The other day I found myself with about 200 tabs in 5 windows opened. Travel searches (flights, visas, etc), development, questions, and some entertainment.
Then suddenly some music starts playing on my computer. Where is it coming from? Who knows‽ I had to go on a big hunt.
Since I rarely want the non-focused tab to be emitting any sounds whatsoever, I really think a default:mute policy would make a lot of sense here.
Or at least, some visual indication of which tab is emitting sounds, maybe by replacing the favicon.