在创建AVAssetDownloadURLSession之前，需要在AppDelegate中设置NSURLSessionConfiguration并创建URLSession。以下是示例代码：

在AppDelegate中：

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool { let backgroundConfiguration = URLSessionConfiguration.background(withIdentifier: "yourIdentifer") backgroundConfiguration.sessionSendsLaunchEvents = true

let downloadSession = URLSession(configuration: backgroundConfiguration, delegate: self, delegateQueue: OperationQueue.main)
downloadSession.getTasksWithCompletionHandler { (dataTasks, uploadTasks, downloadTasks) in
    for downloadTask in downloadTasks {
        downloadTask.cancel()
    }
}
downloadSession.finishTasksAndInvalidate()
return true

}

在ViewController中：

let urlAsset = AVURLAsset(url: videoURL) let downloadTask = downloadSession.makeAssetDownloadTask(asset: urlAsset, assetTitle: "title", assetArtworkData: nil, options: nil) downloadTask?.resume()

注意：此代码在Swift 5.0上测试通过。如果使用的是其他版本的Swift，请确认代码是否适用。