[MPlayer-users] Re: [BUG?] qprd+vqscale (Was: lavc vs. xvid (and improving lavc quality))

[Jan Knutar]

On Wednesday 02 June 2004 21:04, D Richard Felker III wrote:
> On Wed, Jun 02, 2004 at 05:48:33PM +0300, Jan Knutar wrote:
> > > I never use postproc and I never see blocks. BTW perhaps you're
> > > (stupidly) using vqscale= rather than bitrate/2pass encoding.
> > > There may very well be a bug in the constant-quantizer code
> > > that's ruining quality, since none of us who encode the right way
> > > (2pass) are noticing any problem whatsoever...
> >
> > Lavc makes it easy to shoot yourself in the foot:
> >
> > -lavcopts vcodec=mpeg4:mbd=2:v4mv:trell:cbp:qprd:vqscale=2
> > => Results in broken stream with lots of artifacts
>
> Interesting. Are you using latest cvs? If so, please report the bug
> on ffmpeg-devel.

Reproduced it with cvs up as of 12 hours ago, MEncoder 
dev-CVS-040601-06:51-3.2.2

mencoder orig.avi -ovc lavc -lavcopts\ 
vcodec=mpeg4:mbd=2:v4mv:trell:cbp:qprd:vqscale=2 -o lavc.avi
=> Broken stream

mencoder orig.avi -ovc lavc -lavcopts\ 
vcodec=mpeg4:mbd=2:v4mv:trell:cbp:qprd:vbitrate=8000 -o lavc.avi
=> Ok!

mencoder orig.avi -ovc lavc -lavcopts\ 
vcodec=mpeg4:mbd=2:v4mv:trell:cbp:qprd:vbitrate=8000:vqmin=2:vqmax=2\
-o lavc.avi
=> Ok!

This might be more of a PEBKAC problem though. I'm asking lavc for fixed 
quantizer, at the same time as I'm asking it (afaik) to vary the 
quantizer per MB.