[MEncoder-users] Why does FFMPEG encode without sync problem but Mencoder cannot?

[David Smith]

I'm using WindowsXP, and I ran the same .mov and .wmv videos against
Mencoder and FFMPEG to turn them into Flash (flv) using the same bitrates
and no other parameters, and not only did FFMPEG convert it about about
twice the speed, the audio and video are in perfect sync, while Mencoder's
is not.  What gives?  I ran them independently, and with no other services
going in the background.

ffmpeg -i videoIn.wmv -b 300k -ab 32k -ar 22050 videoOut.flv
mencoder videoIn.wmv -o videoOut.flv -oac mp3lame -lameopts abr:br=32 -srate
22050 -ovc lavc -lavcopts vcodec=flv:vbitrate=300 -of lavf

Both of these resulted in the same file size, which I expected.

THAT SAID, if I run mencoder with the -vf harddup switch my audio/video sync
are fine, but it takes much, much longer to encode (like 7x's as long), and
the file size is almost 2/3's larger.  I'm sure it's because it's encoding
the duplicate frames, but why would this be?  I've also experimented with
fps in and out, but the only option that works is harddup.  How come FFMPEG
can sync without a harddup type option?