if not with iTunes how about Spotify ?
Don't have any idea what that is. If you want your Arduino to trigger something then I suggest you need to investigate what options that something has for being triggered. If your PC is running Microsoft Windows then it's relatively easy to launch applications and send keystrokes from the Arduino. It's up to you to figure out what applications you want to launch and what keystrokes to send it, though.
Outside of Windows you would need to create your own application to do that, but this is still relatively simple to do. Still, knowing what applications and keystrokes and so on you want to invoke is really something you ought to expect to figure out for yourself and has nothing to do with Arduino.