Zkoušel jsem si to:

 private void button1_Click(object sender, RoutedEventArgs e)
        {

            MessageBox.Show(RemoteFileExists(@"http://188.246.127.147:7999/c/primacool").ToString());
           
            mediaElement.MediaOpened += new RoutedEventHandler(mediaElement_MediaOpened);
            mediaElement.MediaFailed += new EventHandler<ExceptionRoutedEventArgs>(mediaElement1_MediaFailed);
            Uri myUri = new Uri(@"http://188.246.127.147:7999/c/primacool");
            mediaElement.UnloadedBehavior = MediaState.Manual;
            mediaElement.Source = myUri;
           
        }

        private void mediaElement_MediaOpened(object sender, RoutedEventArgs e)
        {
            
            mediaElement.Play();
        }

        void mediaElement1_MediaFailed(object sender, ExceptionRoutedEventArgs e)
        {
            MessageBox.Show(e.ErrorException.ToString());
        }

        private bool RemoteFileExists(string url)
        {
            try
            {
                //Creating the HttpWebRequest
                HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
                //Setting the Request method HEAD, you can also use GET too.
                request.Method = "HEAD";
                //Getting the Web Response.
                HttpWebResponse response = request.GetResponse() as HttpWebResponse;
                //Returns TURE if the Status code == 200
                return (response.StatusCode == HttpStatusCode.OK);
            }
            catch
            {
                //Any exception will returns false.
                return false;
            }
        }

Bohužel na řádku:
MessageBox.Show(RemoteFileExists(@"http://188.246.127.147:7999/c/primacool").ToString());
Vyhodí false.

Proč není "zdroj dostupný" nechápu.
Když ho hodím do VLC playeru, tak přehrává.

Když zjistíš proč to "nebere" ten zroj, měl bys mít vyhráno.

Zatím to háže file not found exception.