This is an interesting idea,
dwmcqueen.. To me, it sure looks like a job for
doityourself (see the
desklets
page) and a little scripting, not for a whole, separate
desklet.
The only special point concerns how to "embed" mplayer
windows inside the desktop: have a look at the
-rootwin option from mplayer -- you
might have to play around with the video output as well (I
did)... See:
Otherwise, if you use a window manager with a fake root
window, you also have a
-wid
mplayer switch that you can use in conjunction with the
ADESKLETS_ROOT environment
variable to specify the desktop window. Finally, you could
also achieve the same effect with a little help from your
window manager (look around in the doc for decoration-less
windows), or ultimately from third party applications such as
Devil's
pie. Have fun!