下载的视频无法播放iOS

Question

在我的iOS应用程序中，我向Java Servlet发送一个GET请求，该请求成功地向我发送了一个.mp4视频。我正在使用NSURLSession API，我想在完成块中播放视频，但视频从不播放。我没有看到我的代码有什么问题：

@interface ViewVideoViewController ()

@property (nonatomic) NSURLSession *session;
@property (nonatomic, strong) MPMoviePlayerController *player;

@end

@implementation ViewVideoViewController

- (void)viewDidLoad {
[super viewDidLoad];

NSString *requestedURL=[NSString stringWithFormat:@"http://urlservlet.com?filename=%@", self.filename];
NSURL *url = [NSURL URLWithString:requestedURL];

NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
[request setCachePolicy:NSURLRequestReloadIgnoringLocalCacheData];
[request setHTTPShouldHandleCookies:NO];
[request setTimeoutInterval:30];
[request setHTTPMethod:@"GET"];
[request setURL:url];

NSURLSessionConfiguration *config =
[NSURLSessionConfiguration defaultSessionConfiguration];
self.session = [NSURLSession sessionWithConfiguration:config
                                             delegate:nil
                                        delegateQueue:nil];
NSURLSessionDownloadTask *downloadTask = [self.session downloadTaskWithRequest:request completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error) {
    NSData *downloadedData = [NSData dataWithContentsOfURL:location
                                                   options:kNilOptions
                                                     error:nil];


    NSLog(@"Video size: %lu", (unsigned long)downloadedData.length);//the result is good so the video is here
    self.player = [[MPMoviePlayerController alloc] initWithContentURL:location];
    UIView *view = self.player.view;
    view.frame = CGRectMake(16, 84, 288, 128);
    [self.view addSubview:view];
    [self.player prepareToPlay];
    [self.player play];
}];
[downloadTask resume];

}
@end