This extension pauses Google Play Music when playing audio or video in another tab. Try shortcuts: Cmd+Shift+(8/9/0).
If you are a regular Google Play listener, and wish that you could temporarily pause music while you listen to music or watch a video in another tab, this is the extension you want. While Play Music is playing, if you start watching a video or play any other audio in another chrome tab, this extension will automatically pause Play Music, and once the other tab stops making sound, it will restart the playback.
There are also 3 universal keyboard shortcuts (meaning they will work even if Chrome is not in focus, you can use while doing anything on your computer), Cmd+Shift+ (8/9/0) - give these a try to see what they do. (Ctrl for windows and linux.)