No audio from Quicktime videos

I have a MacBook Pro running 10.4.6 and Quicktime 7.1.3. When I play QT videos there is no sound, however iTunes and system sounds work fine. I checked Audio MIDI Setup as suggested in another post, and the Audio Output section says "Output is not supported". The Sound widget from System Preferences shows it's using the Built-in output, and as mentioned above, iTunes and others play just fine. Any ideas why Audio MIDI Setup says no output?