When I maximize mplayer, the parts of the screen not covered by the video itself show "redraw" garbage from whatever was under the window before.
See attached screenshot. mplayer should probably at least black out the parts of its window that aren't being used.
I would also note that normally mplayer dynamically resizes itself to preserve aspect ratio if you attempt to resize it...but:
a) I don't think it should be attempting to do so (violation of window manager principles in the X11R6 developer manual)
b) If the window manager (openbox in this case) force-sizes the window (such as maximizing it), mplayer winds up leaving garbage in the unused parts of its window.
I'd much rather mplayer properly black-fill things, and it wouldn't hurt IMHO if it didn't try to force-size itself. VLC does it right by fitting its video playback inside the window and black-filling any unused parts of the window.
Created attachment 445630 [details]
Created attachment 445632 [details]