[XviD-devel] xvid + bframes and mplayer/ffmpeg decoding

Michael Niedermayer xvid-devel@xvid.org
Fri, 16 Aug 2002 14:23:15 +0200


Hi

On Tuesday 06 August 2002 18:10, Michael Militzer wrote:
> Hi,
>
> > > > 1) green smearing bug
> > > > If I use the default values in export_xvidcvs and a high bitrate, the
> > > > movie gets more and more green. At low bitrates it is not visible :-)
> > >
> > > IDCT bug, could someone from xvid team try to decode these with the
> > > reference IDCT? in libavcodec it looks bad with the simpleidct & the
> > > reference idct but looks ok with walkens IDCT, iirc xvid uses walkens
> > > idct (=libmpeg2 idct) ...
> >
> > I don't know, i'am not a xvid developer :-)
>
> well, I am ;-)
> yes, we're using the Intel AP922 based idct including walkens rounding
> trick. The green_bug avi decodes fine with xvid, but when using the
> reference idct the evil green becomes also visible... - I wonder what would
> happen if we'd use a different fdct implementation to encode the clip.
> However we would need the original clip for that... Markus, could you
> provide the problematic part in the original format?
btw, it seems that the walken IDCT output all zeros on some non zero inputs 
from green_bug avi, and iirc the mpeg4 std says the encoder shouldnt encode 
blocks with non zero coeffs which are all zero through its own IDCT, perhaps 
that is the cause of the green bug

[...]

Michael