When a tab becomes audible (ie. the playing sound icon shows up), register all players on the site.
This ensures dynamically created players that weren't registred by our DOM mutation observer are also handled.

Opened a twitter video, I clicked on it so it started playing with sound, now I can control it. Previously it would not detect it.

Could also cause unintended side-effects if another tab starts playing sound suddenly?

I don't fully understand why neither createElement nor the mutation observer detect it, though.