Apple has changed something that interferes with some applications/drivers using the webcam, mirroring the screen (Airplay and Airplay-like) and providing USB graphic cards.
Uninstalling those (make sure to use Google to find what kernel extension they installed), make sure the system rebuilds the kext cache by running
sudo touch /System/Library/Extensions
and restarting solves the problem for most people posting to that list.
List of applications I found that might cause the problem, mostly out of a lengthy thread in the Apple support forum:
- Air Display
- DisplayLink Driver
- Splashtop virtual display driver
Not all of this must be affected, and some are actually debated in the thread (like Parallels and VMWare). They might just do the
touch mentioned above which some users probably didn't do.
Sadly this all didn't help me, so I decided to give up the camera until Apple fixed this and disabled the
VDCAssistant (must be repeated after each boot, when the problem still occurs, and whenever something wanted to access the webcam). Has the advantage over deleting/renaming that you don't have to remind yourself undoing that if it finally is fixed; but you realize very well if the problem still persists after a reboot...
sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.cmio.VDCAssistant.plist