Both iOS and Android offer the option to display tools on the lock
screen. This is seen most often in music apps, but not exclusively. If
your application is running in the background and users may need
quick access to pause, stop, or adjust it, consider designing tools for
the lock screen.
The controls do not need to be limited to playing and pausing audio
and video. Any.do for Android uses a widget to prompt app usage first
thing in the morning, and also to help with tasks during the day.