AVPlayer无法播放我解析的视频

我正在尝试从解析服务器播放视频 我的视频播放器是空的 当我打印url时,我会得到正确的视频url

let thevideo:PFFile! = (self.selectedmsg["file"] as! PFFile)
            let url:NSURL = NSURL(string: thevideo.url!)!
            let player = AVPlayer(URL: url)

            let playercontroller = AVPlayerViewController()
            playercontroller.player = player

            self.presentViewController(playercontroller, animated: true) {

                player.play()
            }

有什么帮助吗?