I got irked the other morning when I wanted to watch his Steveness from San Francisco via the QuickTime stream. So I looked around, and, lo and behold, there is something quite simple that fixes this problem. This Apple KnowledgeBase document explains the problem and solution:
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.Now, I don't know which application would have changed my settings, but the fix is quite simple. You simply open /Applications -> Utilities -> Audio MIDI Setup and change the output settings to 44100.0 Hz (the iMac supports up to 96600 Hz).
An easy fix, but annoying; which applications would be making this change? I'll try and keep my eyes on it, but, since I don't use any audio recording software, I cannot figure out what might be the cause.

