I have been using video files with videoconferences for quite some time now and recently I also put it into a push-to-talk script. Only with Jitsi Meet it never worked – no matter which browser I tried – none could access my “webcam”. Today, after another naive search, I came across this github issue with the solution for Chrome.
You have to set the flag exclusive_caps to 1 when loading the module.
sudo modprobe v4l2loopback exclusive_caps=1
Now the “webcam” works in Chrome \o/
Still not in Firefox – at least in Chrome