asp.net video upload with progress bar

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ASP.NET

jQuery

I am trying to implement a video upload with a progress bar using an XMLhttprequest() and a html5 progress element like this:

<input type="file" name="fileUpload1" id="fu1" />
<button type="button" id="clicker" value="Upload" name="Upload" >Upload</button>
<progress id="prog1"></progress>

and the js:

$("#clicker").live('click', function (e) {
     e.preventDefault();
     UploadVideo("fu1", "");
 });

 function UploadVideo(elm, url) {
      var xhr = new XMLHttpRequest();
      var fd = new FormData();
      fd.append("fu1", document.getElementById("fu1").files[0]);
      xhr.addEventListener("progress", ProcessVideo, false);
      xhr.open("POST", "Handler.ashx");
      xhr.send(fd);
 }

 function ProcessVideo(evt) {
     if (evt.lengthComputable) {
         var prog = document.getElementById("prog1");
         prog.max = evt.total;
         prog.value = evt.loaded;
     }
 }

finally i am handling it using this generic ashx handler:

public void ProcessRequest (HttpContext context) {
     var file = context.Request.Files["fu1"];
     var savePath = HttpContext.Current.Server.MapPath("~/teees/" + file.FileName);
     file.SaveAs(savePath);
     context.Response.ContentType = "text/plain";
     context.Response.Write("Hello World");
}

this works fine but the progress bar doesn't move its stuck at zero then jumps to 100 when the upload is finished, what is the problem ?

thanks