The buttons are not labeled but follow the typical convention where the outer buttons function as volume up and down and the middle button engages play / pause. (pooraudiophile.com)
You can find this in the camera settings by swiping to the left and scrolling down to the Volume button function option. (androidcentral.com)
14 action buttons + 1 directional pad with push button function. (shop.thrustmaster.com)