QuickTime Player.app New Movie Recording Error: won't record
Solution 1:
I don't know why this was a problem in the first place, but I was able to resolve the issue from the Activity Monitor so that QuickTime can now access my FaceTime HD Camera:
launch Activity Monitor
select Activity Monitor >> View::All Processes
select the process "VDCAssistant" (owned by root)
select Activity Monitor >> View::Quit Process
(also: Option+Cmd+q)
The same can be done from the command line with killall:sudo killall VDCAssistant
...and here's a more complete listing of things to try if the FaceTime camera has gone wonky.