FWIW, most of the patent war was about how Sonos syncs the volume controls so that changing a master volume level changes all the synced volumes. Seems obvious (and therefore unpatentable) but there is an ever-so-slightly-not-quite-obvious-at-first-glance aspect to it.
I believe Google caved on this and doesn’t allow master level control with their devices. And of course they have been counter suing Sonos on other patents as a result.
It has to do with tracking the levels in the group.
You want to be able to slide a master level up and down and have the levels maintain the "same" balance, even if one of the players ends up going to (effectively) zero level when you have turned it down. Takes a little bit of thinking about how you represent the range of the levels.
I think the patent is actually quite a bit broader, and covers using a UI that has a master volume control across players whose individual volume levels are displayed as well.
Google pulled all "master" level control in response.
I believe Google caved on this and doesn’t allow master level control with their devices. And of course they have been counter suing Sonos on other patents as a result.