code: private void resume() {
          if (mIsPaused) {
              mIsPaused = false;
              mIsPausedAfterAudioFocusChanged = false;
              // Try to gain the audio focus before preparing and starting the media player.
              if (mAudioManager.requestAudioFocus(this, AudioManager.STREAM_MUSIC, AudioManager.AUDIOFOCUS_GAIN)
                      == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
                  mMediaPlayer.start();
  
                  Intent intent = new Intent(PlaybackListener.ACTION_ON_TRACK_PLAYED);
                  intent.putExtra(PlaybackListener.EXTRA_KEY_TRACK,
                          mPlayerPlaylist.getCurrentTrack());
                  mLocalBroadcastManager.sendBroadcast(intent);
  
                  updateNotification();
                  mMediaSession.setPlaybackState(MediaSessionWrapper.PLAYBACK_STATE_PLAYING);
                  resumeTimer();
              }
          }
      }
docs: Resume the playback.