I have an app that plays an song displaying its lyrics on the screen.
There are different
Services for different use cases. For a
Media Player it depends if you want to have the playback continuously playing in the back- or foreground.
So both cases are applicable for a
Media Player Service. But the Android Developer Guide Media Player Service outshines my answer
Using a Service with MediaPlayer
If you want your media to play in the background even when your application is not onscreen—that is, you want it to continue playing while the user is interacting with other applications—then you must start a Service and control the MediaPlayer instance from there. You should be careful about this setup, because the user and the system have expectations about how an application running a background service should interact with the rest of the system. If your application does not fulfil those expectations, the user may have a bad experience. This section describes the main issues that you should be aware of and offers suggestions about how to approach them