Asynchronous Task controllers in C#4 - c#-4.0

Question

I want to write an asynchronous Controller that is displaying in output an IEnumerable<IEnumerable<Video>>
I don't know I can manage to write correctly my function Task<IEnumerable<IEnumerable<Video>>> GetVideosAsync(xxxxx) especially the Task.ContinueWhenAll function (in order not to have blocking code ).
Is it better to use a lambda for this piece of code ...?
Can someone help me ?
Nb: *I can only use C#4 and visual Studio 2010
public class HomeController : AsyncController
{
string[] sources = {
"http://xxxx/membervideos/1",
"http://xxxx/membervideos/2"
};
public Task<ActionResult> Async()
{
var sw = Stopwatch.StartNew();
var data = GetVideosAsync();
sw.Stop();
ViewBag.Elapsed = sw.ElapsedMilliseconds;
return View("~/views/home/index.cshtml", data);
}
Task<IEnumerable<IEnumerable<Video>>> GetVideosAsync()
{
var allVideosTasks = new List<Task<IEnumerable<Video>>>();
foreach (var url in sources)
{
allVideosTasks.Add(DownloadDataAsync(url));
}
var context = TaskScheduler.FromCurrentSynchronizationContext();
Task.Factory.ContinueWhenAll<IEnumerable<Video>,IEnumerable<IEnumerable<Video>>(
/// CODE TO ComplETE HERE
);
Task<IEnumerable<Video>> DownloadDataAsync(string url)
{
var httpClient = new HttpClient();
var httpResponseMessage = httpClient.GetAsync(url);
var result = httpResponseMessage.ContinueWith
(t =>
{
t.Result.EnsureSuccessStatusCode();
return t.Result.Content.ReadAsAsync<IEnumerable<Video>>();
}
).Unwrap();
return result;
}
/**** VIEW ******/
#{
ViewBag.Title = "Home Page";
}
#model IEnumerable<IEnumerable<MvcApplication1.Models.Video>>
<table>
#foreach (var memberVideos in Model)
{
<tr>
#foreach(var video in memberVideos){
<td>
<div>#video.Title</div>
<div><img src="http://xxxxxx/membervideos/#video.ImageUrl" style="width: 185px;"/> </div>
</td>
}
</tr>
}
</table>
<h1>#ViewBag.Elapsed</h1>