In mobile clients, to pause playback, you must first tap the screen to bring up the GUI, then locate and tap the pause button. When you want to pause, you may need to pause quickly, so the additional delay of waiting for the GUI to appear sucks.
In iOS, a double-tap is mapped to the zoom function. I would argue that play/pause is used more often than zoom and we’re wasting the choice double-tap input on a little-used function. Anyway on iOS pinch out/in makes more sense for zoom, right?
So, I propose making a double tap on the screen a play/pause toggle for all clients, as a shortcut to the current method of tap, wait, move finger, tap. Move zoom into the playback settings, and/or give it a more appropriate shortcut gesture.