Well, I found out I have a damaged mkv file, a movie encoded with handbrake.
I don't know if it has always been the case. Using vlc to play the movie, it stops altogether after 1 hour 20, but it's possible to play back the movie after 1 hour 23. And using Western digital DLG didn't help, no bad cluster was found on the hdd.
So I was wondering if there was some software that could examine corrupt movies.