Android
AudioManager

Solicitud de enfoque de audio transitorio

audioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);

audioManager.requestAudioFocus(audioListener, AudioManager.STREAM_MUSIC, AudioManager.AUDIOFOCUS_GAIN_TRANSIENT);

changedListener = new AudioManager.OnAudioFocusChangeListener() {
    @Override
    public void onAudioFocusChange(int focusChange) {
        if (focusChange == AudioManager.AUDIOFOCUS_GAIN) {
            // You now have the audio focus and may play sound.
            // When the sound has been played you give the focus back.
            audioManager.abandonAudioFocus(changedListener);
        }
    }
}

Solicitando Audio Focus

audioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);

audioManager.requestAudioFocus(audioListener, AudioManager.STREAM_MUSIC, AudioManager.AUDIOFOCUS_GAIN);

changedListener = new AudioManager.OnAudioFocusChangeListener() {
    @Override
    public void onAudioFocusChange(int focusChange) {
        if (focusChange == AudioManager.AUDIOFOCUS_GAIN) {
            // You now have the audio focus and may play sound.
        }
        else if (focusChange == AudioManager.AUDIOFOCUS_REQUEST_FAILED) {
            // Handle the failure.
        }
    }
}