I discovered last time, that Play / Pause / Next / Prev buttons from keyboard doesn’t work on my MacBook and OS X. Normally, the click of play button opens the iTunes or play/pause songs. It suddenly stopped working and I didn’t know why. The issue was Google Play Music – extension for Google Chrome browser to use service with the same name, upload music etc.
The simplest solution is to remove that extension from Google Chrome. You can do that by use hamurger menu (three dots on right-top), select More Tools and then Extensions. On new page just click trash icon on Google Play Music extension. But what when you want use both iTunes on GPM? You must change keyboard shoutcuts for that extension.
You can do this on the same extensions list page. Just click “Keyboard shortcuts” link on bottom. Chrome will open popup with configuration table, where you can change shourtcuts for all extensions. Default Google Play Music shoutcuts overwrite system settings, after change everything will be ok.