[MEncoder-users] At wit's end - MEncoder can't keep AV sync, others can

[Steve West]

Pulling my hair out over this one.  Simply cannot make MEncoder maintain audio/
video sync with a certain video that numerous other programs play AND transcode
correctly.  Hoping the experts here might help: and possibly, this may even be a
MEncoder bug, so, another reason to bring it up here.

Source material is a VOB from a DVD+RW recorded in a Pioneer set-top DVD recorder
from American 525i (480i) NTSC VHS.

All the following leave me with proper A/V sync:

* That .VOB played with VLC 1.0.5
* That .VOB played with Gabest's Media Player Classic 6.4.9.1r89
* That .VOB played in MPlayer for Windows (r31027 from http://mulder.at.gg/)
* That .VOB converted to an XviD+MP3 .avi with AutoGK 2.55
* That .VOB converted to an x264+AAC .mp4 with Womble MPEG Video Wizard DVD 5.0

All the following leave me with broken A/V sync with audible skipping:

* That .VOB converted to an x264+MP3 .avi with MEncoder r31139 (from http://oss.netfarm.it/)

The command line I started off with:

mencoder.exe input.vob -ofps 29.97 -vf scale=640:480,denoise3d,softskip,harddup -nosound -ovc x264 -x264encopts bitrate=1200:pass=1 -o nul
mencoder.exe input.vob -ofps 29.97 -vf scale=640:480,denoise3d,softskip,harddup -af volnorm=1 -oac mp3lame -lameopts abr:br=192 -srate 32000 -ovc x264 -x264encopts bitrate=1200:pass=2 -o output.avi

When that failed, I RTFM and wound up trying (with absolutely no luck) all the
following changes to the commandlines above, one at a time (i.e. each change was
undone before the next was tried):

* Replacing -nosound on pass1 cmdline with same audio params from pass2 cmdline
* -ofps 30000/1001 instead of -ofps 29.97
* Omitting -ofps entirely
* Adding -mc 0 -noskip -skiplimit 0, and :force_cfr: to x264encopts
* Adding just force_cfr to x264encopts
* Adding just -mc 0 -noskip
* Adding just -noskip
* Removing softskip
* Removing harddup
* Removing denoise3d

Nothing worked.  Same bad sync and audible skipping as before, only sometimes with
the A/V sync even worse.

So I went back to my original command lines as seen above, and decided to try
feeding MEncoder different input -- by (one at a time):

* Opening my .VOB and re-saving (stream copy) as .MPG with Womble (this strips all
  VOB internals and yields "pure" MPEG-2 PS file); MEncoder still produced .avi
  with broken AV sync+skipping from this.

  * Opening above .MPG in VideoRedo TVSuite, running it through QuickStream Fix
    into yet another new .MPG; MEncoder still produced .avi with broken AV
    sync+skipping from this.

* Converting my .VOB to MPEG transport stream with ProjectX; MEncoder still
  produced .avi with broken AV sync+skipping from this.

* Demuxing my .VOB to .mpv and .ac3 elementary streams with Womble and remuxing
  those (with Womble again) to a fresh .MPG file.  MEncoder still produced
  .avi with broken AV sync+skipping from this.

* Ran Womble's GOP fixer on .VOB in test mode (its "scan GOP time codes, video
  and audio PTS, and GOP size errors" function) -- no errors reported.

Each new .MPG/.TS file generated by the tasks above, incidentally, also played
without AV sync+skipping problems in VLC and MPC.

Finally:

I tried these three tests (playback tested only in MPlayer for Windows r31027
from http://mulder.at.gg/ since MPC/VLC didn't like the AVI wrapper for MPEG):

* Stream copy both:
  mencoder.exe input.vob -oac copy -ovc copy -o output1.avi
  Result: output1.avi A/V sync NOT broken+no audible skipping.

* Encode video, stream copy audio:
  mencoder.exe input.vob -ofps 29.97 -vf scale=640:480,denoise3d,softskip,harddup -oac copy -ovc x264 -x264encopts bitrate=1200:pass=1 -o nul
  mencoder.exe input.vob -ofps 29.97 -vf scale=640:480,denoise3d,softskip,harddup -oac copy -ovc x264 -x264encopts bitrate=1200:pass=2 -o output2.avi
  Result: output2.avi A/V sync NOT broken+no audible skipping.

* Encode audio, stream copy video:
  mencoder.exe input.vob -af volnorm=1 -oac mp3lame -lameopts abr:br=192 -srate 32000 -ovc copy -o output3.avi
  Result: output3.avi A/V sync BROKEN + audible skipping.

Aha, the AC3.  So I demuxed the VOB using Womble to get at the AC3.  Ran the
demuxed AC3 through http://www.free-codecs.com/download/ac3fix.htm but "No bad
frames encountered" was the result, and doing a binary compare (Windows'
"fc.exe /b infile outfile") of the demuxed AC3 with the new AC3 spit out by
ac3fix found no differences.

The demuxed AC3 also plays fine in MPC, VLC, and MPlayer for Windows r31027
(no audible skipping).

So.  It would seem there is *something* about this video file, quite possibly
its AC3 audio, that MEncoder just cannot handle ... yet which VLC, MPC, MPlayer,
Womble, and AutoGK's backend software can transcode/play just fine.

And that's where I fail to see what to do next.  Besides making a copy of the
VOB available and asking if any uber experts reading this can determine why
MEncoder refuses to generate a synced and non-audio-skipping .avi from it.  :-)

Here:  http://www.megaupload.com/?d=DXFZ65LC

Note that the .VOB is huge (600 MB), so to make this download as inoffensive
as possible, I used Womble to stream-copy just its first 230 MB into a VOB-
free .MPG file.  Don't worry, I checked, and MEncoder's AV desync+skipping
problem isn't altered by doing this.  Whatever problem exists in the original
VOB carries over to the shorter MPG.  So this is only to save downloading
time and shouldn't taint "exhibit A".  Anyway: the "Dreyfus" TV commercial at
the MPG file's end is where the desync problem reveals itself.  Up until then,
the MPG file's video (Amiga computer graphics) has nothing to do with its
audio (instrumental music -- so there, you can only listen for the skipping
issue).  Hence the need to copy at least 230 MB.

Cheers,
SW