[MEncoder-users] [BUG]A-V desync with pullup,softskip and b-frames

[Corey Hickey]

[sorry to bug you personally, Michael, but I don't know if you subscribe
to mencoder-users and I thought you might be interested]


I'm having some trouble with mencoder creating files with audio about
200ms or 100ms early. This only occurs when I use b-frames, or pullup
and b-frames together; removing either one gets rid of the desync.

I'm expecting Rich and Michael to tell me b-frames are evil. :) ...but
nevertheless they improve quality slightly and I've been using them up
until now. I'm reporting this on the chance the bug is fixable, or at
least worth fixing. If not, at least it's on the record for the benefit
of other users.

The video is 24000/1001 fps progressive during the test section (1800
frames). The source is a DVD, and I am uploading the first part.
Strangely enough, I wasn't able to reproduce the same effect on a
different DVD. I'm uploading all files mentioned to
ftp://ftp.mplayerhq.hu/MPlayer/incoming/desync/ (but it'll take a
while). The output files are bzip2ed and attached, as well.

The quick breakdown is that enabling b-frames by themselves seems to
cause slight desync, and using softskip,pullup makes the desync worse.
Using softskip,pullup makes the desync worse, but doesn't seem to affect
the sync without b-frames. (yes, I know, the easy solution is just to
avoid b-frames, but still...)

----
mencoder test.vob \
-ovc lavc -oac copy -ofps 24000/1001 -frames 1800

file: base.avi
output: base.txt
result: A-V sync is good

----
mencoder test.vob -vf pullup,softskip \
-ovc lavc -oac copy -ofps 24000/1001 -frames 1800

file: pullup-softskip.avi
output: pullup-softskip.txt
result: still good

----
mencoder test.vob -lavcopts vmax_b_frames=1 \
-ovc lavc -oac copy -ofps 24000/1001 -frames 1800

file: bframes.avi
output: bframes.txt
result: audio about 100ms early

----
mencoder test.vob -vf pullup,softskip -lavcopts vmax_b_frames=1 \
-ovc lavc -oac copy -ofps 24000/1001 -frames 1800

file: pullup-softskip-bframes.avi
output: pullup-softskip-bframes.txt
result: audio about 200ms early


I also tested with only softskip alone instead of pullup,softskip, and
there was no noticable difference compared to not using any vfilters at
all. That is, softskip doesn't seem to change anything.


System info:
MEncoder dev-CVS-041009-13:05-3.3.4 (C) 2000-2004 MPlayer Team

AthlonXP 3000+
Linux 2.6.9-rc2-mm4
Debian Sarge (testing)
libc6 2.3.2
GNU ld version 2.15
gcc version 3.4.1 (Debian 3.4.1-4sarge1)
GNU assembler 2.15



Thanks,
Corey
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