I have discovered a bug when using TOGETHER the expand and scale filters.
(tested with 1.0pre5 and CVS)
Try this:
mplayer -vf expand=1000:0,scale=720:576 dvd://1
or (with a different pirotecnic effect)
mplayer -vf expand=0:800,scale=720:576 dvd://1
Is this bug already known?
Giacomo