let documentsUrl = FileManager.default.urls(for: .documentDirectory, in: FileManager.SearchPathDomainMask.userDomainMask).first
let fileUrl = documentsUrl?.appendingPathComponent(response.suggestedFilename!)
print(fileManager.fileExists(atPath: (fileUrl?.absoluteString)!))
//然而Swift检查不了视频是否存在.