I can't encode the audio of a QT movie to .ac3 ! I've chosed the option of the presets and started the encoding. The following message is posted:

Encoding started on Sat Jul 17 23:27:26 CEST 2004
Input #0, mov,mp4,m4a,3gp, from '/Volumes/Macintosh HD V/movie.mov':
Duration: 01:54:48.5, bitrate: 49576 kb/s
Stream #0.0: Video: mpeg4
Stream #0.1: Audio: pcm_s16be, 48000 Hz, stereo, 1536 kb/s
Output #0, ac3, to '/Volumes/Macintosh HD V/movie.ac3':
Stream #0.0: Audio: ac3, 48000 Hz, stereo, 192 kb/s
Stream mapping:
Stream #0.1 -> #0.0

No file was created. What am i doing wrong?