由于视频损坏，AVAsset无法导入。错误捕捉？

Question

我使用AVFoundation合并了视频，并发现了一个似乎有时间刻度损坏的视频。该视频在点击＆＃34;选择＆＃34;时会产生错误。在UIImagePickerController。一旦＆＃34;选择＆＃34;系统错误就会打印出来。按钮被点击，但是应用程序崩溃直到下面的注释行才会发生。崩溃发生在加载无法加载的资产时，因为它是零值。

如何捕获此错误以通知用户该问题并防止崩溃？

  

2017-07-31 14:22:18.284542-0500 APP [2299：62163] [Generic]视频导出资产失败：错误Domain = AVFoundationErrorDomain Code = -11821＆＃34;无法解码＆＃34; UserInfo = {NSLocalizedDescription =无法解码，NSLocalizedFailureReason =媒体数据无法解码。它可能已损坏。}

   extension videoViewController: UIImagePickerControllerDelegate {
func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
    let mediaType = info[UIImagePickerControllerMediaType] as! NSString
    dismiss(animated: true, completion: nil)
    let mediaInfo = info

    print("Media Info: ", mediaInfo)

    if mediaType == kUTTypeMovie {
//ERROR THROWS AT BELOW LINE
        let avAsset = AVAsset(url:info[UIImagePickerControllerMediaURL] as! URL)
        //var message = ""
        if loadingAssetOne {
            //message = "Video one loaded"
            firstAsset = avAsset
        } else {
            //message = "Video two loaded"
            secondAsset = avAsset
            //set bg image

            videoPreviewUIImage(assetName: avAsset as! AVURLAsset)
        }
        //let alert = UIAlertController(title: "Asset Loaded", message: message, preferredStyle: .alert)
        //alert.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.cancel, handler: nil))
        //present(alert, animated: true, completion: nil)
    }
    }

}