These are my multimedia keys. Maybe can be useful for others.
Go to CompizConfig -> General -> Commands, and add some of these commands:
| What i want | keys | command |
| lock the screen | <Super>l | xscreensaver-command -lock |
| launch audio player | XF86AudioMedia | clementine |
| audio volume down | XF86AudioLowerVolume | amixer -c 0 -- sset Master playback 1- |
| audio volume up | XF86AudioRaiseVolume | amixer -c 0 -- sset Master playback 1+ unmute |
| mute/unmute | XF86AudioMute | amixer -q set Master toggle |
| view the system processes | <Control><Alt>Delete | lxtask |
| Config monitors | <Super>F8 | lxrandr |
| Take a screenshot | Print | screenie |
