Flash video and no sound on OSX at fredericiana:
"Every once in a while though, on Mac OS X it can happen that these Flash video players don’t have sound anymore.
1. open /Applications/Utilities/Audio MIDI Setup
2. check the properties for Built In Output.
3. It might be set to 96KHz. Change it to 44KHz and audio in Flash will return immediately."
(The same might apply to audio input)