accept: {
title: 'Images',
extensions: 'gif,jpg,jpeg,bmp,png',
mimeTypes: 'image/*'
}

[HttpPost]
public ActionResult upload(HttpPostedFileBase file)
{
if (file != null && file.ContentLength > 0)
{
string folderpath = "/UploadFile/";//上传图片的文件夹
if (!Directory.Exists(folderpath))
{
Directory.CreateDirectory(Server.MapPath(folderpath));
}
string ext1 = Path.GetExtension(file.FileName);
if (ext1 != ".mp4" && ext1 != ".rmvb" && ext1 != ".avi" && ext1 != ".flv")//笔者这儿修改了后缀的判断
{
return Json(new { statu = 201, msg = "文件格式不正确！" });
}
else
{
string name = DateTime.Now.ToString("yyyyMMddHHmmssff");
string ext = Path.GetExtension(file.FileName);
string downpath = folderpath + name + ext;
string filepath = Server.MapPath(folderpath) + name + ext;
file.SaveAs(filepath);
return Json(new { statu = 200, src = downpath, id = name });
}
}
else
{
return Json(new { statu = 202, msg = "请上传文件！" });
}
}

<tr>
<td>上传视频</td>
<td>
<div id="upl">上传视频</div>//马上这个会用js实例化
</td>
</tr>
<script>
 var uploader;
  $(function () {
    
    uploader = WebUploader.create({
      auto: true,
      swf: '/Scripts/Uploader.swf',
      server: '@Url.Action("Upload")',//控制器
      pick: '#upl',
        accept: {
          title: 'Images',
          extensions: 'mp4,flv,jpeg,bmp,doc,docx,rar,pdf',
        }
     
    })
  });
</script>