Comment 41 for bug 1302885

No one ever answered my question (#32):

How does unity work around gnome-settings-daemon dropping support for media keys?

There does appear to be code in unity-settings-daemon for this:
http://bazaar.launchpad.net/~unity-settings-daemon-team/unity-settings-daemon/trunk/files/head:/plugins/media-keys/

I cannot verify that code is functional as I am unwilling to install Unity.

>cs-gon
You can probably get away with installing the Saucy version of the package (download it from the lauchpad page, install with dpkg or gdebi); but I can't gurantee it will solve the problem permanently.

https://launchpad.net/~zorin-os/+archive/ubuntu/packages/+sourcepub/3778150/+listing-archive-extra