NewMusicPlayer(&_mPlayer);
    MusicPlayerPreroll(_mPlayer);
    MusicSequence mSequence; NewMusicSequence(&mSequence);

    OSErr err = MusicSequenceFileLoad(
                mSequence, (__bridge CFURLRef)playTrackURL,
                kMusicSequenceFile_iMelodyType, 0); // likely problem here

    if (err) {
        NSLog(@"sequence %hd", err); // sequence -10871
    }

    MusicPlayerSetSequence(_mPlayer, mSequence);
    MusicPlayerSetPlayRateScalar(_mPlayer, 1.0);

    err = MusicPlayerStart(_mPlayer);

    if (err) {
        NSLog(@"player %hd", err); // player -10852
    }