Optimizing Media Playback for Android Auto and Mobile Devices

Introduction

In modern app development, providing a seamless media playback experience across various platforms—including Android Auto and mobile devices—is crucial. However, developers often encounter issues where media playback works correctly on Android Auto but fails on mobile devices. This article explores common causes of such discrepancies and provides solutions to ensure a consistent experience.

Understanding Media Session and Media Items

Android Auto relies on MediaSession and MediaLibrarySession to interact with a media service. When a user selects a media item, the onAddMediaItems() method is triggered to process the request. If media playback fails only on mobile devices, the root cause typically lies in how media items are constructed and passed.

Common Issues in Mobile Playback

1. Empty or Null Media Items in onAddMediaItems()

When the onAddMediaItems() method receives an empty or null list, Android Auto might still function correctly because of internal caching or behavior differences. However, mobile playback might fail due to missing or incorrectly built media items.

Solution: Add extensive logging to debug what media items are being received and processed.

override fun onAddMediaItems(
    mediaSession: MediaSession,
    controller: MediaSession.ControllerInfo,
    mediaItems: MutableList<MediaItem>
): ListenableFuture<List<MediaItem>> {

    if (mediaItems.isEmpty()) {
        Log.d("onAddMediaItems", "ERROR: mediaItems is EMPTY on MOBILE!")
        return Futures.immediateFuture(emptyList())
    }

    val updatedMediaItems = mediaItems.mapNotNull { mediaItem ->
        Log.d("onAddMediaItems", "Processing media item ID: ${mediaItem.mediaId}")

        val currentStation = MediaData.stations.find { it.uuid == mediaItem.mediaId }
        val currentPlaylist = MediaData.playlists.find { it.id.toString() == mediaItem.mediaId }

        val uri = currentStation?.getStreamUri() ?: currentPlaylist?.urlStream
        
        if (uri == null) {
            Log.d("onAddMediaItems", "ERROR: No valid URI found for ${mediaItem.mediaId} on MOBILE")
            return@mapNotNull null
        }

        MediaItem.Builder()
            .setUri(uri.toUri())
            .setMediaId(mediaItem.mediaId)
            .setMediaMetadata(
                mediaItem.mediaMetadata.buildUpon()
                    .setIsBrowsable(false)
                    .setIsPlayable(true)
                    .setTitle(currentPlaylist?.title ?: currentStation?.name)
                    .build()
            )
            .build()
    }
    return Futures.immediateFuture(updatedMediaItems)
}

2. Incorrect MediaItem Configuration in onGetChildren()

Android Auto and mobile devices rely on onGetChildren() to retrieve the available media items. If the method does not correctly mark media items as playable, Android Auto might still function, but mobile playback could fail.

Solution: Ensure media items are properly constructed.

private fun createMediaItem(id: String, title: String, url: String): MediaItem {
    return MediaItem.Builder()
        .setMediaId(id)
        .setUri(Uri.parse(url))
        .setMediaMetadata(
            MediaMetadata.Builder()
                .setTitle(title)
                .setIsBrowsable(false)
                .setIsPlayable(true)
                .build()
        )
        .build()
}

3. ExoPlayer Not Handling Playback Properly

If media items are correctly passed but playback fails on mobile devices, the issue may reside in how ExoPlayer is handling the media item. Logging ExoPlayer events can help diagnose playback issues.

Solution: Ensure ExoPlayer is correctly initialized and debug playback errors.

private fun initializePlayer() {
    val exoPlayer: ExoPlayer = ExoPlayer.Builder(this).build()
    
    exoPlayer.addListener(object : Player.Listener {
        override fun onPlayerError(error: PlaybackException) {
            Log.d("PlayerService", "Playback error: ${error.errorCodeName}")
        }

        override fun onIsPlayingChanged(isPlaying: Boolean) {
            Log.d("PlayerService", "Is Playing: $isPlaying")
        }
    })

    player = exoPlayer
}

Final Debugging Steps

To pinpoint the exact issue, follow these steps:

1. Check logs from onAddMediaItems() to ensure media items are correctly retrieved.
2. Verify onGetChildren() is returning playable media items.
3. Manually set a test media item in onAddMediaItems() to confirm ExoPlayer playback.
4. Inspect ExoPlayer logs for playback errors.

Conclusion

Ensuring seamless media playback across Android Auto and mobile devices requires correctly handling MediaSession, MediaItems, and ExoPlayer configurations. By applying the debugging strategies outlined above, developers can resolve discrepancies between platforms and enhance user experience.