下载视频不起作用，流式传输

The code:

WebClient webClient = new WebClient();
webClient.DownloadProgressChanged += t_ProgressChanged;
webClient.DownloadFileAsync(new Uri("https://cdn3.streamcloud.eu:8080/6hv75ivjnkoax3ptx3silq7q6hn4jq324yv5gophqq4eq7fqqglgw5kneq/video.mp4"), @"c:\video.mp4");
WebClient webClient = new WebClient