Evitar descarga de videos en Wordpress

<?php
class Cipher {
    private $securekey, $iv;
    function __construct($textkey) {
        $this->securekey = hash('sha256',$textkey,TRUE);
        $this->iv = mcrypt_create_iv(32);
    }
    function encrypt($input) {
        return base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $this->securekey, $input, MCRYPT_MODE_ECB, $this->iv));
    }
    function decrypt($input) {
        return trim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $this->securekey, base64_decode($input), MCRYPT_MODE_ECB, $this->iv));
    }
}

if($_GET['on']=="1"){
	$cipher = new Cipher('miclavesegura');
	$encryptedtext = $cipher->encrypt(urldecode($_GET['in']));

	echo '<input type="text" value="'.urlencode($encryptedtext).'" size="200"><br/>';
}else if($_GET['v']!=""){
	if(stristr($_SERVER['HTTP_REFERER'],"misitio.com")===FALSE){
		header("location: http://www.w3schools.com/html/mov_bbb.mp4");
		die();
	}
	$cipher = new Cipher('miclavesegura');
	$decryptedtext = $cipher->decrypt($_GET['v']);

	if($decryptedtext!="")
		header('location: '.$decryptedtext);
	else
		header("location: http://www.w3schools.com/html/mov_bbb.mp4");
}
die();
?>

<p><video controls><source src="http://misitio.com/ONvideo.php?v=trvVLUeNieCGkX1lZkSzLd05pVmMESoRVE4Iu7uzsrCdM1xauxXilr5XaFY9pcOMEIQa782GERdjmpqTz7R6Hg%3D%3D" type="video/mp4">Your browser does not support HTML5 video.</video></p>