The following command tells the available commands for keyboard input. mplayer -input cmdlist The keyboard shortcuts to mplayer are stored in two locations - /etc/mplayer/input.conf and ~/.mplayer I prefer editing the /etc/mplayer/input.conf. Assign shortcuts to aspect aspect ratio switching as follows switch_ratio e.g. a switch_ratio 1.3333 # 4:3 s switch_ratio 0 # switches back to original aspect ratio b switch_ratio 1.7777 # 16:9 ratio put his at the end of /etc/mplayer/input.conf.