It’s hard to tell what you’re working with from the image, but I’ll assume newline breaks.
<?php
$string = "http://www.podcast.com/track.mp3
2207703
audio/mpeg";
echo "<pre>";
echo $string; // should show multiple rows
To grab the first line, try preg_match:
// now grab the first line
if( preg_match ('/^(.*)$/m', $string, $matches) ){
echo $matches[0]; // first line is the URL
}