[MEncoder-users] Dies on completion of 2nd pass, no output file

[Rich Felker]

On Sat, Oct 15, 2005 at 03:35:55PM -0500, Pete Davis wrote:
> > >
> > > Pos:7229.7s 180776f (100%)  35fps Trem:   0min 1147mb  A-V:0.083
> > [1000:319]
> > > Skipping frame!
> > > mencoder: ratecontrol.c:644: ff_rate_estimate_qscale: Assertion
> > > `picture_number<rcc->num
> > > _entries' failed.
> > >
> > >
> > >
> > >
> > > My command is:
> > >
> > > mencoder -of avi -sws 2 -vf scale=512:288 -ovc lavc \
> > > -lavcopts vcodec=mpeg4:vme=4:mbd=1:vbitrate=1000:trell:vhq:vpass=1 \
> > > -oac copy input.vob  -loadidx  -o /dev/null
> > >
> > >
> > > mencoder -of avi -sws 2 -vf scale=512:288 -ovc lavc -lavcopts \
> > > vcodec=mpeg4:vme=4:mbd=1:vbitrate=1000:trell:vhq:vpass=2 \
> > > input.vob  -loadidx -o output.avi -oac \
> > > mp3lame -lameopts mode=3:vbr=0:br=80:ratio=1
> > 
> > Does -oac copy look the same as -oac mp3lame -lameopts
> > mode=3:vbr=0:br=80:ratio=1 to you? :)
> > 
> > Rich
> > 
> 
> While that's certainly something to check, there's not necessarily anything
> wrong with that.

There's definitely something wrong with it unless you use -mc 0.
Without -mc 0, different frames (and possibly a different total number
of frames, thus the crash) will be encoded on the two passed. In
either case the stats from the first pass won't match with the second.
Sometimes this isn't a big problem, but it will move keyframes at
scenechanges to be one frame away from the scene change in some cases,
resulting in incorrect bitrate and/or significantly reduced quality at
that scene change.

> In fact, I've done at least 400 encodings of various types
> of source material with -oac copy on the first pass and -oac mp3lame on the
> second.

You got lucky.

If you want to avoid encoding audio twice, do three passed:

1: -lavcopts vpass=1 -oac copy -o /dev/null dvd://1
2: -lavcopts vpass=2 -oac copy -o foo.avi dvd://1
3: -mc 0 -noskip -ovc copy -oac mp3lame -o bar.avi foo.avi

This will also prevent the a/v desync bugs in mencoder's lame support
from messing up your movie.

Rich