Build media apps for cars

Android Auto and Android Automotive OS help you bring your media app content to users in their car. A media app for cars must provide a media browser service so that Android Auto and Android Automotive OS, or another app with a media browser, can discover and display your content.

This guide assumes that you already have a media app that plays audio on a phone and that your media app conforms to the Android media app architecture.

This guide describes the required components of a MediaBrowserService and MediaSession that your app needs in order to work on Android Auto or Android Automotive OS. After you have completed the core media infrastructure, you can add support for Android Auto and add support for Android Automotive OS to your media app.

Before you begin

  1. Review the Android media API documentation.
  2. Review Create media apps for design guidance.
  3. Review the key terms and concepts listed in this section.

Key terms and concepts

Media browser service
An Android service implemented by your media app that complies with the MediaBrowserServiceCompat API. Your app uses this service to expose its content.
Media browser
An API used by media apps to discover media browser services and display their content. Android Auto and Android Automotive OS use a media browser to find your app's media browser service.
Media item

The media browser organizes its content in a tree of MediaItem objects. A media item can have either or both of the following flags:

  • FLAG_PLAYABLE: indicates that the item is a leaf on the content tree. The item represents a single sound stream, such as a song on an album, a chapter in an audio book, or an episode of a podcast.
  • FLAG_BROWSABLE: indicates that the item is a node on the content tree and it has children. For example, the item represents an album, and its children are the songs on the album.

A media item that is both browsable and playable acts like a playlist. You can select the item itself to play all of its children, or you can browse its children.

Vehicle-optimized

An activity for an Android Automotive OS app that adheres to the Android Automotive OS design guidelines. The interface for these activities is not drawn by Android Automotive OS, so you must ensure that your app adheres to the design guidelines. Typically, this includes larger tap targets and font sizes, support for day and night modes, and higher contrast ratios.

Vehicle-optimized user interfaces are only allowed to be displayed when Car User Experience Restrictions (CUXRs) are not in effect, because these interfaces can require extended attention or interaction from the user. CUXRs are not in effect when the car is stopped or parked but are always in effect when the car is in motion.

You don't need to design activities for Android Auto, because Android Auto draws its own vehicle-optimized interface using the information from your media browser service.

Configure your app's manifest files

Before you can create your media browser service, you need to configure your app's manifest files.

Declare your media browser service

Both Android Auto and Android Automotive OS connect to your app through your media browser service to browse media items. Declare your media browser service in your manifest to let Android Auto and Android Automotive OS discover the service and connect to your app.

The following code snippet shows how to declare your media browser service in your manifest. Include this code in the manifest file for your Android Automotive OS module and in the manifest file for your phone app.

<application>
    ...
    <service android:name=".MyMediaBrowserService"
             android:exported="true">
        <intent-filter>
            <action android:name="android.media.browse.MediaBrowserService"/>
        </intent-filter>
    </service>
    ...
</application>

Specify app icons

You need to specify app icons that Android Auto and Android Automotive OS can use to represent your app in the system UI. Two icon types are required:

  • Launcher icon
  • Attribution icon

Launcher icon

The launcher icon represents your app in the system UI, such as on the launcher and in the tray of icons. You can specify that you want to use the icon from your mobile app to represent your car media app using the following manifest declaration:

<application
    ...
    android:icon="@mipmap/ic_launcher"
    ...
/>

To use a different icon than your mobile app's, set the android:icon property on your media browser service's <service> element in the manifest:

<application>
    ...
    <service
        ...
        android:icon="@mipmap/auto_launcher"
        ...
    />
</application>

Attribution icon

Figure 1. Attribution icon on media card.

The attribution icon is used in places where media content takes precedence, such as on media cards. Consider reusing the small icon used for notifications. This icon must be monochrome. You can specify an icon that is used to represent your app using the following manifest declaration:

<application>
    ...
    <meta-data
        android:name="androidx.car.app.TintableAttributionIcon"
        android:resource="@drawable/ic_status_icon" />
    ...
</application>

Create your media browser service

You create a media browser service by extending the MediaBrowserServiceCompat class. Both Android Auto and Android Automotive OS can then use your service to do the following:

  • Browse your app's content hierarchy to present a menu to the user.
  • Get the token for your app's MediaSessionCompat object to control audio playback.

You can also use your media browser service to let other clients access media content from your app. These media clients might be other apps on a user's phone, or they can be other remote clients.

Media browser service workflow

This section describes how Android Automotive OS and Android Auto interact with your media browser service during a typical user workflow.

  1. The user launches your app on Android Automotive OS or Android Auto.
  2. Android Automotive OS or Android Auto contacts your app's media browser service using the onCreate() method. In your implementation of the onCreate() method, you must create and register a MediaSessionCompat object and its callback object.
  3. Android Automotive OS or Android Auto calls your service's onGetRoot() method to get the root media item in your content hierarchy. The root media item is not displayed; instead, it's used to retrieve more content from your app.
  4. Android Automotive OS or Android Auto calls your service's onLoadChildren() method to get the children of the root media item. Android Automotive OS and Android Auto display these media items as the top level of content items. See Structure the root menu on this page for more information on what the system expects at this level.
  5. If the user selects a browsable media item, your service's onLoadChildren() method is called again to retrieve the children of the selected menu item.
  6. If the user selects a playable media item, Android Automotive OS or Android Auto calls the appropriate media session callback method to perform that action.
  7. If supported by your app, the user can also search your content. In this case, Android Automotive OS or Android Auto call your service's onSearch() method.

Build your content hierarchy

Android Auto and Android Automotive OS call your app's media browser service to find out what content is available. You need to implement two methods in your media browser service to support this: onGetRoot() and onLoadChildren()

Implement onGetRoot

Your service's onGetRoot() method returns information about the root node of your content hierarchy. Android Auto and Android Automotive OS use this root node to request the rest of your content using the onLoadChildren() method.

The following code snippet shows a simple implementation of the onGetRoot() method:

Kotlin

override fun onGetRoot(
    clientPackageName: String,
    clientUid: Int,
    rootHints: Bundle?
): BrowserRoot? =
    // Verify that the specified package is allowed to access your
    // content. You'll need to write your own logic to do this.
    if (!isValid(clientPackageName, clientUid)) {
        // If the request comes from an untrusted package, return null.
        // No further calls will be made to other media browsing methods.

        null
    } else MediaBrowserServiceCompat.BrowserRoot(MY_MEDIA_ROOT_ID, null)

Java

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

    // Verify that the specified package is allowed to access your
    // content. You'll need to write your own logic to do this.
    if (!isValid(clientPackageName, clientUid)) {
        // If the request comes from an untrusted package, return null.
        // No further calls will be made to other media browsing methods.

        return null;
    }

    return new MediaBrowserServiceCompat.BrowserRoot(MY_MEDIA_ROOT_ID, null);
}

For a more detailed example of this method, see the onGetRoot() method in the Universal Android Music Player sample app on GitHub.

Add package validation for onGetRoot()

When a call is made to your service's onGetRoot() method, the calling package passes identifying information to your service. Your service can use this information to decide whether that package can access your content. For example, you can restrict access to your app's content to a list of approved packages by comparing the clientPackageName to your allowlist and verifying the certificate used to sign the package's APK. If the package can't be verified, return null to deny access to your content.

To provide system apps, such as Android Auto and Android Automotive OS, with access to your content, your service must always return a non-null BrowserRoot when these system apps call the onGetRoot() method. The signature of the Android Automotive OS system app can vary depending on the make and model of the car, so you need to permit connections from all system apps to support Android Automotive OS robustly.

The following code snippet shows how your service can validate that the calling package is a system app:

fun isKnownCaller(
    callingPackage: String,
    callingUid: Int
): Boolean {
    ...
    val isCallerKnown = when {
       // If the system is making the call, allow it.
       callingUid == Process.SYSTEM_UID -> true
       // If the app was signed by the same certificate as the platform
       // itself, also allow it.
       callerSignature == platformSignature -> true
       // ... more cases
    }
    return isCallerKnown
}

This code snippet is an excerpt from the PackageValidator class in the Universal Android Music Player sample app on GitHub. See that class for a more detailed example of how to implement package validation for your service's onGetRoot() method.

In addition to allowing system apps, you must let the Google Assistant connect to your MediaBrowserService. Note that the Google Assistant has separate package names for the phone, which includes Android Auto, and for Android Automotive OS.

Implement onLoadChildren()

After receiving your root node object, Android Auto and Android Automotive OS build a top-level menu by calling onLoadChildren() on the root node object to get its children. Client apps build submenus by calling this same method using child node objects.

Each node in your content hierarchy is represented by a MediaBrowserCompat.MediaItem object. Each of these media items is identified by a unique ID string. Client apps treat these ID strings as opaque tokens. When a client app wants to browse to a submenu, or play a media item, it passes the token. Your app is responsible for associating the token with the appropriate media item.

The following code snippet shows a simple implementation of onLoadChildren() method:

Kotlin

override fun onLoadChildren(
    parentMediaId: String,
    result: Result<List<MediaBrowserCompat.MediaItem>>
) {
    // Assume for example that the music catalog is already loaded/cached.

    val mediaItems: MutableList<MediaBrowserCompat.MediaItem> = mutableListOf()

    // Check whether this is the root menu:
    if (MY_MEDIA_ROOT_ID == parentMediaId) {

        // Build the MediaItem objects for the top level
        // and put them in the mediaItems list.
    } else {

        // Examine the passed parentMediaId to see which submenu we're at
        // and put the children of that menu in the mediaItems list.
    }
    result.sendResult(mediaItems)
}

Java

@Override
public void onLoadChildren(final String parentMediaId,
    final Result<List<MediaBrowserCompat.MediaItem>> result) {

    // Assume for example that the music catalog is already loaded/cached.

    List<MediaBrowserCompat.MediaItem> mediaItems = new ArrayList<>();

    // Check whether this is the root menu:
    if (MY_MEDIA_ROOT_ID.equals(parentMediaId)) {

        // Build the MediaItem objects for the top level
        // and put them in the mediaItems list.
    } else {

        // Examine the passed parentMediaId to see which submenu we're at
        // and put the children of that menu in the mediaItems list.
    }
    result.sendResult(mediaItems);
}

For a complete example of this method, see the onLoadChildren() method in the Universal Android Music Player sample app on GitHub.

Structure the root menu

Figure 2. Root content displayed as navigational tabs.

Android Auto and Android Automotive OS have specific constraints about the structure of the root menu. These are communicated to the MediaBrowserService through root hints, which can be read through the Bundle argument passed into onGetRoot(). Following these hints lets the system display the root content optimally as navigational tabs. If you don't follow these hints, some root content might be dropped or made less discoverable by the system. Two hints are sent:

Use the following code to read the relevant root hints:

Kotlin

import androidx.media.utils.MediaConstants

// Later, in your MediaBrowserServiceCompat.
override fun onGetRoot(
    clientPackageName: String,
    clientUid: Int,
    rootHints: Bundle
): BrowserRoot {

  val maximumRootChildLimit = rootHints.getInt(
      MediaConstants.BROWSER_ROOT_HINTS_KEY_ROOT_CHILDREN_LIMIT,
      /* defaultValue= */ 4)
  val supportedRootChildFlags = rootHints.getInt(
      MediaConstants.BROWSER_ROOT_HINTS_KEY_ROOT_CHILDREN_SUPPORTED_FLAGS,
      /* defaultValue= */ MediaItem.FLAG_BROWSABLE)

  // Rest of method...
}

Java

import androidx.media.utils.MediaConstants;

// Later, in your MediaBrowserServiceCompat.
@Override
public BrowserRoot onGetRoot(
    String clientPackageName, int clientUid, Bundle rootHints) {

    int maximumRootChildLimit = rootHints.getInt(
        MediaConstants.BROWSER_ROOT_HINTS_KEY_ROOT_CHILDREN_LIMIT,
        /* defaultValue= */ 4);
    int supportedRootChildFlags = rootHints.getInt(
        MediaConstants.BROWSER_ROOT_HINTS_KEY_ROOT_CHILDREN_SUPPORTED_FLAGS,
        /* defaultValue= */ MediaItem.FLAG_BROWSABLE);

    // Rest of method...
}

You can choose to branch the logic for the structure of your content hierarchy based on the values of these hints, particularly if your hierarchy varies among MediaBrowser integrations outside of Android Auto and Android Automotive OS. For example, if you normally show a root playable item, you might want to nest it under a root browsable item instead due to the value of the supported flags hint.

Apart from the root hints, there are a couple additional guidelines to follow to help ensure that tabs render optimally:

  • Supply monochrome, preferably white, icons for each tab item.
  • Supply short but meaningful labels for each tab item. Keeping labels short reduces the chance of the strings being truncated.

Display media artwork

Artwork for media items must be passed as a local URI using either ContentResolver.SCHEME_CONTENT or ContentResolver.SCHEME_ANDROID_RESOURCE. This local URI must resolve to either a bitmap or a vector drawable in the application’s resources. For MediaDescriptionCompat objects representing items in the content hierarchy, pass the URI through setIconUri(). For MediaMetadataCompat objects representing the currently playing item, pass the URI through putString(), using any of the following keys:

The following steps describe how to download art from a web URI and expose it through a local URI. For a more complete example, see the implementation of openFile() and the surrounding methods in the Universal Android Music Player sample app.

  1. Build a content:// URI corresponding to the web URI. The media browser service and media session pass this content URI to Android Auto and Android Automotive OS.

    Kotlin

    fun Uri.asAlbumArtContentURI(): Uri {
  return Uri.Builder()
    .scheme(ContentResolver.SCHEME_CONTENT)
    .authority(CONTENT_PROVIDER_AUTHORITY)
    .appendPath(this.getPath()) // Make sure you trust the URI
    .build()
}

    Java

    public static Uri asAlbumArtContentURI(Uri webUri) {
  return new Uri.Builder()
    .scheme(ContentResolver.SCHEME_CONTENT)
    .authority(CONTENT_PROVIDER_AUTHORITY)
    .appendPath(webUri.getPath()) // Make sure you trust the URI!
    .build();
}

  2. In your implementation of ContentProvider.openFile(), check whether a file exists for the corresponding URI. If not, download and cache the image file. The following code snippet uses Glide.

    Kotlin

    override fun openFile(uri: Uri, mode: String): ParcelFileDescriptor? {
  val context = this.context ?: return null
  val file = File(context.cacheDir, uri.path)
  if (!file.exists()) {
    val remoteUri = Uri.Builder()
        .scheme("https")
        .authority("my-image-site")
        .appendPath(uri.path)
        .build()
    val cacheFile = Glide.with(context)
        .asFile()
        .load(remoteUri)
        .submit()
        .get(DOWNLOAD_TIMEOUT_SECONDS, TimeUnit.SECONDS)

    cacheFile.renameTo(file)
    file = cacheFile
  }
  return ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY)
}

    Java

    @Nullable
@Override
public ParcelFileDescriptor openFile(@NonNull Uri uri, @NonNull String mode)
    throws FileNotFoundException {
  Context context = this.getContext();
  File file = new File(context.getCacheDir(), uri.getPath());
  if (!file.exists()) {
    Uri remoteUri = new Uri.Builder()
        .scheme("https")
        .authority("my-image-site")
        .appendPath(uri.getPath())
        .build();
    File cacheFile = Glide.with(context)
        .asFile()
        .load(remoteUri)
        .submit()
        .get(DOWNLOAD_TIMEOUT_SECONDS, TimeUnit.SECONDS);

    cacheFile.renameTo(file);
    file = cacheFile;
  }
  return ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY);
}

For more details about content providers, refer to Creating a content provider.

Apply content styles

After building your content hierarchy using browsable or playable items, you can apply content styles that determine how those items display in the car.

You can use the following content styles:

List items

This content style prioritizes titles and metadata over images.

Grid items

This content style prioritizes images over titles and metadata.

Set default content styles

You can set global defaults for how your media items are displayed by including certain constants in the BrowserRoot extras bundle of your service's onGetRoot() method. Android Auto and Android Automotive OS read this bundle and look for those constants to determine the appropriate style.

The following extras can be used as keys in the bundle:

The keys can map to the following integer constant values to influence the presentation of those items:

The following code snippet shows how to set the default content style for browsable items to grids and playable items to lists:

Kotlin

import androidx.media.utils.MediaConstants

@Nullable
override fun onGetRoot(
    @NonNull clientPackageName: String,
    clientUid: Int,
    @Nullable rootHints: Bundle
): BrowserRoot {
    val extras = Bundle()
    extras.putInt(
        MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_BROWSABLE,
        MediaConstants.DESCRIPTION_EXTRAS_VALUE_CONTENT_STYLE_GRID_ITEM)
    extras.putInt(
        MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_PLAYABLE,
        MediaConstants.DESCRIPTION_EXTRAS_VALUE_CONTENT_STYLE_LIST_ITEM)
    return BrowserRoot(ROOT_ID, extras)
}

Java

import androidx.media.utils.MediaConstants;

@Nullable
@Override
public BrowserRoot onGetRoot(
    @NonNull String clientPackageName,
    int clientUid,
    @Nullable Bundle rootHints) {
    Bundle extras = new Bundle();
    extras.putInt(
        MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_BROWSABLE,
        MediaConstants.DESCRIPTION_EXTRAS_VALUE_CONTENT_STYLE_GRID_ITEM);
    extras.putInt(
        MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_PLAYABLE,
        MediaConstants.DESCRIPTION_EXTRAS_VALUE_CONTENT_STYLE_LIST_ITEM);
    return new BrowserRoot(ROOT_ID, extras);
}

Set per-item content styles

The Content Style API lets you override the default content style for any browsable media item's children, as well as any media item itself.

To override the default for a browsable media item's children, create an extras bundle in the MediaDescription of the media item and add the same previously mentioned hints. DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_PLAYABLE applies to that item's playable children, while DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_BROWSABLE applies to that item's browsable children.

To override the default for a particular media item itself, not its children, create an extras bundle in the MediaDescription of the media item and add a hint with the key DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_SINGLE_ITEM. Use the same values described previously to specify that item's presentation.

The following code snippet shows how to create a browsable MediaItem that overrides the default content style for both itself and its children. It styles itself as a category list item, its browsable children as list items, and its playable children as grid items:

Kotlin

import androidx.media.utils.MediaConstants

private fun createBrowsableMediaItem(
    mediaId: String,
    folderName: String,
    iconUri: Uri
): MediaBrowser.MediaItem {
    val mediaDescriptionBuilder = MediaDescription.Builder()
    mediaDescriptionBuilder.setMediaId(mediaId)
    mediaDescriptionBuilder.setTitle(folderName)
    mediaDescriptionBuilder.setIconUri(iconUri)
    val extras = Bundle()
    extras.putInt(
        MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_SINGLE_ITEM,
        MediaConstants.DESCRIPTION_EXTRAS_VALUE_CONTENT_STYLE_CATEGORY_LIST_ITEM)
    extras.putInt(
        MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_BROWSABLE,
        MediaConstants.DESCRIPTION_EXTRAS_VALUE_CONTENT_STYLE_LIST_ITEM)
    extras.putInt(
        MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_PLAYABLE,
        MediaConstants.DESCRIPTION_EXTRAS_VALUE_CONTENT_STYLE_GRID_ITEM)
    mediaDescriptionBuilder.setExtras(extras)
    return MediaBrowser.MediaItem(
        mediaDescriptionBuilder.build(), MediaBrowser.MediaItem.FLAG_BROWSABLE)
}

Java

import androidx.media.utils.MediaConstants;

private MediaBrowser.MediaItem createBrowsableMediaItem(
    String mediaId,
    String folderName,
    Uri iconUri) {
    MediaDescription.Builder mediaDescriptionBuilder = new MediaDescription.Builder();
    mediaDescriptionBuilder.setMediaId(mediaId);
    mediaDescriptionBuilder.setTitle(folderName);
    mediaDescriptionBuilder.setIconUri(iconUri);
    Bundle extras = new Bundle();
    extras.putInt(
        MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_SINGLE_ITEM,
        MediaConstants.DESCRIPTION_EXTRAS_VALUE_CONTENT_STYLE_CATEGORY_LIST_ITEM);
    extras.putInt(
        MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_BROWSABLE,
        MediaConstants.DESCRIPTION_EXTRAS_VALUE_CONTENT_STYLE_LIST_ITEM);
    extras.putInt(
        MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_PLAYABLE,
        MediaConstants.DESCRIPTION_EXTRAS_VALUE_CONTENT_STYLE_GRID_ITEM);
    mediaDescriptionBuilder.setExtras(extras);
    return new MediaBrowser.MediaItem(
        mediaDescriptionBuilder.build(), MediaBrowser.MediaItem.FLAG_BROWSABLE);
}

Group items using title hints

To group related media items together, you use a per-item hint. Every media item in a group needs to declare an extras bundle in their MediaDescription that includes a mapping with the key DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_GROUP_TITLE and an identical string value. Localize this string, which is used as the title of the group.

The following code snippet shows how to create a MediaItem with a subgroup heading of "Songs":

Kotlin

import androidx.media.utils.MediaConstants

private fun createMediaItem(
    mediaId: String,
    folderName: String,
    iconUri: Uri
): MediaBrowser.MediaItem {
    val mediaDescriptionBuilder = MediaDescription.Builder()
    mediaDescriptionBuilder.setMediaId(mediaId)
    mediaDescriptionBuilder.setTitle(folderName)
    mediaDescriptionBuilder.setIconUri(iconUri)
    val extras = Bundle()
    extras.putString(
        MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_GROUP_TITLE,
        "Songs")
    mediaDescriptionBuilder.setExtras(extras)
    return MediaBrowser.MediaItem(
        mediaDescriptionBuilder.build(), /* playable or browsable flag*/)
}

Java

import androidx.media.utils.MediaConstants;

private MediaBrowser.MediaItem createMediaItem(String mediaId, String folderName, Uri iconUri) {
   MediaDescription.Builder mediaDescriptionBuilder = new MediaDescription.Builder();
   mediaDescriptionBuilder.setMediaId(mediaId);
   mediaDescriptionBuilder.setTitle(folderName);
   mediaDescriptionBuilder.setIconUri(iconUri);
   Bundle extras = new Bundle();
   extras.putString(
       MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_GROUP_TITLE,
       "Songs");
   mediaDescriptionBuilder.setExtras(extras);
   return new MediaBrowser.MediaItem(
       mediaDescriptionBuilder.build(), /* playable or browsable flag*/);
}

Your app must pass all the media items that you want to group together as a contiguous block. For example, suppose that you want to display two groups of media items, "Songs" and "Albums," in that order, and your app passes in five media items in the following order:

  1. Media item A with extras.putString(MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_GROUP_TITLE, "Songs")
  2. Media item B with extras.putString(MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_GROUP_TITLE, "Albums")
  3. Media item C with extras.putString(MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_GROUP_TITLE, "Songs")
  4. Media item D with extras.putString(MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_GROUP_TITLE, "Songs")
  5. Media item E with extras.putString(MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_GROUP_TITLE, "Albums")

Because the media items for the "Songs" group and "Albums" group are not kept together in contiguous blocks, Android Auto and Android Automotive OS interprets this as the following four groups:

  • Group 1 called "Songs" containing media item A
  • Group 2 called "Albums" containing media item B
  • Group 3 called "Songs" containing media items C and D
  • Group 4 called "Albums" containing media item E

To display these items in two groups, your app must pass the media items in the following order instead:

  1. Media item A with extras.putString(MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_GROUP_TITLE, "Songs")
  2. Media item C with extras.putString(MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_GROUP_TITLE, "Songs")
  3. Media item D with extras.putString(MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_GROUP_TITLE, "Songs")
  4. Media item B with extras.putString(MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_GROUP_TITLE, "Albums")
  5. Media item E with extras.putString(MediaConstants.DESCRIPTION_EXTRAS_KEY_CONTENT_STYLE_GROUP_TITLE, "Albums")

Display additional metadata indicators

You can include additional metadata indicators to provide at-a-glance information for content in the media browser tree and during playback. Within the browse tree, Android Auto and Android Automotive OS read the extras associated with an item and look for certain constants to determine which indicators to display. During media playback, Android Auto and Android Automotive OS read the metadata for the media session and look for certain constants to determine indicators to display.

Figure 3. Playback view with metadata identifying the song and artist as well as an icon indicating explicit content.

Figure 4. Browse view with a dot for unplayed content on the first item and a progress bar for partially played content on the second item.

The following constants can be used in both MediaItem description extras and MediaMetadata extras:

The following constants can only be used in MediaItem description extras:

To display indicators that appear while the user is browsing the media browse tree, create an extras bundle that includes one or more of these constants and pass that bundle to the MediaDescription.Builder.setExtras() method.

The following code snippet shows how to display indicators for an explicit media item that is 70% complete:

Kotlin

import androidx.media.utils.MediaConstants

val extras = Bundle()
extras.putLong(
    MediaConstants.METADATA_KEY_IS_EXPLICIT,
    MediaConstants.METADATA_VALUE_ATTRIBUTE_PRESENT)
extras.putInt(
    MediaConstants.DESCRIPTION_EXTRAS_KEY_COMPLETION_STATUS,
    MediaConstants.DESCRIPTION_EXTRAS_VALUE_COMPLETION_STATUS_PARTIALLY_PLAYED)
extras.putDouble(
    MediaConstants.DESCRIPTION_EXTRAS_KEY_COMPLETION_PERCENTAGE, 0.7)
val description =
    MediaDescriptionCompat.Builder()
        .setMediaId(/*...*/)
        .setTitle(resources.getString(/*...*/))
        .setExtras(extras)
        .build()
return MediaBrowserCompat.MediaItem(description, /* flags */)

Java

import androidx.media.utils.MediaConstants;

Bundle extras = new Bundle();
extras.putLong(
    MediaConstants.METADATA_KEY_IS_EXPLICIT,
    MediaConstants.METADATA_VALUE_ATTRIBUTE_PRESENT);
extras.putInt(
    MediaConstants.DESCRIPTION_EXTRAS_KEY_COMPLETION_STATUS,
    MediaConstants.DESCRIPTION_EXTRAS_VALUE_COMPLETION_STATUS_PARTIALLY_PLAYED);
extras.putDouble(
    MediaConstants.DESCRIPTION_EXTRAS_KEY_COMPLETION_PERCENTAGE, 0.7);
MediaDescriptionCompat description =
    new MediaDescriptionCompat.Builder()
        .setMediaId(/*...*/)
        .setTitle(resources.getString(/*...*/))
        .setExtras(extras)
        .build();
return new MediaBrowserCompat.MediaItem(description, /* flags */);

To display indicators for a media item that is currently being played, you can declare Long values for METADATA_KEY_IS_EXPLICIT or EXTRA_DOWNLOAD_STATUS in the MediaMetadataCompat of your mediaSession. You can't display the DESCRIPTION_EXTRAS_KEY_COMPLETION_STATUS or DESCRIPTION_EXTRAS_KEY_COMPLETION_PERCENTAGE indicators on the playback view.

The following code snippet shows how to indicate that the current song in the playback view is explicit and downloaded:

Kotlin

import androidx.media.utils.MediaConstants

mediaSession.setMetadata(
    MediaMetadataCompat.Builder()
        .putString(
            MediaMetadataCompat.METADATA_KEY_DISPLAY_TITLE, "Song Name")
        .putString(
            MediaMetadataCompat.METADATA_KEY_DISPLAY_SUBTITLE, "Artist name")
        .putString(
            MediaMetadataCompat.METADATA_KEY_ALBUM_ART_URI,
            albumArtUri.toString())
        .putLong(
            MediaConstants.METADATA_KEY_IS_EXPLICIT,
            MediaConstants.METADATA_VALUE_ATTRIBUTE_PRESENT)
        .putLong(
            MediaDescriptionCompat.EXTRA_DOWNLOAD_STATUS,
            MediaDescriptionCompat.STATUS_DOWNLOADED)
        .build())

Java

import androidx.media.utils.MediaConstants;

mediaSession.setMetadata(
    new MediaMetadataCompat.Builder()
        .putString(
            MediaMetadataCompat.METADATA_KEY_DISPLAY_TITLE, "Song Name")
        .putString(
            MediaMetadataCompat.METADATA_KEY_DISPLAY_SUBTITLE, "Artist name")
        .putString(
            MediaMetadataCompat.METADATA_KEY_ALBUM_ART_URI,
            albumArtUri.toString())
        .putLong(
            MediaConstants.METADATA_KEY_IS_EXPLICIT,
            MediaConstants.METADATA_VALUE_ATTRIBUTE_PRESENT)
        .putLong(
            MediaDescriptionCompat.EXTRA_DOWNLOAD_STATUS,
            MediaDescriptionCompat.STATUS_DOWNLOADED)
        .build());

Update the progress bar in the browse view as content is playing

As previously mentioned, you can use the DESCRIPTION_EXTRAS_KEY_COMPLETION_PERCENTAGE extra to show a progress bar for partially played content in the browse view. However, if a user continues playing the partially played content from Android Auto or Android Automotive OS, that indicator becomes inaccurate as time passes.

For Android Auto and Android Automotive OS to keep the progress bar up to date, you can supply additional information in MediaMetadataCompat and PlaybackStateCompat to link ongoing content to media items in the browse view. The following requirements must be met for the media item to have an automatically updating progress bar:

The following code snippet shows how to indicate that the currently playing item is linked to an item in the browse view:

Kotlin

import androidx.media.utils.MediaConstants

// When the MediaItem is constructed to show in the browse view.
// Suppose the item was 25% complete when the user launched the browse view.
val mediaItemExtras = Bundle()
mediaItemExtras.putDouble(
    MediaConstants.DESCRIPTION_EXTRAS_KEY_COMPLETION_PERCENTAGE, 0.25)
val description =
    MediaDescriptionCompat.Builder()
        .setMediaId("my-media-id")
        .setExtras(mediaItemExtras)
        // ...and any other setters.
        .build()
return MediaBrowserCompat.MediaItem(description, /* flags */)

// Elsewhere, when the user has selected MediaItem for playback.
mediaSession.setMetadata(
    MediaMetadataCompat.Builder()
        .putString(MediaMetadata.METADATA_KEY_MEDIA_ID, "my-media-id")
        // ...and any other setters.
        .build())

val playbackStateExtras = Bundle()
playbackStateExtras.putString(
    MediaConstants.PLAYBACK_STATE_EXTRAS_KEY_MEDIA_ID, "my-media-id")
mediaSession.setPlaybackState(
    PlaybackStateCompat.Builder()
        .setExtras(playbackStateExtras)
        // ...and any other setters.
        .build())

Java

import androidx.media.utils.MediaConstants;

// When the MediaItem is constructed to show in the browse view.
// Suppose the item was 25% complete when the user launched the browse view.
Bundle mediaItemExtras = new Bundle();
mediaItemExtras.putDouble(
    MediaConstants.DESCRIPTION_EXTRAS_KEY_COMPLETION_PERCENTAGE, 0.25);
MediaDescriptionCompat description =
    new MediaDescriptionCompat.Builder()
        .setMediaId("my-media-id")
        .setExtras(mediaItemExtras)
        // ...and any other setters.
        .build();
return MediaBrowserCompat.MediaItem(description, /* flags */);

// Elsewhere, when the user has selected MediaItem for playback.
mediaSession.setMetadata(
    new MediaMetadataCompat.Builder()
        .putString(MediaMetadata.METADATA_KEY_MEDIA_ID, "my-media-id")
        // ...and any other setters.
        .build());

Bundle playbackStateExtras = new Bundle();
playbackStateExtras.putString(
    MediaConstants.PLAYBACK_STATE_EXTRAS_KEY_MEDIA_ID, "my-media-id");
mediaSession.setPlaybackState(
    new PlaybackStateCompat.Builder()
        .setExtras(playbackStateExtras)
        // ...and any other setters.
        .build());

Figure 5. Playback view with a “Search results” option for viewing media items related to the user's voice search.

Your app can provide contextual search results that display to users when they initiate a search query. Android Auto and Android Automotive OS show these results through search query interfaces or through affordances that pivot on queries made earlier in the session. To learn more, see the Support voice actions section in this guide.

To display browsable search results, include the constant key BROWSER_SERVICE_EXTRAS_KEY_SEARCH_SUPPORTED in the extras bundle of your service's onGetRoot() method, mapping to the boolean true.

The following code snippet shows how to enable support in the onGetRoot() method:

Kotlin

import androidx.media.utils.MediaConstants

@Nullable
fun onGetRoot(
    @NonNull clientPackageName: String,
    clientUid: Int,
    @Nullable rootHints: Bundle
): BrowserRoot {
    val extras = Bundle()
    extras.putBoolean(
        MediaConstants.BROWSER_SERVICE_EXTRAS_KEY_SEARCH_SUPPORTED, true)
    return BrowserRoot(ROOT_ID, extras)
}

Java

import androidx.media.utils.MediaConstants;

@Nullable
@Override
public BrowserRoot onGetRoot(
    @NonNull String clientPackageName,
    int clientUid,
    @Nullable Bundle rootHints) {
    Bundle extras = new Bundle();
    extras.putBoolean(
        MediaConstants.BROWSER_SERVICE_EXTRAS_KEY_SEARCH_SUPPORTED, true);
    return new BrowserRoot(ROOT_ID, extras);
}

To start providing search results, override the onSearch() method in your media browser service. Android Auto and Android Automotive OS forward the user's search terms to this method whenever a user invokes a search query interface or “Search results” affordance.

You can organize the search results from your service's onSearch() method using title items to make them more browsable. For example, if your app plays music, you might organize search results by album, artist, and songs.

The following code snippet shows a simple implementation of the onSearch() method:

Kotlin

fun onSearch(query: String, extras: Bundle) {
  // Detach from results to unblock the caller (if a search is expensive).
  result.detach()
  object:AsyncTask() {
    internal var searchResponse:ArrayList
    internal var succeeded = false
    protected fun doInBackground(vararg params:Void):Void {
      searchResponse = ArrayList()
      if (doSearch(query, extras, searchResponse))
      {
        succeeded = true
      }
      return null
    }
    protected fun onPostExecute(param:Void) {
      if (succeeded)
      {
        // Sending an empty List informs the caller that there were no results.
        result.sendResult(searchResponse)
      }
      else
      {
        // This invokes onError() on the search callback.
        result.sendResult(null)
      }
      return null
    }
  }.execute()
}
// Populates resultsToFill with search results. Returns true on success or false on error.
private fun doSearch(
    query: String,
    extras: Bundle,
    resultsToFill: ArrayList
): Boolean {
  // Implement this method.
}

Java

@Override
public void onSearch(final String query, final Bundle extras,
                        Result<List<MediaItem>> result) {

  // Detach from results to unblock the caller (if a search is expensive).
  result.detach();

  new AsyncTask<Void, Void, Void>() {
    List<MediaItem> searchResponse;
    boolean succeeded = false;
    @Override
    protected Void doInBackground(Void... params) {
      searchResponse = new ArrayList<MediaItem>();
      if (doSearch(query, extras, searchResponse)) {
        succeeded = true;
      }
      return null;
    }

    @Override
    protected void onPostExecute(Void param) {
      if (succeeded) {
       // Sending an empty List informs the caller that there were no results.
       result.sendResult(searchResponse);
      } else {
        // This invokes onError() on the search callback.
        result.sendResult(null);
      }
    }
  }.execute()
}

/** Populates resultsToFill with search results. Returns true on success or false on error. */
private boolean doSearch(String query, Bundle extras, ArrayList<MediaItem> resultsToFill) {
    // Implement this method.
}

Custom Browse Actions

A single custom browse action.

Figure 6. Single Custom Browse Action

Custom Browse Actions allow you to add custom icons and labels to your app's MediaItem objects in the car's media app, and handle user interactions with these actions. This lets you extend the functionality of the Media App in a variety of ways, like adding "Download", "Add to Queue", "Play Radio", "Favorite", or "Remove" actions.

A custom browse actions overflow menu.

Figure 7. Custom Browse Action overflow

If there are more custom actions than the OEM allows to be displayed, an overflow menu will be presented to the user.

How do they work?

Each Custom Browse Action is defined with:

  • An Action ID (a unique string identifier)
  • An Action Label (the text displayed to the user)
  • An Action Icon URI (a vector drawable that can be tinted)

You define a list of Custom Browse Actions globally as part of your BrowseRoot. Then you can attach a subset of these actions to individual MediaItem.

When a user interacts with a Custom Browse Action, your app receives a callback in onCustomAction(). You can then handle the action and update the list of actions for the MediaItem if necessary. This is useful for stateful actions like "Favorite" and "Download". For actions that don't need updating, like "Play Radio", you don't need to update the list of actions.

Custom browse actions in a browse node root.

Figure 8. Custom Browse Action toolbar

You can also attach Custom Browse Actions to a browse node root. These actions will be displayed in a secondary toolbar under the main toolbar.

How to implement Custom Browse Actions

Here are the steps to add Custom Browse Actions to your project:

  1. Override two methods in your MediaBrowserServiceCompat implementation:
  2. Parse the action limits at runtime:
  3. Build the global list of Custom Browse Actions:
    • For each action, create a Bundle object with the following keys: * EXTRAS_KEY_CUSTOM_BROWSER_ACTION_ID: The action ID * EXTRAS_KEY_CUSTOM_BROWSER_ACTION_LABEL: The action label * EXTRAS_KEY_CUSTOM_BROWSER_ACTION_ICON_URI: The action icon URI * Add all the action Bundle objects to a list.
  4. Add the global list to your BrowseRoot:
  5. Add actions to your MediaItem objects:
    • You can add actions to individual MediaItem objects by including the list of action IDs in the MediaDescriptionCompat extras using the key DESCRIPTION_EXTRAS_KEY_CUSTOM_BROWSER_ACTION_ID_LIST. This list must be a subset of the global list of actions you defined in the BrowseRoot.
  6. Handle actions and return progress or results:

Here are some changes you can make in your BrowserServiceCompat to get started with Custom Browse Actions.

Override BrowserServiceCompat

You need to override the following methods in MediaBrowserServiceCompat. 

public void onLoadItem(String itemId, @NonNull Result<MediaBrowserCompat.MediaItem> result)
 

public void onCustomAction(@NonNull String action, Bundle extras, @NonNull Result<Bundle> result)

Parse actions limit

You should check to see how many Custom Browse Actions are supported. 

public BrowserRoot onGetRoot(@NonNull String clientPackageName, int clientUid, Bundle rootHints) {
    rootHints.getInt(
            MediaConstants.BROWSER_ROOT_HINTS_KEY_CUSTOM_BROWSER_ACTION_LIMIT, 0)
}

Build a Custom Browse Action

Each action needs to be packed into a separate Bundle.

  • Action ID 
    bundle.putString(MediaConstants.EXTRAS_KEY_CUSTOM_BROWSER_ACTION_ID,
                "<ACTION_ID>")
  • Action Label 
    bundle.putString(MediaConstants.EXTRAS_KEY_CUSTOM_BROWSER_ACTION_LABEL,
                "<ACTION_LABEL>")
  • Action Icon URI 
    bundle.putString(MediaConstants.EXTRAS_KEY_CUSTOM_BROWSER_ACTION_ICON_URI,
                "<ACTION_ICON_URI>")

Add Custom Browse Actions to Parceable ArrayList

Add all Custom Browse Action Bundle objects into an ArrayList. 

private ArrayList<Bundle> createCustomActionsList(
                                        CustomBrowseAction browseActions) {
    ArrayList<Bundle> browseActionsBundle = new ArrayList<>();
    for (CustomBrowseAction browseAction : browseActions) {
        Bundle action = new Bundle();
        action.putString(EXTRAS_KEY_CUSTOM_BROWSER_ACTION_ID,
                browseAction.mId);
        action.putString(EXTRAS_KEY_CUSTOM_BROWSER_ACTION_LABEL,
                getString(browseAction.mLabelResId));
        action.putString(EXTRAS_KEY_CUSTOM_BROWSER_ACTION_ICON_URI,
                browseAction.mIcon);
        browseActionsBundle.add(action);
    }
    return browseActionsBundle;
}

Add Custom Browse Action list to the browse root

public BrowserRoot onGetRoot(@NonNull String clientPackageName, int clientUid,
                             Bundle rootHints) {
    Bundle browserRootExtras = new Bundle();
    browserRootExtras.putParcelableArrayList(
            BROWSER_SERVICE_EXTRAS_KEY_CUSTOM_BROWSER_ACTION_ROOT_LIST,
            createCustomActionsList()));
    mRoot = new BrowserRoot(ROOT_ID, browserRootExtras);
    return mRoot;
}

Add actions to a MediaItem

MediaDescriptionCompat buildDescription (long id, String title, String subtitle,
                String description, Uri iconUri, Uri mediaUri,
                ArrayList<String> browseActionIds) {

    MediaDescriptionCompat.Builder bob = new MediaDescriptionCompat.Builder();
    bob.setMediaId(id);
    bob.setTitle(title);
    bob.setSubtitle(subtitle);
    bob.setDescription(description);
    bob.setIconUri(iconUri);
    bob.setMediaUri(mediaUri);

    Bundle extras = new Bundle();
    extras.putStringArrayList(
          DESCRIPTION_EXTRAS_KEY_CUSTOM_BROWSER_ACTION_ID_LIST,
          browseActionIds);

    bob.setExtras(extras);
    return bob.build();
}
MediaItem mediaItem = new MediaItem(buildDescription(...), flags);

Build onCustomAction result

  • Parse mediaId from Bundle extras: 
    @Override
public void onCustomAction(
          @NonNull String action, Bundle extras, @NonNull Result<Bundle> result){
  String mediaId = extras.getString(MediaConstans.EXTRAS_KEY_CUSTOM_BROWSER_ACTION_MEDIA_ITEM_ID);
}
  • For asynchronous results detach result. result.detach()
  • Build result bundle
    • Message to user 
      mResultBundle.putString(EXTRAS_KEY_CUSTOM_BROWSER_ACTION_RESULT_MESSAGE,
          mContext.getString(stringRes))
    • Update item(use to update actions in an item) 
      mResultBundle.putString(EXTRAS_KEY_CUSTOM_BROWSER_ACTION_RESULT_REFRESH_ITEM, mediaId);
    • Open Playback view 
      //Shows user the PBV without changing the playback state
mResultBundle.putString(EXTRAS_KEY_CUSTOM_BROWSER_ACTION_RESULT_SHOW_PLAYING_ITEM, null);
    • Update Browse Node 
      //Change current browse node to mediaId
mResultBundle.putString(EXTRAS_KEY_CUSTOM_BROWSER_ACTION_RESULT_BROWSE_NODE, mediaId);
  • If an error, call result.sendError(resultBundle).
  • If progress update, call result.sendProgressUpdate(resultBundle).
  • Finish by calling result.sendResult(resultBundle).

Update Action State

By using the result.sendProgressUpdate(resultBundle) method with the EXTRAS_KEY_CUSTOM_BROWSER_ACTION_RESULT_REFRESH_ITEM key, you can update the MediaItem to reflect the new state of the action. This lets you provide real-time feedback to the user about the progress and result of their action.

Example: Download Action

Here's an example of how you can use this feature to implement a download action with three states:

  1. Download: This is the initial state of the action. When the user selects this action, you can swap it with "Downloading" and call sendProgressUpdate to update the UI.
  2. Downloading: This state indicates that the download is in progress. You can use this state to show a progress bar or another indicator to the user.
  3. Downloaded: This state indicates that the download is complete. When the download finishes, you can swap "Downloading" with "Downloaded" and call sendResult with the EXTRAS_KEY_CUSTOM_BROWSER_ACTION_RESULT_REFRESH_ITEM key to indicate that the item should be refreshed. Additionally, you can use the EXTRAS_KEY_CUSTOM_BROWSER_ACTION_RESULT_MESSAGE key to display a success message to the user.

This approach lets you provide clear feedback to the user about the download process and its current state. You can add even more detail with icons to show 25%, 50%, 75% download states.

Example: Favorite Action

Another example is a favorite action with two states:

  1. Favorite: This action is displayed for items that are not in the user's favorites list. When the user selects this action, you can swap it with "Favorited" and call sendResult with the EXTRAS_KEY_CUSTOM_BROWSER_ACTION_RESULT_REFRESH_ITEM key to update the UI.
  2. Favorited: This action is displayed for items that are in the user's favorites list. When the user selects this action, you can swap it with "Favorite" and call sendResult with the EXTRAS_KEY_CUSTOM_BROWSER_ACTION_RESULT_REFRESH_ITEM key to update the UI.

This approach provides a clear and consistent way for users to manage their favorite items.

These examples showcase the flexibility of Custom Browse Actions and how you can use them to implement a variety of functionalities with real-time feedback for an enhanced user experience in the car's media app.

For a complete example implementation of this feature, you can refer to the TestMediaApp project.

Enable playback control

Android Auto and Android Automotive OS send playback control commands through your service's MediaSessionCompat. You must register a session and implement the associated callback methods.

Register a media session

In your media browser service's onCreate() method, create a MediaSessionCompat, then register the media session by calling setSessionToken().

The following code snippet shows how to create and register a media session:

Kotlin

override fun onCreate() {
    super.onCreate()
    ...
    // Start a new MediaSession.
    val session = MediaSessionCompat(this, "session tag").apply {
        // Set a callback object that implements MediaSession.Callback
        // to handle play control requests.
        setCallback(MyMediaSessionCallback())
    }
    sessionToken = session.sessionToken
    ...
}

Java

public void onCreate() {
    super.onCreate();
    ...
    // Start a new MediaSession.
    MediaSessionCompat session = new MediaSessionCompat(this, "session tag");
    setSessionToken(session.getSessionToken());

    // Set a callback object that implements MediaSession.Callback
    // to handle play control requests.
    session.setCallback(new MyMediaSessionCallback());
    ...
}

When you create the media session object, you set a callback object that is used to handle playback control requests. You create this callback object by providing an implementation of the MediaSessionCompat.Callback class for your app. The next section discusses how to implement this object.

Implement play commands

When a user requests playback for a media item from your app, Android Automotive OS and Android Auto use the MediaSessionCompat.Callback class from your app's MediaSessionCompat object that they obtained from your app's media browser service. When a user wants to control content playback, such as pausing playback or skipping to the next track, Android Auto and Android Automotive OS invoke one of the callback object's methods.

To handle content playback, your app must extend the abstract MediaSessionCompat.Callback class and implement the methods that your app supports.

Implement all the following callback methods that make sense for the type of content that your app offers:

onPrepare()
Invoked when the media source is changed. Android Automotive OS also invokes this method immediately after booting. Your media app must implement this method.
onPlay()
Invoked if the user chooses play without choosing a specific item. Your app must play its default content or, if playback was paused with onPause(), your app resumes playback.

Note: Your app should not automatically start playing music when Android Automotive OS or Android Auto connect to your media browser service. For more information, see the section about setting the initial playback state.

onPlayFromMediaId()
Invoked when the user chooses to play a specific item. The method is passed the ID that your media browser service assigned to the media item in your content hierarchy.
onPlayFromSearch()
Invoked when the user chooses to play from a search query. The app must make an appropriate choice based on the search string that was passed in.
onPause()
Invoked when the user chooses to pause playback.
onSkipToNext()
Invoked when the user chooses to skip to the next item.
onSkipToPrevious()
Invoked when the user chooses to skip to the previous item.
onStop()
Invoked when the user chooses to stop playback.

Override these methods in your app to provide any desired functionality. You don't need to implement a method if its functionality isn't supported by your app. For example, if your app plays a live stream, such as a sports broadcast, you don't need to implement the onSkipToNext() method. You can use the default implementation of onSkipToNext() instead.

Your app doesn't need any special logic to play content through the car's speakers. When your app receives a request to play content, it can play audio the same way that it plays content through a user's phone speakers or headphones. Android Auto and Android Automotive OS automatically send the audio content to the car's system to play over the car's speakers.

For more information about playing audio content, see MediaPlayer overview, Audio app overview, and the ExoPlayer overview.

Set standard playback actions

Android Auto and Android Automotive OS display playback controls based on the actions that are enabled in the PlaybackStateCompat object.

By default, your app must support the following actions:

Your app can additionally support the following actions if they are relevant to the app's content:

In addition, you have the option to create a play queue that can be displayed for the user, but it is not required. To do this, call the setQueue() and setQueueTitle() methods, enable the ACTION_SKIP_TO_QUEUE_ITEM action, and define the callback onSkipToQueueItem().

Also, add support for the Now playing icon, which is an indicator for what is currently playing. To do this, call the setActiveQueueItemId() method and pass the ID of the currently playing item in the queue. You need to update setActiveQueueItemId() whenever there is a queue change.

Android Auto and Android Automotive OS display buttons for each enabled action as well as the playback queue. When the buttons are clicked, the system invokes their corresponding callback from MediaSessionCompat.Callback.

Reserve unused space

Android Auto and Android Automotive OS reserve space in the UI for the ACTION_SKIP_TO_PREVIOUS and ACTION_SKIP_TO_NEXT actions. If your app does not support one of these functions, Android Auto and Android Automotive OS use the space to display any custom actions you create.

If you don't want to fill those spaces with custom actions, you can reserve them so that Android Auto and Android Automotive OS leave the space blank whenever your app does not support the corresponding function. To do this, call the setExtras() method with an extras bundle that contains constants that correspond to the reserved functions. SESSION_EXTRAS_KEY_SLOT_RESERVATION_SKIP_TO_NEXT corresponds to ACTION_SKIP_TO_NEXT, and SESSION_EXTRAS_KEY_SLOT_RESERVATION_SKIP_TO_PREV corresponds to ACTION_SKIP_TO_PREVIOUS. Use these constants as keys in the bundle, and use the boolean true for their values.

Set initial PlaybackState

As Android Auto and Android Automotive OS communicate with your media browser service, your media session communicates the status of content playback using the PlaybackStateCompat. Your app should not automatically start playing music when Android Automotive OS or Android Auto connect to your media browser service. Instead, rely on Android Auto and Android Automotive OS to resume or start playback based on the car's state or user actions.

To accomplish this, set the initial PlaybackStateCompat of your media session to STATE_STOPPED, STATE_PAUSED, STATE_NONE, or STATE_ERROR.

Media sessions within Android Auto and Android Automotive OS only last for the duration of the drive, so users start and stop these sessions frequently. To promote a seamless experience between drives, keep track of the user's previous session state, so that when the media app receives a resume request, the user can automatically pick up where they left off—for example, the last played media item, the PlaybackStateCompat, and the queue.

Add custom playback actions

You can add custom playback actions to display additional actions that your media app supports. If space permits (and is not reserved), Android adds the custom actions to the transport controls. Otherwise, the custom actions display in the overflow menu. Custom actions display in the order they are added to the PlaybackStateCompat.

Use custom actions to provide behavior distinct from standard actions. Don't use them to replace or duplicate standard actions.

You can add custom actions using the addCustomAction() method in the PlaybackStateCompat.Builder class.

The following code snippet shows how to add a custom “Start a radio channel” action:

Kotlin

stateBuilder.addCustomAction(
    PlaybackStateCompat.CustomAction.Builder(
        CUSTOM_ACTION_START_RADIO_FROM_MEDIA,
        resources.getString(R.string.start_radio_from_media),
        startRadioFromMediaIcon
    ).run {
        setExtras(customActionExtras)
        build()
    }
)

Java

stateBuilder.addCustomAction(
    new PlaybackStateCompat.CustomAction.Builder(
        CUSTOM_ACTION_START_RADIO_FROM_MEDIA,
        resources.getString(R.string.start_radio_from_media),
        startRadioFromMediaIcon)
    .setExtras(customActionExtras)
    .build());

For a more detailed example of this method, see the setCustomAction() method in the Universal Android Music Player sample app on GitHub.

After creating your custom action, your media session can respond to the action by overriding the onCustomAction() method.

The following code snippet shows how your app might respond to a “Start a radio channel” action:

Kotlin

override fun onCustomAction(action: String, extras: Bundle?) {
    when(action) {
        CUSTOM_ACTION_START_RADIO_FROM_MEDIA -> {
            ...
        }
    }
}

Java

@Override
public void onCustomAction(@NonNull String action, Bundle extras) {
    if (CUSTOM_ACTION_START_RADIO_FROM_MEDIA.equals(action)) {
        ...
    }
}

For a more detailed example of this method, see the onCustomAction method in the Universal Android Music Player sample app on GitHub.

Icons for custom actions

Each custom action that you create requires an icon resource. Apps in cars can run on many different screen sizes and densities, so icons that you provide must be vector drawables. A vector drawable allows you to scale assets without losing the detail. A vector drawable also makes it easy to align edges and corners to pixel boundaries at smaller resolutions.

If a custom action is stateful—for example, it toggles a playback setting on or off—provide different icons for the different states, so users can see a change when they select the action.

Provide alternative icon styles for disabled actions

When a custom action is unavailable for the current context, swap the custom action icon with an alternative icon that shows that the action is disabled.

Figure 6. Samples of off-style custom action icons.

Indicate audio format

To indicate that currently playing media uses a special audio format, you can specify icons that are rendered in cars that support this feature. You can set the KEY_CONTENT_FORMAT_TINTABLE_LARGE_ICON_URI and the KEY_CONTENT_FORMAT_TINTABLE_SMALL_ICON_URI in the extras bundle of the currently playing media item (passed to MediaSession.setMetadata()). Make sure to set both of those extras, to accommodate different layouts.

In addition, you can set the KEY_IMMERSIVE_AUDIO extra to tell car OEMs that this is immersive audio, and they should be very careful when deciding whether to apply audio effects that might interfere with the immersive content.

You can configure the currently-playing media item so its subtitle, description, or both are links to other media items. That lets the user jump quickly to related items; for example, they might jump to other songs by the same artist, other episodes of that podcast, etc. If the car supports this feature, users can tap the link to browse to that content.

To add links, configure the KEY_SUBTITLE_LINK_MEDIA_ID metadata (to link from the subtitle) or KEY_DESCRIPTION_LINK_MEDIA_ID (to link from the description). For details, see the reference documentation for those metadata fields.

Support voice actions

Your media app must support voice actions to help provide drivers with a safe and convenient experience that minimizes distractions. For example, if your app is playing one media item, the user can say “Play [song title]" to tell your app to play a different song without looking at or touching the car's display. Users can initiate queries by clicking the appropriate buttons on their steering wheel or speaking the hotwords "OK Google."

When Android Auto or Android Automotive OS detects and interprets a voice action, that voice action is delivered to the app through onPlayFromSearch(). On receiving this callback, the app finds content matching the query string and starts playback.

Users can specify different categories of terms in their query: genre, artist, album, song name, radio station, or playlist, among others. When building support for search, account for all the categories that make sense for your app. If Android Auto or Android Automotive OS detects that a given query fits into certain categories, it appends extras in the extras parameter. The following extras can be sent:

Account for an empty query string, which can be sent by Android Auto or Android Automotive OS if the user doesn't specify search terms. For example, if the user says "Play some music." In that case, your app might choose to start a recently played or newly suggested track.

If a search cannot be processed quickly, do not block in onPlayFromSearch(). Instead, set the playback state to STATE_CONNECTING and perform the search on an async thread.

Once playback begins, consider populating the media session's queue with related content. For example, if the user requests an album to be played, your app might fill the queue with the album's tracklist. Also consider implementing support for browsable search results so a user can choose a different track that matches their query.

In addition to "play" queries, Android Auto and Android Automotive OS recognize voice queries to control playback like "pause music" and "next song" and match these commands to the appropriate media session callbacks, like onPause() and onSkipToNext().

For a detailed example on how to implement voice-enabled playback actions in your app, see Google Assistant and media apps.

Implement distraction safeguards

Because a user's phone is connected to their car's speakers while using Android Auto, you must take additional precautions to help prevent driver distraction.

Suppress alarms in the car

Android Auto media apps must not start playing audio through the car speakers unless the user starts playback by, for example, pressing a play button. Even a user-scheduled alarm from your media app must not start playing music through the car speakers.

To fulfill this requirement, your app can use CarConnection as a signal before playing any audio. Your app can check whether the phone is projecting to a car screen by observing the LiveData for the car connection type and checking whether it is equal to CONNECTION_TYPE_PROJECTION.

If the user's phone is projecting, media apps that support alarms must do one of the following things:

  • Disable the alarm.
  • Play the alarm over STREAM_ALARM and provide a UI on the phone screen to disable the alarm.

Handle media advertisements

By default, Android Auto displays a notification when the media metadata changes during an audio playback session. When a media app switches from playing music to running an advertisement, it is distracting to display a notification to the user. To prevent Android Auto from displaying a notification in this case, you must set the media metadata key METADATA_KEY_IS_ADVERTISEMENT to METADATA_VALUE_ATTRIBUTE_PRESENT, as shown in the following code snippet:

Kotlin

import androidx.media.utils.MediaConstants

override fun onPlayFromMediaId(mediaId: String, extras: Bundle?) {
    MediaMetadataCompat.Builder().apply {
        if (isAd(mediaId)) {
            putLong(
                MediaConstants.METADATA_KEY_IS_ADVERTISEMENT,
                MediaConstants.METADATA_VALUE_ATTRIBUTE_PRESENT)
        }
        // ...add any other properties you normally would.
        mediaSession.setMetadata(build())
    }
}

Java

import androidx.media.utils.MediaConstants;

@Override
public void onPlayFromMediaId(String mediaId, Bundle extras) {
    MediaMetadataCompat.Builder builder = new MediaMetadataCompat.Builder();
    if (isAd(mediaId)) {
        builder.putLong(
            MediaConstants.METADATA_KEY_IS_ADVERTISEMENT,
            MediaConstants.METADATA_VALUE_ATTRIBUTE_PRESENT);
    }
    // ...add any other properties you normally would.
    mediaSession.setMetadata(builder.build());
}

Handle general errors

When the app experiences an error, set the playback state to STATE_ERROR and provide an error message using the setErrorMessage() method. See PlaybackStateCompat for a list of error codes that you can use when setting the error message. Error messages must be user-facing and localized with the user's current locale. Android Auto and Android Automotive OS can then display the error message to the user.

For example, if content is not available in the user's current region, you can use the ERROR_CODE_NOT_AVAILABLE_IN_REGION error code when setting the error message.

Kotlin

mediaSession.setPlaybackState(
    PlaybackStateCompat.Builder()
        .setState(PlaybackStateCompat.STATE_ERROR)
        .setErrorMessage(PlaybackStateCompat.ERROR_CODE_NOT_AVAILABLE_IN_REGION, getString(R.string.error_unsupported_region))
        // ...and any other setters.
        .build())

Java

mediaSession.setPlaybackState(
    new PlaybackStateCompat.Builder()
        .setState(PlaybackStateCompat.STATE_ERROR)
        .setErrorMessage(PlaybackStateCompat.ERROR_CODE_NOT_AVAILABLE_IN_REGION, getString(R.string.error_unsupported_region))
        // ...and any other setters.
        .build());

For more information about error states, see Using a media session: States and errors.

If an Android Auto user needs to open your phone app to resolve an error, provide that information to the user in your message. For example, your error message might say "Sign in to [your app name]" instead of "Please sign in."

Other resources

Next
Add support for Android Auto