Ios 如何显示缩略图

如何在播放前显示视频的缩略图。这是一个简单的问题，我是这个领域的新手，有人能帮我解决这个问题吗

NSString *str11 = [NSString stringWithFormat:@"https://www.youtube.com/embed/XGSy3_Czz8k?autoplay=1"];  

NSURL *url1 = [NSURL URLWithString:str11];

MPMoviePlayerController *player = [[MPMoviePlayerController alloc] initWithContentURL:url1] ;
                [player play];

AVAsset *asset = [AVAsset assetWithURL:url1];

AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc]initWithAsset:asset];

CMTime time = CMTimeMake(1, 1);
CGImageRef imageRef = [imageGenerator copyCGImageAtTime:time actualTime:NULL error:NULL];
UIImage *thumbnail = [UIImage imageWithCGImage:imageRef];
NSLog(@"thumbmail %@",thumbnail);

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如果不需要使用MPMoviewPlayer，则可以使用UIWebView。在那里，您将自动加载预览缩略图

 [self.webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"https://www.youtube.com/embed/XGSy3_Czz8k?autoplay=1"]]];