How to make background worker as async await in windows phone 8?

Hi,

I am using background worker for uploading videos with queue.

From the Queuelist I am uploading videos one by one but in background worker dowork event I am calling async await method but event it is not completing the task it is going for background worker completed event.

In the completed event I am deleting completed video and start uploading next one.But dowork method is not awaitable.

Here is my sample code:

 void bgWorkerVideoQueue_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            if (videoQueue != null && videoQueue.Count > 0)
                bgWorkerVideoQueue.RunWorkerAsync();
        }
        async void bgWorkerVideoQueue_DoWork(object sender, DoWorkEventArgs e)
        {           
            if (videoQueue != null && videoQueue.Count > 0)
            {
                var res = await SaveVideoToServer(videoQueue[0]);               
            }
         }
        private async Task<string> SendVideosQueueToServer(string videoName)
        {
            var tcs = new TaskCompletionSource<string>();
            if (videoQueue != null && videoQueue.Count > 0)
            {
                var res = await SaveVideoToServer(videoName);
                tcs.SetResult(res);
               //here removing completed video from quelist
            }
            return await tcs.Task;
        }

How can I resolve this issue.

Anybody can help me, is very appreciable.

Thanks in advance.