Comment 17 for bug 857243

It works for me with the following deskop file in ~/.local/share/applications/mplayer.desktop

[Desktop Entry]
Name=MPlayer
GenericName=Media player
Exec=mplayer %U
TryExec=mplayer
Icon=mplayer
Type=Application
Categories=AudioVideo;Player;
NoDisplay=true

I've created the icons with:

$ cd ~
$ wget http://upload.wikimedia.org/wikipedia/commons/8/81/MPlayer.svg
$ cd /usr/share/icons/hicolor
$ for i in *x*; do sudo convert -background none ~/Mplayer.svg -resize $i $i/apps/mplayer.png; done
$ sudo gtk-update-icon-cache -q -t -f /usr/share/icons/hicolor