Via my colleague Jonathan Sadowski, a simple command to run in Terminal to fix your Mac’s camera when it’s not working properly.
sudo killall VDCAssistant
Sometimes the video feed is just black or blank — other times you might see an error like “There is no connected camera.”
After you run that command in Terminal, the camera’s process restarts and the camera should work again. No need to reboot the entire computer.
Note: the command requires entering your administrator password.
Update: if you use the Alfred tool on Mac, Nick shared An Alfred workflow to reload the Mac Camera.