > all.
> 
> Maybe it would also be possible to skip the quantizing stage of encoding
> if one wants to crop black bars when recompressing a movie, since the
> actual picture stays the same, the quantizers and motion vectors should
> also stay the same. This would probably only work when using the exact same

Motion vectors would NOT stay the same. That's the whole reason why
leaving black borders in is a horrible horrible idea. If you have
black borders, motion estimation will NOT work at the edges of the
image, so you'll need lots of bits to encode, or else get nasty
artifacts.

Anyway, the quantizers could be kept, but that does NOT allow you to
skip quantization, since after redoing motion vectors, everything else
has to be redone too!

Rich