[MEncoder-users] mencoder concatenation warps audio out of sync

[mencoder at perlmeister.com]

On Fri, 6 Nov 2009, Reimar Döffinger wrote:

> Probably copying sample_size*channels*sample_rate*desired_duration
> bytes from /dev/null and using the -rawaudio stuff.  ...  First step
> as above and use -audiofile -audio-demuxer rawaudio -rawaudio ....

Unfortunately, that doesn't work either:

With sample_size=1, channels=1, sample_rate=8000, duration=2s, here's
a file with 16,000 zero bytes, silence.dat:

     dd if=/dev/zero of=silence.dat bs=1 count=16000

With your suggestion, let's add the silence to the JPEG movie:

     mencoder 'mf:///tmp/*.jpg' -mf fps=30 -o titleraw.avi \
       -audiofile silence.dat -audio-demuxer rawaudio -rawaudio \
       channels=1:rate=8000:samplesize=1:bitrate=64:format=0x0000 -oac \
       copy -ovc lavc -lavcopts vcodec=mjpeg:vbitrate=1000

Out comes titleraw.avi with

     AUDIO: 8000 Hz, 1 ch, u8, 64.0 kbit/100.00% (ratio: 8000->8000)
     VIDEO:  [MJPG]  160x120  24bpp  30.000 fps  349.9 kbps (42.7 kbyte/s)

and it plays approximately 2 secs both with and without -novideo. 
But if you listen in on

     http://perlmeister.com/tmp/titleraw.avi

you can hear two loud cracks at the beginning and at the end.

And what's worse is that mencoder now refuses to concatenate the 
two videos:

     mencoder titleraw.avi soundtest.avi -ovc copy -oac copy -o outraw.avi

     All files must have identical audio codec and format for -oac copy.
     Exiting ...

and if I force a reencoding of both audio and video with

     mencoder titleraw.avi soundtest.avi -ovc lavc -lavcopts \
        vcodec=mjpeg:vbitrate=1000 -oac mp3lame -o outraw.avi

you can hear at

     http://perlmeister.com/tmp/outraw.avi

that the sound syncronisation in the 2nd part is way off on the 2nd
click and you get a bunch of "Cannot sync MAD frame" errors at the end.

-- Mike

Mike Schilli