[MPlayer-users] MPlayer-1.0pre4 bug with divx4 multipass filter
lorenm at u.washington.edu
Mon Sep 13 03:05:51 CEST 2004
On Mon, 13 Sep 2004, Vladimir Mosgalin wrote:
> On Sun, 12 Sep 2004, D Richard Felker III wrote:
>>> There are another problems when decoding with lavc. When running
>>> "mplayer xvid-encoded-file.avi -vf noise=12uah", mplayer writes
>>> "vf.c: have to REALLOCATE buffer memory :(" several times a second,
>>> and often, but not always (in about 50% cases) segfaults on exit (in
>>> uninit_vcodec), and then hangs. Interrupting doesn't help, only sigkill
>>> does. Also, several upper lines get distorted.
>> this has nothing to do with xvid/lavc...and in fact it should never
> But it has.
>> happen. if you see a crazy bug like this, please upload samples and
>> make a bug report! obviously no one else has experienced this problem,
>> or at least none of the developers.
> 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
I've never encountered that bug in the wild, but...
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
video resolution not divisible by 16,
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)
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
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