Initially, after updating to OS X 10.9.2, all seemed fine with my 2009 Mac Pro. Then I launched Skype. The application could no longer detect the camera built into my 24-inch Cinema Display. I quickly confirmed that this failure was not specific to Skype. It extended to all programs that accessed the camera — notably Apple's FaceTime and Photo Booth. For example, shortly after launching Photo Booth, a message appeared that said "There is no connected camera."
A Safe Boot points the way
The symptom was not limited just to my account; the camera remained MIA even when logged into a separate account that had no login items. Recommended all-purpose fixes — such as restarting the Mac, resetting the SMC (System Management Controller), or repairing disk permissions — had no effect. I even re-installed OS X 10.9.2 via the combo update but to no avail.
I was able to determine that the symptom did not extend beyond my Mac Pro. The cameras in my MacBook Pro and my wife's iMac continued to work just fine after installing the 10.9.2 update.
One thing did succeed in bringing the Cinema Display's camera back to life: a Safe Boot. It was only a temporary respite, however. After restarting normally, the camera vanished again. Still, this pretty much ruled out a hardware failure as the cause of the problem. Rather, the evidence suggested that the culprit was a file (or files) either in the Mac Pro's /Library or /System/Library folders. Unfortunately, a Safe Boot offers no way to determine precisely what those files might be. As a start in this search, I temporarily disabled the contents of various startup-related folders in the /Library folder: Extensions, LaunchDaemons, LaunchAgents, Preferences and StartupItems. It proved fruitless.
Perhaps OS X's Console logs could identify the culprit file? Nope. If anything, checking the logs only succeeded in raising my anxiety. It revealed that a process called VDCAssistant was crashing at a rate of about ten times a second! I located this OS X file buried in /System/Library/Frameworks/CoreMediaIO.framework/Versions/A/Resources/VDC.plugin/Contents/Resources.
I figured that, while this VDCAssistant file was likely involved in the missing camera mystery, it was not the root cause. This meant that killing the process might stop the crashes but would not bring back the camera. Still, I attempted the kill. Surprisingly, neither the killall command in Terminal nor a Force Quit from Activity Monitor could terminate the process. At this point, I searched the web and found a report that claimed deleting com.apple.cmio.VDCAssistant.plist from /System/Library/LaunchDaemons would stop the crashing but (as I expected) not restore the camera. I never bothered to try this.
AirParrot, AirPlay mirroring, and the missing camera solution
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