SourceId
Unique identifier for a media source.
Since an app could offer multiple services, a SourceId is composed of:
packageName: the package name of the application offering a browsing tree
className: the exposed Android MediaBrowserServiceCompat class
This class is open
to allow pre-defining source IDs as objects. For example: object MySourceId("com.test", "com.test.service.MySourceService"): SourceId