This extension continually monitors all chrome windows to mute all inactive tabs and unmute active tabs.
(2018-03-29) Hoai Ly: Is was what I was looking for but it only worked half the time. all the other extensions that I've found only muted the inactive tab if the active tab made sound. This extension looked like it muted the inactive tab regardless if the active tab had audio but it only worked half the time. Shame.