[MPlayer-users] MPlayer-1.0pre4 bug with divx4 multipass filter

D Richard Felker III dalias at aerifal.cx
Mon Sep 13 09:40:11 CEST 2004

On Sun, Sep 12, 2004 at 06:05:51PM -0700, Loren Merritt wrote:
> >OK. You can get one yourself, by encoding any file with xvid; I'll post
> >options that will lead to this when encoding the file I'll upload, to be
> >sure.
> I've never encountered that bug in the wild, but...

Because no real release group is so stupid as to encode width%16!=0...

> On Sun, Sep 12, 2004, Vladimir Mosgalin wrote:
> >I always try to keep original dvd resolution, without rescaling, to keep
> >all the details. When width and height aren't multiplies of 8 (16 is too
> >harsh) and I don't want to crop too much, I scale, say, from 708 to 704
> >pixels - eye can't tell the difference.
> There's your problem. After a little fiddling, I can reproduce your
> bug with:
> video resolution not divisible by 16,

704 _is_ divisible by 16 though. And....if Vladimir is such a stickler
for quality, I can't imagine he would encode with a bad width...

> encoded with xvid, (ver: 1.0.2)
> decoded with lavc, (ver: cvs 20040910)
> and a -vf filter chain beginning with spp, unsharp, noise, or delogo
> (don't ask me what's special about those filters)

Can you upload a very short clip for me to see, so I don't have to go
and install xvid?

> BTW, multiples of 16 (not just 8) really are a good idea, and are very 
> cheap compared to everything else you could do to improve video quality: 
> At a given PSNR (and I see no reason why this comparison shouldn't be 
> adequately measured by PSNR), A mpeg4 video with both dimensions 
> non-mod16 takes 5-10% higher bitrate than one cropped, downscaled, or
> even upscaled to the nearest mod16.
> The penalty is about half that if only one dimension is non-mod16.
> Even with 4mv and a resolution divisible by 8, you don't get much of 
> that back (though it depends on the content).
> Maybe I'll get around to posting graphs/writeups of my mod16 benchmarks 
> sometime...

Hahaha, wow, I'm glad to finally have some quantitative figures on
this. The 5-10% figure is huge...I'd like to see some info about test


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