[MPlayer-users] A/V sync with two-stage encoding
Ian Smith
the.pond at dsl.pipex.com
Wed Apr 28 21:26:19 CEST 2004
For a while now I have been trying to perfect a two-stage process
whereby I record a "master" high-quality copy from my TV card, then
"mix-down" to a 1Mb/s AVI file.
This way I can do a two-pass on the second stage to make best use of the
lower bitrate, and I can also set my cropping rectangle exactly where I
want it.
I have tried using high-rate mjpeg/mpeg4 encodings to achieve the master
quality I need, but when I re-encode to the lower rates I always get A/V
sync drift.
If the scenario above doesn't make any sense, picture the master as a
freshly-ripped VOB file, (which incidentally works fine with no sync
problems).
On seeing the lossless ffv1 encoder for the first time, I just had to
try it! So I made a master recording using the command line:
/usr/bin/mencoder -tv driver=v4l:width=768:height=576:input=0 tv:// -ovc
lavc -lavcopts vcodec=ffv1:vstrict=-1 -oac copy -vop scale=384:288,pp=lb
-endpos 00:05:00 -o grabbed.avi
Lovely! Now I do a two-pass:
/usr/bin/mencoder grabbed.avi -ovc lavc -lavcopts
vcodec=mpeg4:v4mv:trell:cbp:mbd=2:vbitrate=917504:vpass=1 -oac copy -o
/dev/null
/usr/bin/mencoder grabbed.avi -ovc lavc -lavcopts
vcodec=mpeg4:v4mv:trell:cbp:mbd=2:vbitrate=917504:vpass=2 -oac mp3lame
-lameopts cbr:br=128 -o compressed.avi
and the dreaded A/V sync lag is back! Any suggestions, or am I just
doing something wrong? I don't think I am, because there is no sync
problem if I use an MPEG2 master source.
Note that I only encode the audio during the second pass.
--
------------------------------------------------------------------------
Ian Smith
Worst . . . signature . . . ever !
More information about the MPlayer-users
mailing list