So, I resynchronized audio with a time shift of 2000ms in avidemux 2.5.4.
However, whatever I try, after saving (I tried avi, mp4, mkv) the new file is out of sync, like the original.
Any clue?
2.5.4 is something like 5 years old
Hmmm... looks like the ubuntu repository needs work...
Anyways, I upgraded to 2.6.10 and found that the 2000ms audio shift from the old version makes no sense in the new version: now the correct shift is 200ms. Saving as mkv works, saving as avi loses the shift.
Anyways, thanks for helping me out!
When I was using old versions, I needed to press the audio shift arrows for Avidemux to take it into account.