Media sessions provide a universal way of interacting with an audio or video player. By informing Android that media is playing in an app, playback controls can be delegated to the app. Integrating with the media session allows an app to advertise media playback externally and to receive playback commands from external sources. These sources can be physical buttons (such as the play button on a headset or TV remote control) or indirect commands (such as instructing "pause" to Google Assistant). The media session then delegates these commands to the app that applies them to the media player for which it is transparent where the commands originated.
A media session lives alongside the player that it manages. You should create
and initialize a media session in the onCreate()
method of the activity or
service that owns the media session and its associated player.
Initialize the media session
A newly-created media session has no capabilities. You must initialize the session by performing these steps:
- Set flags so that the media session can receive callbacks from media controllers and media buttons.
- Create and initialize an instance of
PlaybackStateCompat
and assign it to the session. The playback state changes throughout the session, so we recommend caching thePlaybackStateCompat.Builder
for reuse. - Create an instance of
MediaSessionCompat.Callback
and assign it to the session (more on callbacks below).
You should create and initialize a media session in the onCreate()
method of the
activity
or service that owns the session.
In order for media buttons to work
when your app is newly initialized (or stopped), its PlaybackState
must
contain a play action matching the intent that the media button sends. This is
why ACTION_PLAY
is assigned to the session state during
initialization. For more information, see Responding to Media
Buttons.
Maintain the playback state and metadata
There are two classes that represent the state of a media session.
The
PlaybackStateCompat
class describes the current operational state of the player. This includes:
- The transport state (whether the player is playing/paused/buffering, etc. See
getState()
) - An error code and optional error message, when applicable. (See
getErrorCode()
and read States and errors, below.) - The player position
- The valid controller actions that can be handled in the present state
The MediaMetadataCompat
class describes the material that is playing:
- The name of the artist, album, and track
- The track duration
- Album artwork for display on the lock screen. The image is a bitmap with a maximum size of 320x320dp (if larger, it's scaled down).
- An instance of
ContentUris
that points to a larger version of the artwork
The player state and metadata can change over the life of a media session. Every time the state or metadata changes, you must use the corresponding builder for each class, PlaybackStateCompat.Builder()
or MediaMetadataCompat.Builder()
, and then pass the new instance to the media session by calling
setPlaybackState()
or
setMetaData()
.
To reduce overall memory consumption from these frequent operations, it's a good idea to create the builders once and to reuse them throughout the life of the session.
States and errors
Note that PlaybackState
is an object that contains separate values for the
playback state of the session (getState()
)
and, when necessary, an associated error code (getErrorCode()
).
Errors can be fatal or non-fatal:
Whenever playback is interrupted, you should generate a fatal error: Set the
transport state to STATE_ERROR
and specify an associated error with setErrorMessage(int, CharSequence)
.
As long as playback is blocked by the error, the PlaybackState
should continue
to report STATE_ERROR
and the error.
A non-fatal error occurs when your app cannot handle a request, but can continue to play:
The transport remains in a "normal" state (such as STATE_PLAYING
) but the PlaybackState
holds an error code.
For example, if the last song is playing and the user requests a skip to next song,
playback can continue, but you should create a new PlaybackState
with the error code ERROR_CODE_END_OF_QUEUE
and
then call setPlaybackState()
. Media Controllers attached to the session will receive the callback
onPlaybackStateChanged()
and explain to the user what happened. A non-fatal error should only be reported once, at the time it occurs. The next time the session updates the PlaybackState
do not set the same non-fatal error again (unless the error occurred in response to a new request).
Media session lock screens
Starting with Android 4.0 (API level 14) the system can access a media session's playback state and metadata. This is how the lock screen can display media controls and artwork. The behavior varies depending on the Android version.
Album artwork
In Android 4.0 (API level 14) through Android 10 (API level 29), the background of the lock screen displays your album artwork - but only if the media session metadata includes a background bitmap.
Transport controls
In Android 4.0 (API level 14) through Android 4.4 (API level 19), when a media session is active and the media session metadata includes a background bitmap the lock screen automatically displays transport controls.
In Android 5.0 (API level 21) or greater the system does not provide transport controls on the lock screen. Instead, you should use a MediaStyle notification to display transport controls.
Add custom actions
Media applications can define custom actions; for example: thumbs up, like, or rewind 30 seconds. A custom action should implement completely new behavior. Do not use a custom action to replace one of the standard transport control actions defined in PlaybackStateCompat.
Add custom actions with addCustomAction()
. The following example shows how to add a control for a thumbs-up action:
Kotlin
stateBuilder.addCustomAction( PlaybackStateCompat.CustomAction.Builder( CUSTOM_ACTION_THUMBS_UP, resources.getString(R.string.thumbs_up), thumbsUpIcon ).run { setExtras(customActionExtras) build() } )
Java
stateBuilder.addCustomAction(new PlaybackStateCompat.CustomAction.Builder( CUSTOM_ACTION_THUMBS_UP, resources.getString(R.string.thumbs_up), thumbsUpIcon) .setExtras(customActionExtras) .build());
See the Universal Music Player for a complete example.
You respond to the action with onCustomAction()
.
Kotlin
override fun onCustomAction(action: String, extras: Bundle?) { when(action) { CUSTOM_ACTION_THUMBS_UP -> { ... } } }
Java
@Override public void onCustomAction(@NonNull String action, Bundle extras) { if (CUSTOM_ACTION_THUMBS_UP.equals(action)) { ... } }
Also see the Universal Music Player.
Media session callbacks
The main media session callback methods are onPlay()
, onPause()
, and onStop()
.
This is where you add the code that controls your player.
Since you instantiate and set the session's callback at runtime (in onCreate()
), your app can define alternative callbacks that use different players and choose the appropriate callback/player combination depending on the device and/or system level. You can change the player without changing the rest of the app. For example, you could use ExoPlayer when running on Android 4.1 (API level 16) or greater and use MediaPlayer
on earlier systems.
Besides controlling the player and managing the media session state transitions, callbacks also enable and disable features of your app and control the way it interacts with other apps and the device hardware. (See Controlling Audio Output).
The implementation of the media session callback methods depends on the structure of your app. See the separate pages that describe how to use callbacks in audio apps and video apps, describe how the callbacks should be implemented for each kind of app.