macOS Determinate if Firefox is running a video

So I have to explain little of the context: When coreaudiod is engaged (macOS deamon), the ext. display doesn't go to sleep mode. This wouldn't be a big issue but the problem is... when I switch off the display and, lets say one hour later I start the display again, it doesn't get recognized and says "No signal". Even if no video is running in Firefox, coreaudiod stays engaged sometimes. It's intermittent. If I can determinate that Firefox is not running a video and coreaudiod is engaged a script can send a

-9

signal to Firefox. If a video is running of course not because I'm watching a video. But how can I find out Firefox is running a video by CLI or Apple-script?