iOS VAST XML Parser

Question

我遇到的问题是如何在Objective-C中播放VAST视频格式？我试过这段代码：

NSURL *url = [NSURL URLWithString:@"http://ad3.liverail.com/?LR_PUBLISHER_ID=1331&LR_CAMPAIGN_ID=229&LR_SCHEMA=vast3"];
player.movieSourceType =MPMovieSourceTypeStreaming;

MPMoviePlayerController *controller = [[MPMoviePlayerController alloc] initWithContentURL:url];
[player prepareToPlay];
self.myPlayer = controller; //Super important
controller.view.frame = self.view.bounds; //Set the size

[self.view addSubview:controller.view]; //Show the view
[controller play]; //Start playing

但我只见过黑屏。在我看来，我必须解析这些链接，但我不能这样做。我们如何使用Apple框架解析VAST XML解析器，而不是第三方库？