<?php

$string = "magnet:?xt=urn:btih:0eb69459a28b08400c5f05bad3e63235b9853021&dn=Splinter.Cell.Blacklist-RELOADED&tr=udp%3A%2F%2Ftracker.com%3A80&tr=udp%3A%2F%2Ftracker.publicbt.com%3A80&tr=udp%3A%2F%2Ftracker.istole.it%3A6969&tr=udp%3A%2F%2Ftracker.ccc.de%3A80&tr=udp%3A%2F%2Fopen.demonii.com%3A1337";

$regex = "/^.*?btih\:([^&]+).*?tr\=([^&]+).*$/";

if ( preg_match($regex, $string, $resultados) ) {
    echo $resultados[1] . "\n";
    echo $resultados[2] . "\n";
}

?>