Do you like when you pull out the headphone cable from your iPhone the music stops?
Well, after installing the SmartStop app, your Mac will do it to.
Moreover, if you wish, SmartStop can automatically start the music, whenever you plug-in your headphone or speaker. NOTE: The SmartStop can only be downloaded via the Mac App Store (the buy link redirects you to its App Store page). To purchase/download applications via the App Store an Apple account is required.
