Media Session Callbacks

一旦是视频app在同一个activity中运行媒体会话和媒体控制器，媒体会话回调的实现与音频应用server/client 架构实现的回调不同。由于没有服务的调用，所以notification都是由NotificationManager来控制的。下面的列表展示两种回调函数中不同的控制方式。

_onPlay()onPause()onStop()Audio FocusrequestFocus() passing in your OnAudioFocusChangeListener. Always call requestFocus() first, proceed only if focus is granted.abandonAudioFocus()Media SessionsetActive(true) - Update metadata and state-Update metadata and statesetActive(false) - Update metadata and statePlayer ImplementationStart the playerPause the playerStop the playerBecoming NoisyRegister your BroadcastReceiverUnregister your BroadcastReceiverNotificationsShow notificationUpdate notificationCancel notification