How do I change the default configuration of MPlayer movie player?

[Steven Vollom]

I don't know if this is possible, however, since the purchase of my new 
monitor, I find myself always choosing MPlayer as my movie player, because I 
can change to aspect ratio to 16:9.  My preference would be that whenever I 
wanted to play a movie on the computer, it would automatically open with 
MPlayer as the default movie player, and the default aspect ratio to be 16:9.

I also think it would be attractive for people with different aspect ratios to 
be able to set their default settings to meet the needs of their particular 
monitor shapes.  Can this be done?  TIA.

Steven