public boolean isPlaying() {
        return mAudioTrack.getPlayState() == AudioTrack.PLAYSTATE_PLAYING;
    }
Returns the current PTS of the playback head or PTS_NOT_SET if the PTS cannot be reliably
calculated yet.
For this method to return a PTS, audio samples need to be written before ({@link #write(ByteBuffer, long)}.
@return the PTS at the playback head or PTS_NOT_SET if unknown
MediaPlayer/src/main/java/net/protyposis/android/mediaplayer/AudioPlayback.java