Video Mirror
Hi All,
You'll probably find that you have some video mirroring app installed - AirDisplay, AirParrot or something like that. It's an Apple issue which the other video people say will be fixed (hopefully) in 10.9.3! For now if you need your cameras to work - uninstall the other app(s) and restart.
You may need to launch Skype to get it all going again!
Hope this helps...