[MPlayer-users] Automatically crop to match display aspect ratio?

[Darxus at ChaosReigns.com]

How do I get mplayer to automatically crop to match the aspect ratio of the
video to that of my display?  The panscan option seems likely, but doesn't
appear to do anything (with -vo gl / gl2)  when my display (1600x1200)
is wider than my video (1280x1280)?  The crop option works, but is quite
a lot less automatic.