Drag another window over the top. You can't just play more audio over the top as it just makes a mess, so it needs mute.
One issue is that you're consuming unnecessary bandwidth. Another is consuming unnecesary CPU. so that solution just give a different perception but don't solve these two issues.
sure, but it seems like a rare enough need that its questionable whether its worth cluttering up the interface and adding to the code base to implement it.
We need mute for sound because we, humans, can not "close our ears" or "listen away". The need for "video mute" is not as strong. We have the feature built-in.