Hello, i just join for this tropic :-D.
I have a elecam and it seem to be nearly the same.
To get access to video0 i used lsof | grep video and used kill to terminate the process.
Then i tried your ffmpeg to get a image or video.
./ffmpeg -f v4l2 -channel 0 -video_size 640x480 -i /dev/video0...