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The Google Assistant and Media Apps

The Google Assistant lets you use voice commands to control many devices, like Google Home, your phone, and more. It has a built-in capability to understand media commands ("play something by Beyonce") and supports media controls (like pause, skip, fast forward, thumbs up).

The Assistant communicates with Android media apps using a media session. It can use intents or services to launch your app and start playback. For the best results, your app should implement all the features described on this page.

This guide explains how to create a media app so that the Assistant can help a user control their media. To learn how Android apps use the Assist API to improve the assistant user experience, see Optimizing Content for the Assistant.

Use a media session

Every audio and video app must implement a media session so that the Assistant can operate the transport controls once playback has started.

Your app's media session must declare the actions it supports, and implement the corresponding media session callbacks. Declare your supported actions in setActions().

The Universal Music Player sample project is a good example of how to set up a media session.

Playback actions

In order to start playback from a service, a media session must have these these PLAY actions and their callbacks:

Action Callback
ACTION_PLAY onPlay()
ACTION_PLAY_FROM_SEARCH onPlayFromSearch()

Your session should also implement these PREPARE actions and their callbacks:

Action Callback
ACTION_PREPARE onPrepare()
ACTION_PREPARE_FROM_SEARCH onPrepareFromSearch()

By implementing the preparation APIs, the playback latency after a voice command can be reduced. Media apps that want to improve playback latency can use the extra time to start caching content and preparing media playback.

If onPrepare(), onPlay(), onPrepareFromSearch(), or onPlayFromSearch() are called without a search query, your media app should play the "current" media. If there is no current media, the app should try to play something.

Note that while the Assistant only uses the actions listed in this section, the best practice is to implement all preparation and playback APIs to ensure compatibility with other applications.

Transport controls

After your app's media session is active, the Assistant can issue voice commands to control playback and update media metadata. In order for this to work, your code should enable the following actions and implement the corresponding callbacks:

Action Callback Description
ACTION_SKIP_TO_NEXT onSkipToNext() Next video
ACTION_SKIP_TO_PREVIOUS onSkipToPrevious() Previous song
ACTION_PAUSE, ACTION_PLAY_PAUSE onPause() Pause
ACTION_STOP onStop() Stop
ACTION_PLAY onPlay() Resume
ACTION_SEEK_TO onSeekTo() Rewind by 30 seconds
ACTION_SET_RATING onSetRating(android.support.v4.media.RatingCompat) Thumbs up/down.

Please note:

Playback with an intent

The Assistant can launch an audio or video app and start playback by sending an intent with a deep link.

The intent and its deep link can come from different sources:

The Assistant adds the extra EXTRA_START_PLAYBACK with value true to the intent it sends to your app. Your app should start playback when it receives an intent with EXTRA_START_PLAYBACK.

Handling intents while active

Users can ask the Assistant to play something while your app is still playing content from a previous request. This means your app can receive new intents to start playback while its playback activity is already launched and active.

The activities that support intents with deep links should override onNewIntent() to handle new requests.

When starting playback, the Assistant might add additional flags to the intent it sends to your app. In particular, it may add FLAG_ACTIVITY_CLEAR_TOP or FLAG_ACTIVITY_NEW_TASK or both. Although your code does not need to handle these flags, the Android system responds to them. This might affect the behavior of your app when a second playback request with a new URI arrives while the previous URI is still playing. It's a good idea to test how your app responds in this case. You can use the adb command line tool to simulate the situation (the constant 335544320 is the boolean bitwise OR of the two flags):

adb shell 'am start -a android.intent.action.VIEW --ez android.intent.extra.START_PLAYBACK true -d <first_uri>' -f 335544320
adb shell 'am start -a android.intent.action.VIEW --ez android.intent.extra.START_PLAYBACK true -d <second_uri>' -f 335544320

Playback from a service

If your app has a media browser service that permits connections from the Assistant, the Assistant can start the app by communicating with the service's media session. The media browser service should never launch an Activity.

Be sure to set the MediaSession.Token when you initialize the media browser service. Remember to set the supported playback actions at all times, including during initialization. The Assistant expects your media app to set the playback actions before the Assistant sends the first playback command.

To start from a service, the Assistant implements the media browser client APIs. It performs TransportControls calls that trigger PLAY action callbacks on your app's media session.

The following diagram shows the order of calls generated by the Assistant and the corresponding media session callbacks. (The prepare callbacks are sent only if your app supports them.) All calls are asynchronous. The Assistant does not wait for any response from your app.

Starting playback with a media session

When a user issues a voice command to play, the Assistant responds with a short announcement. As soon as the announcement is complete the Assistant issues a PLAY action. It does not wait for any specific playback state.

If your app supports the ACTION_PREPARE_* actions, the Assistant calls the PREPARE action before starting the announcement.

Connecting to a MediaBrowserService

In order to use a service to start your app, the Assistant must be able to connect to the app's MediaBrowserService and retrieve its MediaSession.Token. Connection requests are handled in the service's onGetRoot() method. There are two ways to handle requests:

Accept all connection requests

You must return a BrowserRoot in order to allow the Assistant to send commands to your MediaSession. The easiest way is to allow all MediaBrowser apps to connect to your MediaBrowserService. You must return a non-null BrowserRoot. Here is the applicable code from the Universal Music Player:

@Override
public BrowserRoot onGetRoot(@NonNull String clientPackageName, int clientUid,
                             Bundle rootHints) {

    // To ensure you are not allowing any arbitrary app to browse your app's contents, you
    // need to check the origin:
    if (!mPackageValidator.isCallerAllowed(this, clientPackageName, clientUid)) {
        // If the request comes from an untrusted package, return an empty browser root.
        // If you return null, then the media browser will not be able to connect and
        // no further calls will be made to other media browsing methods.
        LogHelper.i(TAG, "OnGetRoot: Browsing NOT ALLOWED for unknown caller. "
                + "Returning empty browser root so all apps can use MediaController."
                + clientPackageName);
        return new MediaBrowserServiceCompat.BrowserRoot(MEDIA_ID_EMPTY_ROOT, null);
    }

    // Return browser roots for browsing...
}

Accept the Assistant app package and signature

You can explicitly allow the Assistant to connect to your media browser service by checking for its package name and signature. Your app will receive the package name in the onGetRoot method of your MediaBrowserService. You must return a BrowserRoot in order to allow the Assistant to send commands to your MediaSession. The Universal Music Player sample maintains a list of known package names and signatures. Below are the package names and signatures that are used by the Google Assistant.

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    Ev9lKTk+jkbqxbsh8nfBUapfKqYn0eidpwq2AzVp3juYl7//fKnaPhJD9gs=
</signing_certificate>

<signing_certificate name="Google" release="true"
                     package="com.google.android.googlequicksearchbox">
    MIIEQzCCAyugAwIBAgIJAMLgh0ZkSjCNMA0GCSqGSIb3DQEBBAUAMHQxCzAJBgNV
    BAYTAlVTMRMwEQYDVQQIEwpDYWxpZm9ybmlhMRYwFAYDVQQHEw1Nb3VudGFpbiBW
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</signing_certificate>
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