Updating to macOS High Sierra (10.13) went smoothly, in all but one regard. Since the upgrade, I’ve not been able to use Facetime calling, or anything else that uses my MacBook Pro’s built in webcam.
Going to System Profiler, it showed under “Camera” → “No video capture devices were found.”
But under USB settings, it showed “FaceTime HD Camera (Built-in)”.
Apple Developer Forums initailly suggested that Parallels was a problem, but it seems the bug affected VirtualBox too.
First I tried updating VirtualBox to version 5.1.28-117968, but even after a reboot, no joy. Using the provided un-install script that thoroughly rids your system of the associated KEXTs (don’t just drag the app to Trash) did do the trick.