I've updated my tool:

http://jonny.leffe.dnsalias.com

Changes:
- Added "Avi open", should be more compatible with avi input (use the generic open if this fails)
- "Add borders" is now the default method if the input aspect ratio is ~2.35
- FFMPEG's error logging (now you can see the exact FFMPEG's output after obtaining an "Exitcode" error)
- Added volume setting
- Added a check to see if AviSynth is installed
- Installer, with AviSynth and ffdshow included
- Maybe other things i don't remember :P