Sorry for that one. MPlayer has a cropdetect option which gives you information about width and height etc for use with -vf crop. So what you have to do normaly is to run mplayer with cropdetect find a suitable crop-line and rerun mplayer with this line in -vf crop.
What the script here does, is just that, but automated. So you only have to run mplyarcrop.pl you_movie.avi
I use it on every second movie I play, so I thought it might be usefull for someone else. First piece of code I post here.