That RF remote control comes with a USB dongle; it appears as a HID device so essentially the buttons act as if they are keypresses on a keyboard (cursor keys,

That RF remote control comes with a USB dongle; it appears as a HID device so essentially the buttons act as if they are keypresses on a keyboard (cursor keys, enter etc). So the code just receives the keypresses, and uses them to select the appropriate mpd function (forward/back, volume up/down while the power button simply acts as pause/unpause).