I recently faced a situation where I was trying to watch a movie in mplayer in xmonad and it wouldn’t go fullscreen on pressing ‘f’!!
After some reading on the internet I found the solution. And the solution to make ‘f’ work in xmonad is pretty simple. There are two ways to do it:
#1) Add the following line in ~/.mplayer/config file using any text editor:
#2) Fire up a terminal and go in the directory where your video lies(eg. cd Downloads) then type:
mplayer -fstype none filename
Use any of the above steps and voila! ‘f’ will make mplayer go fullscreen again 🙂