Joel was running Windows 10 (on a Microsoft Surface). The error he got was

Error:

NotReadableError: Could not start video source
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Here's the full email he sent me:

Here's the error I got, and was able to recreate it today.
To recreate:

1.  In a Zoom meeting, start the video (so camera is in use)

2.  Go to Bucket Brigade

3.  Calibrate latency and mic volume

4.  Receive the error, and be unable to do anything else on bucket brigade due to the error page being the only available page.

This error was also encountered by successfully calibrating, turning off video on bucket brigade, starting video on zoom, and then attempting to start video again on bucket brigade.

This was avoided by turning off video in Zoom.  Once it was off, the bucket brigade page would load and I could turn off the video there; once that was off, I could turn the video back on in zoom and use bucket brigade normally - just so long as I didn't turn on video there.

I believe that Lane was experiencing the same issue, but Jim seemed to be able to have video in both Zoom and bucket brigade.  [I was. Though I started the BB video before Zoom  -Jim]

Joel

I was using Chrome, and saw a few of the large white boxes as well a a few normal videos. I don't know what others were using. 

I've got an email in to Joel asking if he remembers what the alert message he got said. As far as I know he was the only person to get such a warning. But it resulted in his video image looking very unusual -- as seen by him and by everyone else. It was in black and white, twice the height of other boxes, and pulsed/flickered. I'm sorry that I didn't think to take a screenshot...

A followup: We tried the server today, with video, with seven people. There were lots of problems where different people weren't shown some other people, just blank white boxes. (Some were close to square, others wide but not high; we suspect the latter were people who had chosen the Don't Show Video option, but the former had opted for video - and in fact could see themselves - but some problem prevented some others from seeing them.) 

One other person got errors saying the video was being used in unsafe ways.

We ended up turning video off and using audio only - which was still quite useful.

And we used zoom to screenshare the PDFs of the sheet music.

I just scheduled a Swarthmore sing for 1:30pm EST this Saturday, and plan to give the video portion a try rather than a concurrent Zoom session.

But I also use zoom's screen-share feature to enable everyone to see the sheet music of whatever we're singing at the moment; can you think of any way for me to duplicate that via your server?