I tried to activate GNOME Multimedia Keys on Exaile and I got the error the following error:
org.freedesktop.DBus.Error.UnknownMethod: Method "GrabMediaPlayerKeys" with signature "si" on interface "org.mate.SettingsDaemon.MediaKeys" doesn't exist
What worked for me was to go to
Plugins, in the list find
Hotkeys -> Xkeys and click on the checkbox to enable it.
If you get the following error message:
mmkeys.so is not available
sudo apt-get install python-mmkeys
Now you should be able to tick the checkbox and your multimedia keys should work.