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~/.Xmodmap

Xmodmap's keyboard mapping configuration.

gMPlayer example ∞

This works right away for gMPlayer.

! https://wiki.xfce.org/faq
! All possible keysyms can be found in /usr/lib/X11/XKeysymDB or 
! /usr/share/X11/XKeysymDB. To ensure that the .Xmodmap file is loaded 
! when you start Xfce add /usr/bin/xmodmap $HOME/.Xmodmap to your 
! .xinitrc or .xprofile file. When you start the shortcut editor the 
! assigned keysyms should show up when you press one of your multimedia 
! keys. Now it is possible to assign a command to them. 

! Add /usr/bin/xmodmap $HOME/.Xmodmap to your .xinitrc or .xprofile

! Dell multimedia keyboard:
keycode 162 = XF86AudioPlay
keycode 164 = XF86AudioStop
keycode 160 = XF86AudioMute
keycode 144 = XF86AudioPrev
keycode 153 = XF86AudioNext
! Volume control knob
keycode 176 = XF86AudioRaiseVolume
keycode 174 = XF86AudioLowerVolume
! note key
keycode 129 = XF86AudioMedia

! The application keys are:
! 234 233 232 231 178 236 198 161