lorenm at u.washington.edu
Fri Apr 2 20:25:50 CEST 2004
On Fri, 2 Apr 2004, Alexei Khlebnikov wrote:
> On Fri, 2 Apr 2004 13:41:13 -0300
> "Pablo Morales" <pablo.morales at abitab.com.uy> wrote:
> > I've got a doubt, I'm encoding using xvid and I found me_quality, range
> > from 0 to 6, how do I interpret that.
> > 0 better quality? or 6 better quality?
> > Using xvid instead livac seems to solve my problem that mplayer uses the
> > bitrate it wants regardless the one I specify in vbitrate=X
> LAVC MPEG4 codec don't use full bitrate if it is not needed, i.e. if maximum
> quality with your settings has been reached. The common advice in this case
> is to increase the resolution to gain more quality.
> If developers don't think its pointless - they can change LAVC codec so that it
> uses P frames instead of (some) B frames, and/or I frames instead of (some)
> P frames if bitrate allows. It will largely increase bitrate and slightly
> improve quality. Maybe XVID does just that.
> (I will certainly be flamed for such suggestion :)
The reason (I infer) that XviD can fill any desired bitrate, and lavc
can't, is that XviD supports quantizer 1 (-xvidencopts
min_iquant=1:min_pquant=1). lavc has a vqscale=1 (constant quantizer), but
doesn't respect vqmin=1 in 2-pass encodes.
Despite what the lavc entry in the manpage says about quant 1 making
little quality difference, XviD with min quant 1 looks much better than
lavc when lavc maxes out with quant 2 at 800kbit/s (and I am encoding at
unscaled dvd resolution).
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