[Ffmpeg-devel] H.264 decoding bug in either lavc/JM (x264 too?)

Tuukka Toivonen tuukkat
Mon Jul 25 11:53:31 CEST 2005

On Fri, 22 Jul 2005, Michael Niedermayer wrote:

>> I used latest CVS Mplayer and latest SVN x264 (but same results were same
>> with slightly older versions).
>> x264 command line:
>> --bframes 2 --8x8dct --b-pyramid --qp 26 --direct spatial
>> The problem occurs only if using all three options --8x8dct, --b-pyramid,
>> and --direct spatial. Most other options seem not to matter.
>a different number of bframes causes this too?

Yes, I tried 2 and 3 bframes. (with 1 bframe --b-pyramid doesn't have
effect so supposedly the bug goes away. Didn't test...).

>looking just at the diff between the frames i would guess that the motion 
>vectors differ sightly between JM and lavc&x264

So it looks like too: in the JM decoded version parts of the
image appear to shift right around a pixel or so, furthermore,
the image gets fuzzier (at least sometimes).

If you need more test videos, let me know. The bug seems
to occur in most/all of my videos (I might not be able to
reproduce it with standard test sequence like Foreman,
although I didn't try that hard yet), in many it's
much more visible than in this case.

For now, for encoding with x264, --direct temporal
should be used (it increases bit rate around 3% at fixed
PSNR, but removing --8x8dct or --b-pyramid has larger
impact, 4-5%).

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