Y no sera mas facil asi?
Código PHP:
Ver original<?php
$dom = new DOMDocument();
$dom->load('tuRutaAlXML.xml');
$tagMedia = $dom->getElementsByTagName('media:player')->item(0)->getAttribute('url');
$thumb = $dom->getElementsByTagName('media:thumbnail')->item(0)->getAttribute('url');
$thumbWidth = $dom->getElementsByTagName('media:thumbnail')->item(0)->getAttribute('width');
$thumbHeight = $dom->getElementsByTagName('media:thumbnail')->item(0)->getAttribute('height');
?>