Google is expanding its Google Now functionality by the minute. It is not only competing with different kind of services from Apple and others, but also is integrating it with the just unveiled Android L, Android Auto and Android Wear platforms. Google is now working on integrating media control features via voice commands.
The feature should be a part of a minor Android update, which should come later. It currently works on some phones and not on others. But the way this works is pretty great still. You can restart the current song by saying ‘previous songs’ (It wouldn’t play the actual ‘previous song’). Other than that, ‘Play next song’, ‘next song/track’, stop music, pause music will work just the way they are intended to. The volume settings button needs wk though.
Google is working on its media functionality, which is one arena it has never been able to do better than Apple in. Apple still reigns in that arena with its iTunes functionality.
Keep checking your phone to see if you have got the update.