protect php result

Question

hii i had simple php file to protect wmv files from downloading and stolen the file is like this

<?php

// get-file.php


$id = (isset($_GET["id"])) ? strval($_GET["id"]) : "1";

// lookup
$url[1] = 'http://mlfat.ledawy.net/Files/eng/moslslat/mosque/1.wmv';
$url[2] = 'URL';
$url[3] = 'URL';



header('Content-Type: text/plain');
echo("$url[$id]");
?>

and i embedd the movies like this http:// mlfat.ledawy.net/Files/eng/moslslat/mosque/mosque.php?id=1 but if you call this link you can find the source url can i have some protection ?? tried a lot of adding a php session variable so that the script can not be accessed directly. thank you