ffmpeg -i in.avi -vcodec mpeg2video -r 25 -s pal -vb 2048 out.mpg
ffmpeg blamed about not being able to encode to mpeg2video.
ffmpeg -formats | grep mpeg2video
D VSDT mpeg2videoas result, where the E is missing which would indicate the encoding support.
Don't know when exactly this support got lost (ffmpeg also disappeared from Medibuntu repository), but after some investigation I found the solution.
You have to install different packages which include this video codec.
You need to have the multiverse repository enabled (see this post about how to do this from the command line).
sudo aptitude install ~nlibav.+-unstripped.+
If you already have installed the stripped packages, you'll be asked to remove them as they are in conflict with the unstripped one.
Now, the previous instructions give this output
DEVSDT mpeg2videoand encoding to MPEG-2 works fine.