Playing music with Sprite Kit

music.m

-(void) loadSound {
    NSError *error;
    NSURL * backgroundMusicURL = [[NSBundle mainBundle] URLForResource:@"otto_basetrack" withExtension:@"mp3"];
    backgroundMusicPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:backgroundMusicURL error:&error];
    backgroundMusicPlayer.numberOfLoops = -1;
    [backgroundMusicPlayer prepareToPlay];
    [backgroundMusicPlayer play];
}