[FFmpeg-user] Concatenate videos with alternate audio

[Giampaolo Rodola']

Hi,
I have some mp4 files I'm trying to stitch together.
Some of them have audio and some don't as in:

1.mp4 (has audio)
2.mp4 (has audio)
3.mp4
4.mp4
5.mp4 (has audio)
6.mp4 (has audio)

I'm using MP4Box to stitch them together, like this:

MP4Box -v -add 0.mp4 -cat 1.mp4 -cat 2.mp4 -cat 3.mp4 -cat 4.mp4 -cat
5.mp4 -cat 6.mp4 -new intermediate.mp4

That works fine for the video but the whole audio track gets appended
*at the beginning* of the new file.
Basically the audio of 5.mp4 and 6.mp4 gets shifted to 3.mp4 and
4.mp4, and I have silence at the end of the video.

I posted on MP4Box mailing list, but it seems MP4Box can't do anything
about this:
http://sourceforge.net/projects/gpac/forums/forum/287547/topic/5801129

What about ffmpeg?


Thanks in advance,

- Giampaolo