NSString *urlPath;
    NSURL *videoUrl;

    urlPath = [[NSBundle mainBundle] pathForResource:@"fogLoop" ofType:@"mp4"];
    videoUrl = [NSURL fileURLWithPath:urlPath];

    avPlayer = [AVPlayer playerWithURL:videoUrl];
    avPlayerLayer = [AVPlayerLayer playerLayerWithPlayer:avPlayer];

    avPlayerLayer.frame = videoView.layer.bounds;

    avPlayerLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;

    [videoView.layer addSublayer: avPlayerLayer];

    avPlayer.actionAtItemEnd = AVPlayerActionAtItemEndNone;

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(playerItemDidReachEnd:)
                                                 name:AVPlayerItemDidPlayToEndTimeNotification
                                               object:[avPlayer currentItem]];

    [avPlayer play];

我在这个视图上有几个UILabel.我只想把视频作为背景元素.使用此代码,它似乎可以播放所有UI元素.如何让它去后台？