[MPlayer-cvslog] CVS: main/libmpcodecs ve_lavc.c,1.111,1.112

[Guillaume Poirier]

Hi,


On Thu, 3 Mar 2005 16:26:42 -0800 (PST), Loren Merritt
<lorenm at u.washington.edu> wrote:
> On Thu, 3 Mar 2005, Guillaume Poirier wrote:
> > On Wed, 2 Mar 2005 14:02:54 -0800 (PST), Loren Merritt wrote:

[..]


> >> (BTW, I recommend vqcomp=.6 or .7 in lavc too, in which case CQP 1st
> >> pass becomes good there too.)
> >
> > That's interesting... Taking other people's experience into
> > consideration, I always set vqcomp=.6 too, but I never understood what
> > the option was really doing for its documentation is very terse.
> > Here's what it reads:
> > vqcomp=<value>
> >       Quantizer compression, depends upon vrc_eq (pass 1/ 2) (default: 0.5).
> >
> > Could you maybe enlight me a little bit Loren?
> > Of course, your explanation will certainly make its way to the man page ;-)
> >
> > Also, when you say that increasing a bit vqcomp makes constant quant
> > first pass acceptable, does this parameter influence the first or the
> > 2nd (and subsequent) pass? The way I understand it makes me think that
> > it kicks in in 2 and up passes, but that's pure guess. I'm not the
> > video processing expert here....
> 
> (For the purpose of this explanation, consider "2nd pass" to be any beyond
> the 1st. The algorithm is run only on P-frames; I- and B-frames use QPs
> based on the adjacent P. While x264's 2pass ratecontrol is based on lavc's,
> it has diverged somewhat and not all of this is valid for x264.)

[..]

Thanks a lot for you nice, clear and detailed explanation. As I said
earlier, I'm working on improving MEncoder's XML encoding guide. I
added an "encoding options" entry that will somewhat collect some of
you explanation as thei really deserve to be put in a more
appropriate/official place.

I also plan to add the advices you wrote there:
http://forum.zhentarim.net/viewtopic.php?p=237 Is that Ok with you?
I think it would be a good thing to do as other external links that
http://www.mplayerhq.hu/DOCS/tech/encoding-tips.txt refers to are
dead, just like lavc tests
http://rguyom.chez.tiscali.fr/libavcodec_tests.html .

Thanks a lot,

Regards,

Guillaume