Get different Source Code

I have wrote a little downloader in c# for different sites with videos to download them.

On the site "youtubeunblock.com", I get a different source code from the page when I start a WebRequest in the program. On any browser -> View Source Code I get under the embed source another link for the file appears different from what I have on the Downloader.

The code for the request inside the downloader:

CookieContainer cookieJar = new CookieContainer();
HttpWebRequest myWebRequest = (HttpWebRequest)HttpWebRequest.Create(url);
myWebRequest.CookieContainer = cookieJar;
myWebRequest.Method = "GET";
HttpWebResponse myWebResponse =(HttpWebResponse)myWebRequest.GetResponse();
StreamReader myWebSource = new StreamReader(myWebResponse.GetResponseStream());
string myPageSource = string.Empty;
myPageSource= myWebSource.ReadToEnd();
myWebResponse.Close();
return myPageSource;

i can try to explain

When i browse to this Site and search a video - > look at the source code (over a browser) from this page i found a tag file=http://12345.flv?12345

when i took this link into a href=http://12345.flv?12345 i can download this file.

when i try to take the so开发者_运维问答urce code from this page over the Webrequest, then i get the follow link file=http://12345.flv?abcde <- this link won´t work

Can anyone explain me this?

Your question is very unclear, but I think that this site don't allow unregistered users to download from it, so your code won't work.