为什么MPMoviePlayerController在电影结束后阻止恢复音频?

AVAudioPlayer ,并在特定情况下,使用 MPMoviePlayerController . 为了一次只能播放一首曲目,我在启动视频之前停止背景音乐:

-(void)startVideo{
    [backgroundMusic stop];
    MPMoviePlayerViewController *mp = [[MPMoviePlayerViewController alloc] initWithContentURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"videofile" ofType:@"m4v"]]];
    [self presentMoviePlayerViewControllerAnimated:mp];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(videoOver) name:MPMoviePlayerPlaybackDidFinishNotification object:nil];
    [mp.moviePlayer play];
    [mp release];
}

-(void)videoOver{
    [[NSNotificationCenter defaultCenter] removeObserver:self name:MPMoviePlayerPlaybackDidFinishNotification object:nil];
    if(![backgroundMusic play]){
         NSLog(@"bad: can't resume bg music!");
         [backgroundMusic release];
         backgroundMusic = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"videofile" ofType:@"m4v"]] error:NULL];
         backgroundMusic.delegate = self; 
         backgroundMusic.numberOfLoops = -1; 
         [backgroundMusic play];
    }
}

恢复工作进行得很好,没有重新创建 对象(即 play 玩