The mpv video player on Android from the f-droid repository has vertical
swipe at the right side of the screen to control volume and vertical swipe
at the left side of the screen to control brightness.  It isn't the first
program to do that (I've seen it in other Android players) and it appears
to be a common method of control.

Due to this being common and being used by a popular FOSS video player I
think this would be a good feature to add to livi to increase usability.