I’m developing an Android Auto app and trying to play an MP3 file stored in res/raw through the vehicle’s audio system. However, the sound is played on the mobile device instead. Library-managed sounds play correctly through the car’s speakers.

I used MediaPlayer and AudioManager to manage playback and audio focus (code below). I expected the audio to play through the vehicle’s speakers, similar to other system sounds, but it only plays through the mobile device. I am seeking advice on whether my implementation is incorrect or if additional configurations are necessary for Android Auto.

class HelloWorldScreen(carContext: CarContext) : Screen(carContext) {
    private lateinit var mediaPlayer: MediaPlayer
    private lateinit var audioManager: AudioManager
    private lateinit var audioFocusChangeListener: AudioManager.OnAudioFocusChangeListener

    init {
        lifecycle.addObserver(object : DefaultLifecycleObserver {
            override fun onCreate(owner: LifecycleOwner) {
                audioManager = carContext.getSystemService(Context.AUDIO_SERVICE) as AudioManager
                setupAudioFocusChangeListener()
                setupMediaPlayer()
            }

            override fun onDestroy(owner: LifecycleOwner) {
                super.onDestroy(owner)
                mediaPlayer.release()
                audioManager.abandonAudioFocus(audioFocusChangeListener)
            }
        })
    }

    private fun setupMediaPlayer() {
        mediaPlayer = MediaPlayer.create(carContext, R.raw.announce)
        mediaPlayer.setOnCompletionListener {
            audioManager.abandonAudioFocus(audioFocusChangeListener)
        }
    }

    private fun setupAudioFocusChangeListener() {
        audioFocusChangeListener = AudioManager.OnAudioFocusChangeListener { focusChange ->
            when (focusChange) {
                AudioManager.AUDIOFOCUS_LOSS -> mediaPlayer.pause()
            }
        }
    }

    private fun requestAudioFocus(): Boolean {
        val result = audioManager.requestAudioFocus(
            audioFocusChangeListener,
            AudioManager.STREAM_NOTIFICATION,
            AudioManager.AUDIOFOCUS_GAIN_TRANSIENT
        )
        return result == AudioManager.AUDIOFOCUS_REQUEST_GRANTED
    }


    override fun onGetTemplate(): Template {
        val row = Row.Builder().setTitle("Hello AndroidX!").build()
        return PaneTemplate.Builder(Pane.Builder().addRow(row).build())
            .setHeaderAction(Action.APP_ICON)
            .setActionStrip(
                ActionStrip.Builder()
                    .addAction(
                        Action.Builder()
                            .setTitle("Play")
                            .setOnClickListener { buttonAction() }
                            .build())
                    .build())
            .build()
    }
    
    private fun buttonAction() {
        if (requestAudioFocus()) {
            mediaPlayer.start()
        }
    }
}