動画のダウンローダー(ネイキッドの場合)

       var client = new HttpClient();
        var video = client.GetAsync(動画のURL);

        var h = video.Result.Content.ReadAsByteArrayAsync();

        using(var fs = new FileStream("test.mp4", FileMode.Create, FileAccess.Write))
        {
            fs.Write(h.Result, 0, h.Result.Length);
        }