If I change volume using the up and down keys or the volume slider, the controls become visible and then disappear after a short time. However, if I change volume using just the mouse scroll wheel, and am careful not to move the mouse pointer, the controls remain visible forever. This is because the mouse scroll wheel does not start the visibility timer.
This viability timer is started by the mouse move, the space bar and maybe other events, but not the scroll wheel, as it should be. .

Pass this on to the video player programmer. Cheers