Nice piece of work there =D Much appreciated. I also ran into a couple of the same problems others have had here but managed to sort them. The first was the Screensaver menu entry which was sorted thanks to theonlytruth and brendanpiater. The second was that, like others, fullscreen preview didn't show nor did it kick in when it should have and only "seemed" to go back to desktop after first showing a black screen.
This last issue was fixed by adding a specific output option in the code, I chose xv and that works like a charm :
You can of course choose whichever output you wish whether it be xv, x11, gl, gl2 etc
## setup MPlayer aruments, remove -nosound if you want the video
## to play sound. If you have to specify the video driver to use
## then add that to the list
MPLAYERARGS="-nosound -nolirc -vo xv -wid $XSCREENSAVER_WINDOW -nostop-xscreensaver -fs -really-quiet"
## path to video
exec mplayer $MPLAYERARGS -loop 0 "$VIDEO"