At the moment we have a lot of video conferences at school. We should always go in with a micro and a picture. (Via the HPi school cloud (Big Blue Button)). Strangely enough, my camera has been going crazy lately. I'm in with the laptop. When I want to turn on the camera there's always a change for 2 seconds you see me for 2 seconds you see black and then it just needs to be turned off. When I try using the camera app on my laptop the exact same thing happens.
I can't tell you exactly what it could be because of, I don't know your system.
However, if you use Windows 10 on your laptop, I recommend using a magnifying glass to look for data protection settings in the system. There you have to check whether your camera is approved for this app. If not then just set to allow. The same goes for the microphone.
Most of the time, this setting leads to such problems, if everything necessary is allowed in the data protection settings of Windows 10, it can be due to many other things, e.g. The driver of the camera etc. But making assumptions here is just like picking up the crystal ball.
