Comment 4 for bug 528742

I don't understand very well what happens, but this seems to work: just downgrade ffmpeg to 4:05 (i had the 5:05 version trough the http://ppa.launchpad.net/matthaeus123/mrw-gimp-svn/ubuntu PPA, now i disabled it).
I still have the libavcodec-extra-52 installed (v. 4:05, needed by ffmpeg), but removed libavcodec52 (which conflict with ffmpeg).