Linux – global hotkeys in xfce

I noticed in xfce, global hotkeys don't seem to work. Such as:

• multimedia buttons (play/pause/volum up/down/mute, etc)
• gnome-do not appearing when hitting the specified key (<alt>space in my case).

Is this a feature of xfce that can't be worked around? or is there a way to "fix" it?

PS: for gnome-do I worked around it by binding <alt>space to gnome-do from the keyboard settings page. Xfce Settings Manager > Keyboard > Application shortcuts

Update

To clarify, I already bound the volume up/down/mute to inc/dec/mute volume using aumix and a special script for mute which I found on ubuntu forums.

I noticed that the play/pause button works only when the media player has the focus; it doesn't work as a global hotkey. If I remember correctly, in Gnome, the media players respond to play/pause regardless of where the focus is; so it's either an Xfce issue or some sort of service/daemon is missing.