[MPlayer-users] x264 and loss of sync with B-frames

[Rich Felker]

On Mon, May 16, 2005 at 12:49:23AM -0400, Jason Tackaberry wrote:
> Using mencoder and x264 from tonight's cvs/svn.  I've been experimenting
> with x264, and I've noticed that when I use B-frames I get output whose
> number of frames increases with the number of B-frames I use, which
> seems to directly affect A/V sync.
> 
> Here's the mencoder command I'm using:
> 
>    mencoder -dvd-device I_Robot.dvd dvd://1 -vf hqdn3d=2:1:2,crop=704:368:8:54  \
>    -ofps 24000/1001 -oac copy -ss 6:00 -frames 250 -ovc x264 -x264encopts \
>    bitrate=1500:pass=$PASS:4x4mv:frameref=6:bframes=10 -o clip.avi
> 
> Setting bframes=0 results in a clip.avi which is perfectly in sync.
> Setting bframes=1 causes the clip to become slightly out of sync but not
> very perceptible.  Setting bframes=10 or 15 causes it to become
> noticeably out of sync.
> 
> Am I doing something wrong?  Or is this a bug in mencoder or x264?  Let
> me know if you'd like me to upload the clip.

I think it's a bug, and one that's fairly hard t oovercome without
ugly hacks or large architectural changes. My advice is and always has
been: do not use B frames. They're nasty and cause all sorts of
problems, and do not significantly improve compression.

Rich