shinobar investigated a similar problem with ffconvert and found that by replacing the contents of /usr/share/ffmpeg with the files from another ffmpeg package, ffconvert worked:
I have applied shinobar's fix to ffmpeg and uploaded the fixed package (2.5MB):
If you need the 'dev' package (2.6MB):
Comments:Posted on 20 Jan 2012, 12:32 by shinobar
ffconvert and ffmpeg version
Recently i discovered that the problem was a version issue.
The problem occurs at ffconvert-1.0 with recent version(0.7 and newer?) of ffmpeg. That is why reverting the files in /usr/share/ffmpeg solves the problem.
FFconvert-1.2 is now ffmpeg version free: