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

[mencoder at perlmeister.com]

On Wed, 4 Nov 2009, mencoder at perlmeister.com wrote:

> I have two videos, title.avi and soundtest.avi, which I'd like to
> concatenate using mencoder. However, the audio gets out of sync with the
> video in the process, and this happens both by copying or recoding it.

Hmm, it's been a while ... does anyone know the answer to this one? Is
this the correct mailing list?

-- Mike

Mike Schilli

> I'd be happy for any advice you can give.
>
> You can two small test videos (<1M in size) at
>
>    http://perlmeister.com/tmp/soundtest.avi
>    http://perlmeister.com/tmp/title.avi
>
> to verify what I'm seeing below. Playing soundtest.avi, you can see that
> audio and video are perfectly in sync. Both videos have the same
> video/audio properties:
>
> title.avi:
> VIDEO:  [MJPG]  160x120  24bpp  30.000 fps  349.9 kbps (42.7 kbyte/s)
> AUDIO: 8000 Hz, 1 ch, u8, 64.0 kbit/100.00% (ratio: 8000->8000)
>
> soundtest.avi:
> VIDEO:  [MJPG]  160x120  24bpp  30.000 fps  1187.5 kbps (145.0 kbyte/s)
> AUDIO: 8000 Hz, 1 ch, u8, 64.0 kbit/100.00% (ratio: 8000->8000)
>
> Only difference is the bitrate, as title.avi was created by lumping
> together a bunch of jpegs and soundtest.avi was taken with a video
> camera.
>
> When concatenating the two videos via
>
>    mencoder title.avi soundtest.avi -oac copy -ovc copy -o concat.avi
>
> you get the result available at
>
>    http://perlmeister.com/tmp/concat.avi
>
> for your convenience, and you'll notice that the first audio click is
> out of sync with the video and comes about .5 seconds too late. On the
> following clicks, however, the audio recovers and gets back in sync with
> the video.
>
> It gets worse if the audio of both tracks is re-coded as mp3 via
>
>     mencoder title.avi soundtest.avi -oac mp3lame \
>              -ovc copy -o concatmp3.avi
>
> (only visible with a longer video posted at
>
>    http://perlmeister.com/tmp/concatmp3.avi
>
> with is 44M in length), because audio falls back more and more over
> time.
>
> Any chance to better sync audio and video with mencoder? Thanks for any
> help.
>
> -- Mike
>
> Mike Schilli