Mac上遇到"There is no connected camera"

上周打开FaceTime，发现摄像头用不了，出现“ There is no connected camera”的提示。
网上查了下，没怎么细看，直接咨询了Apple服务，顺利解决。下面是对话截图和具体步骤：

对话截图

1. Shut down your Mac.
2. Found Command(⌘), Option, P, and R on your keyboard.
3. Turn on your Mac.
4. Press and hold the Command-Option-P-R keys immediately after you turn on your Mac.
5. Hold these keys down for at least 20 seconds to ensure that your Mac completes the process correctly.
6. Release the keys.