This fixed the issue. Found in Apple Knowledge Base:
No sound from some applications, but system alert sounds play (Mac OS X
10.3, 10.4)
Some audio applications may change your computer's audio settings to a
sample rate that is too high for other applications to use. In this
situation, system alert sounds still work, and does iTunes, but other
applications may have no sound (audio output). This document applies to
Mac OS X 10.3 or later and applications that use QuickTime 6 for audio,
such as Safari and Quicktime Player.
This can happen on Macs that support high sample rates (higher than
48000 Hz):
* iMac G5
* Mac mini
* Power Mac G5 models that support sample rates higher than 48000
Hz
* PowerBook G4 support sample rates higher than 48000 Hz
For example, if you play an Internet movie in Safari, it will make no
sound; if you open a QuickTime movie on your computer, QuickTime Player
reports the following error (and the movie will have no audio):
"You may experience problems playing a sound track in (Movie Name).mov
because a software component needed by the movie could not be opened."
Solution
1. Open Audio MIDI Setup (/Applications/Utilities/), then check the
Audio Output setting.
2. Change the Audio Output setting to 44100.0 Hz.
3. Quit Audio MIDI Setup.
Why does this happen?
Some third-party audio applications may change your computer's audio
output setting. In fact, if you use the third-party application again
after applying the above solution, the issue might occur again. Observe
changes by watching the settings in Audio MIDI Setup before and after
running a third-party application you suspect might be causing the
issue. Contact the manufacturer of the application for more information.
