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At some point in Catalina's evolution (10.15.5+ ?) situations started recurring where there’s no video with the Thunderbolt Display attached and the MacBook Pro in closed clamshell mode when attempting a videoconference via FaceTime or other videoconferencing app (Skype, Zoom, etc). What is strange is that the Display FaceTime HD camera is selected and the green LED is illuminated. I also tried disconnecting the Thunderbolt Display to see whether the MacBook Pro’s built-in FaceTime would transmit live video — and it did. But then there was no audio! I was able to reconnect the Thunderbolt Display to regain audio, but of course there was no live video.

The workaround for this problem is to restart the computer.

Has anyone else seen this problem, and is there a fix besides restarting?

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  • If you weren't having this issue before and it suddenly shows up, then the fix is a restart - it's a bug. First order of business is to leave feedback: apple.com/feedback and I would cross post in both MacBook Pro and macOS categories. When this happens, can you take a look under Sound in system preferences and see where the audio is being routed. Before doing a restart - try switching audio to something else and switching back. See if that has any effect.
    – Allan
    Aug 8 '20 at 21:49
  • I've filed a feedback report. But the most commonly-encountered symptom is no video (at least with the TB display attached). And if it's a bug, then surely it would be experienced by others, yet I can't find any reports on the 'net.
    – odysseus
    Aug 8 '20 at 21:52
  • Before the pandemic started, I was rarely using videoconferencing, so it's possible the problem isn't entirely recent.
    – odysseus
    Aug 8 '20 at 21:58
  • Not too many people have the Thunderbolt display - they we're very expensive for what they were so you're odds of having your configuration and experiencing your issue is very small. Additionally, if experienced by someone else, there's no guarantee they'll post their experience online. They may simply say "This 5+ year old device that's not capable of 4K is bing a PITA...let me go buy a new one."
    – Allan
    Aug 8 '20 at 21:59
  • A bug doesn't necessarily have to be software - I was going off of the fact that you said "some point in Catalina's evolution" meaning it was working then it wasn't - it could be hardware. You could have a flaky Thunderbolt monitor with respect to the HD Cam. It's impossible to know without some diagnostics which is where I started in my initial comment.
    – Allan
    Aug 8 '20 at 22:01
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I know this is an old question, but just in case it helps someone else who lands on this page: it seems this is related to a bug with MacBook Pros after they wake up from sleep. You can deal with it by simply restarting the camera plugin. Close the videoconference app, open Terminal and type:

sudo killall VDCAssistant

Type in your password at the prompt and that's it. If the issue was related to the wake-up-from-sleep bug, then the Thunderbolt Display camera should be working once you start the videoconference app again.

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  • Good suggestion. Do you know where the VDCAssistant is? Apr 24 at 18:15
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    @Darwin /System/Library/Frameworks/CoreMediaIO.framework/Versions/A/Resources/VDC.plugin/Contents/Resources/VDCAssistant
    – grg
    Apr 25 at 7:46
  • @grg Man of honor Apr 25 at 8:46

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