MediaRouter overview

In order to use the MediaRouter framework within your app, you must get an instance of the MediaRouter object and attach a MediaRouter.Callback object to listen for routing events. Content sent over a media route passes through the route's associated MediaRouteProvider (except in a few special cases, such as a Bluetooth output device). Figure 1 provides a high-level view of the classes used to route content between devices.

Figure 1. Overview of key media router classes used by apps.

Note: If you want your app to support Google Cast devices, you should use the Cast SDK and build your app as a Cast sender. Follow the directions in the Cast documentation instead of using the MediaRouter framework directly.

The media route button

Android apps should use a media route button to control media routing. The MediaRouter framework provides a standard interface for the button, which helps users recognize and use routing when it's available. The media route button is usually placed on the right side of your app's action bar, as shown in Figure 2.

Figure 2. Media route button in the action bar.

When the user presses the media route button, the available media routes appear in a list as shown in figure 3.

Figure 3. A list of available media routes, shown after pressing the media route button.

Follow these steps to create a media route button:

1. Use an AppCompatActivity
2. Define the media route button menu item
3. Create a MediaRouteSelector
4. Add the media route button to the action bar
5. Create and manage the MediaRouter.Callback methods in your activity's lifecycle

This section describes the first four steps. The next section describes Callback methods.

Use an AppCompatActivity

When you use the media router framework in an activity you should extend the activity from AppCompatActivity and import the package androidx.appcompat.app . You must add the androidx.appcompat:appcompat and androidx.mediarouter:mediarouter support libraries to your app development project. For more information on adding support libraries to your project, see Getting started with Android Jetpack.

Caution: Be sure to use the androidx implementation of the media router framework. Do not use the older android.media package.

Define the media route button menu item

Create an xml file that defines a menu item for the media route button. The item's action should be the MediaRouteActionProvider class. Here is an example file:

//myMediaRouteButtonMenuItem.xml
<?xmlversion="1.0"encoding="utf-8"?>
<menuxmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
>
<itemandroid:id="@+id/media_route_menu_item"
android:title="@string/media_route_menu_title"
app:actionProviderClass="androidx.mediarouter.app.MediaRouteActionProvider"
app:showAsAction="always"
/>
</menu>

Create a MediaRouteSelector

The routes that appear in the media route button menu are determined by a MediaRouteSelector . Extend your activity from AppCompatActivity and build the selector when the activity is created calling MediaRouteSelector.Builder from the onCreate() method as shown in the following code sample. Note that the selector is saved in a class variable, and the allowable route types are specified by adding MediaControlIntent objects:

classMediaRouterPlaybackActivity:AppCompatActivity(){
privatevarmSelector:MediaRouteSelector? =null
overridefunonCreate(savedInstanceState:Bundle?){
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// Create a route selector for the type of routes your app supports.
mSelector=MediaRouteSelector.Builder()
// These are the framework-supported intents
.addControlCategory(MediaControlIntent.CATEGORY_REMOTE_PLAYBACK)
.build()
}
}

publicclass MediaRouterPlaybackActivityextendsAppCompatActivity{
privateMediaRouteSelectormSelector;
@Override
protectedvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Create a route selector for the type of routes your app supports.
mSelector=newMediaRouteSelector.Builder()
// These are the framework-supported intents
.addControlCategory(MediaControlIntent.CATEGORY_REMOTE_PLAYBACK)
.build();
}
}

For most applications, the only route type needed is CATEGORY_REMOTE_PLAYBACK . This route type treats the device running your app as a remote control. The connected receiver device handles all content data retrieval, decoding, and playback. This is how apps that support Google Cast, like Chromecast, work.

A few manufacturers support a special routing option called "secondary output." With this routing, your media app retrieves, renders, and streams video or music directly to the screen and/or speakers on the selected remote receiver device. Use secondary output to send content to wireless-enabled music systems or video displays. To enable the discovery and selection of these devices, you need to add the CATEGORY_LIVE_AUDIO or CATEGORY_LIVE_VIDEO control categories to the MediaRouteSelector. You also need to create and handle your own Presentation dialog.

Add the media route button to the action bar

With the media route menu and MediaRouteSelector defined, you can now add the media route button to an activity. Override the onCreateOptionsMenu() method for each of your activities to add an options menu.

overridefunonCreateOptionsMenu(menu:Menu):Boolean{
super.onCreateOptionsMenu(menu)
// Inflate the menu and configure the media router action provider.
menuInflater.inflate(R.menu.sample_media_router_menu,menu)
// Attach the MediaRouteSelector to the menu item
valmediaRouteMenuItem=menu.findItem(R.id.media_route_menu_item)
valmediaRouteActionProvider=
MenuItemCompat.getActionProvider(mediaRouteMenuItem)asMediaRouteActionProvider
// Attach the MediaRouteSelector that you built in onCreate()
selector?.also(mediaRouteActionProvider::setRouteSelector)
// Return true to show the menu.
returntrue
}

@Override
publicbooleanonCreateOptionsMenu(Menumenu){
super.onCreateOptionsMenu(menu);
// Inflate the menu and configure the media router action provider.
getMenuInflater().inflate(R.menu.sample_media_router_menu,menu);
// Attach the MediaRouteSelector to the menu item
MenuItemmediaRouteMenuItem=menu.findItem(R.id.media_route_menu_item);
MediaRouteActionProvidermediaRouteActionProvider=
(MediaRouteActionProvider)MenuItemCompat.getActionProvider(
mediaRouteMenuItem);
// Attach the MediaRouteSelector that you built in onCreate()
mediaRouteActionProvider.setRouteSelector(selector);
// Return true to show the menu.
returntrue;
}

For more information about implementing the action bar in your app, see the Action Bar developer guide.

You can also add a media route button as a MediaRouteButton in any view. You must attach a MediaRouteSelector to the button using the setRouteSelector() method. See the Google Cast Design Checklist for guidelines on incorporating the media route button into your application.

MediaRouter callbacks

All the apps running on the same device share a single MediaRouter instance and its routes (filtered per app by the app's MediaRouteSelector). Each activity communicates with the MediaRouter using its own implementation of MediaRouter.Callback methods. The MediaRouter calls the callback methods whenever the user selects, changes, or disconnects a route.

There are several methods in the callback that you can override to receive information about routing events. At a minimum, your implementation of the MediaRouter.Callback class should override onRouteSelected() and onRouteUnselected() .

Since the MediaRouter is a shared resource, your app needs to manage its MediaRouter callbacks in response to the usual activity lifecycle callbacks:

• When the activity is created (onCreate(Bundle) ) grab a pointer to the MediaRouter and hold onto it for the lifetime of the app.
• Attach callbacks to MediaRouter when the activity becomes visible (onStart() ), and detach them when it is hidden (onStop() ).

The following code sample demonstrates how to create and save the callback object, how to obtain an instance of MediaRouter , and how to manage callbacks. Note the use of the CALLBACK_FLAG_REQUEST_DISCOVERY flag when attaching the callbacks in onStart() . This allows your MediaRouteSelector to refresh the media route button's list of available routes.

classMediaRouterPlaybackActivity:AppCompatActivity(){
privatevarmediaRouter:MediaRouter? =null
privatevarmSelector:MediaRouteSelector? =null
// Variables to hold the currently selected route and its playback client
privatevarmRoute:MediaRouter.RouteInfo?=null
privatevarremotePlaybackClient:RemotePlaybackClient? =null
// Define the Callback object and its methods, save the object in a class variable
privatevalmediaRouterCallback=object:MediaRouter.Callback(){
overridefunonRouteSelected(router:MediaRouter,route:MediaRouter.RouteInfo){
Log.d(TAG,"onRouteSelected: route=$route")
if(route.supportsControlCategory(MediaControlIntent.CATEGORY_REMOTE_PLAYBACK)){
// Stop local playback (if necessary)
// ...
// Save the new route
mRoute=route
// Attach a new playback client
remotePlaybackClient=
RemotePlaybackClient(this@MediaRouterPlaybackActivity,mRoute)
// Start remote playback (if necessary)
// ...
}
}
overridefunonRouteUnselected(
router:MediaRouter,
route:MediaRouter.RouteInfo,
reason:Int
){
Log.d(TAG,"onRouteUnselected: route=$route")
if(route.supportsControlCategory(MediaControlIntent.CATEGORY_REMOTE_PLAYBACK)){
// Changed route: tear down previous client
mRoute?.also{
remotePlaybackClient?.release()
remotePlaybackClient=null
}
// Save the new route
mRoute=route
when(reason){
MediaRouter.UNSELECT_REASON_ROUTE_CHANGED->{
// Resume local playback (if necessary)
// ...
}
}
}
}
}
// Retain a pointer to the MediaRouter
overridefunonCreate(savedInstanceState:Bundle?){
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// Get the media router service.
mediaRouter=MediaRouter.getInstance(this)
...
}
// Use this callback to run your MediaRouteSelector to generate the
// list of available media routes
overridefunonStart(){
mSelector?.also{selector->
mediaRouter?.addCallback(selector,mediaRouterCallback,
MediaRouter.CALLBACK_FLAG_REQUEST_DISCOVERY)
}
super.onStart()
}
// Remove the selector on stop to tell the media router that it no longer
// needs to discover routes for your app.
overridefunonStop(){
mediaRouter?.removeCallback(mediaRouterCallback)
super.onStop()
}
...
}

publicclass MediaRouterPlaybackActivityextendsAppCompatActivity{
privateMediaRoutermediaRouter;
privateMediaRouteSelectormSelector;
// Variables to hold the currently selected route and its playback client
privateMediaRouter.RouteInfomRoute;
privateRemotePlaybackClientremotePlaybackClient;
// Define the Callback object and its methods, save the object in a class variable
privatefinalMediaRouter.CallbackmediaRouterCallback=
newMediaRouter.Callback(){
@Override
publicvoidonRouteSelected(MediaRouterrouter,RouteInforoute){
Log.d(TAG,"onRouteSelected: route="+route);
if(route.supportsControlCategory(
MediaControlIntent.CATEGORY_REMOTE_PLAYBACK)){
// Stop local playback (if necessary)
// ...
// Save the new route
mRoute=route;
// Attach a new playback client
remotePlaybackClient=newRemotePlaybackClient(this,mRoute);
// Start remote playback (if necessary)
// ...
}
}
@Override
publicvoidonRouteUnselected(MediaRouterrouter,RouteInforoute,intreason){
Log.d(TAG,"onRouteUnselected: route="+route);
if(route.supportsControlCategory(
MediaControlIntent.CATEGORY_REMOTE_PLAYBACK)){
// Changed route: tear down previous client
if(mRoute!=null && remotePlaybackClient!=null){
remotePlaybackClient.release();
remotePlaybackClient=null;
}
// Save the new route
mRoute=route;
if(reason!=MediaRouter.UNSELECT_REASON_ROUTE_CHANGED){
// Resume local playback (if necessary)
// ...
}
}
}
}
// Retain a pointer to the MediaRouter
@Override
protectedvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Get the media router service.
mediaRouter=MediaRouter.getInstance(this);
...
}
// Use this callback to run your MediaRouteSelector to generate the list of available media routes
@Override
publicvoidonStart(){
mediaRouter.addCallback(mSelector,mediaRouterCallback,
MediaRouter.CALLBACK_FLAG_REQUEST_DISCOVERY);
super.onStart();
}
// Remove the selector on stop to tell the media router that it no longer
// needs to discover routes for your app.
@Override
publicvoidonStop(){
mediaRouter.removeCallback(mediaRouterCallback);
super.onStop();
}
...
}

The media router framework also provides a MediaRouteDiscoveryFragment class, which takes care of adding and removing the callback for an activity.

Note: If you are writing a music playback app and want the app to play music while it is in the background, you must build a Service for playback and call the media router framework from the Service's lifecycle callbacks.

Controlling a remote playback route

When you select a remote playback route your app acts as a remote control. The device at the other end of the route handles all content data retrieval, decoding, and playback functions. The controls in your app's UI communicate with the receiver device using a RemotePlaybackClient object.

The RemotePlaybackClient class provides additional methods for managing content playback. Here are a few of the key playback methods from the RemotePlaybackClient class:

• play() — Play a specific media file, specified by a Uri .
• pause() — Pause the currently playing media track.
• resume() — Continue playing the current track after a pause command.
• seek() — Move to a specific position in the current track.
• release() — Tear down the connection from your app to the remote playback device.

You can use these methods to attach actions to the playback controls that you provide in your app. Most of these methods also allow you to include a callback object so you can monitor the progress of the playback task or control request.

The RemotePlaybackClient class also supports queueing of multiple media items for playback and management of the media queue.

Sample code

The Android BasicMediaRouter and MediaRouter samples further demonstrate the use of the MediaRouter API.