I tend to use several music/media players, such as shell-fm, moc and Clementine. And I often try out new ones. In order to be able to use the media buttons on my keyboard for pausing/skipping, I wrote this player_do Python script to automatically route the commands to the right one.
sudo easy_install playerdo
Or, if you prefer this way like me, and have $HOME/.local/bin on your $PATH:
easy_install --prefix=$HOME/.local playerdo
Then use your window manager/desktop to setup keyboard shortcuts to player_do playpause, player_do next etc.
mpris-remote does a similar job, but only for MPRIS players, and I needed others. My script also has an MPRIS backend, so it will support XMMS2, Amarok, Clementine, Exaile, Dragon Player and various others out of the box. It also has support for shell-fm, moc, and rhythmbox.
If you have more than one running at a time, it tries to be intelligent about which one to talk to, although of course it is not always possible to read your mind correctly!
For other players that don't support MPRIS it should be quite easy to add a backend — please fork the bitbucket repository, have a look at the existing backends and send me your patches!