找不到AVAssetExportSession outputFileType的正确值

Question

我正在使用以下内容：

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
     if info[UIImagePickerControllerMediaType] as? String == "public.movie" {
        // here your video capture code
        let videoURL = info[UIImagePickerControllerMediaURL] as! NSURL!
        let data = NSData(contentsOf: videoURL! as URL)!
        print("File size before compression: \(Double(data.length / 1048576)) mb")
        let compressedURL = NSURL.fileURL(withPath: NSTemporaryDirectory() + NSUUID().uuidString + ".m4v")
        compressVideo(inputURL: videoURL as! URL, outputURL: compressedURL) { (exportSession) in
                guard let session = exportSession else {
                    return
                }

                switch session.status {
                case .unknown:
                    break
                case .waiting:
                    break
                case .exporting:
                    break
                case .completed:
                    guard let compressedData = NSData(contentsOf: compressedURL) else {
                        return
                    }
                   print("File size after compression: \(Double(compressedData.length / 1048576)) mb")
                case .failed:
                    break
                case .cancelled:
                    break
                }
            }
       }
       self.dismiss(animated: true, completion: nil)
 }

 func compressVideo(inputURL: URL, outputURL: URL, handler:@escaping (_ exportSession: AVAssetExportSession?)-> Void) {
        let urlAsset = AVURLAsset(url: inputURL, options: nil)
        guard let exportSession = AVAssetExportSession(asset: urlAsset, presetName: AVAssetExportPresetLowQuality) else {
            handler(nil)

            return
        }

        exportSession.outputURL = outputURL
        exportSession.outputFileType = AVFileTypeQuickTimeMovie
        exportSession.shouldOptimizeForNetworkUse = true
        exportSession.exportAsynchronously { () -> Void in
            handler(exportSession)
        }
    }

我收到以下错误消息：Use of unresolved identifier 'AVFileTypeQuickTimeMovie'，并且找不到从任何地方获取相同实例的方法。请帮助我纠正此问题。我正在使用Swift 4.1，也许名称在Swift 4.1中已经更改。