fetch url's in php video scripts???

Can anyone shed some light on how working fetch url's for video scripts are obtained? I've been trying to figure it out myself and find some consistancy in the process but it just seems pretty random to me.

Below is the exampl code file for a page that pulls videos from youtube and embeds them in a video script...It uses a fetch url (highlighted in red)...I don't know how that url was obtained ...And even in some case where I can...there doesn't seem to be any logical way to find the fetch url for other video sites...Can anyone explain this to me to make it easier to find these url's for different video sites and add them to a script..? Thank you...


Code:
<?php
function yt($ytsearch) {

	global $ytcurrenttag;
	global $ytvids;
	global $ytid;
	$ytvids = array();
	$ytid=0;
	
	function ytinsidethetag($ytparser, $ytdata){
		global $ytcurrenttag;
		global $ytvids;
		global $ytid;
		if(!strcmp(strtolower($ytcurrenttag),"title")) {
			$ytvids[$ytid]['type'] = "yt";
			$ytvids[$ytid]['title']=$ytdata;
			$ytvids[$ytid]['title'][0] = ucwords($ytvids[$ytid]['title'][0]);
		}
			
	}
	
	function ytopentag($ytparser, $ytdata, $ytattr=''){
		global $ytcurrenttag;
		$ytcurrenttag = $ytdata;
		global $ytvids;
		global $ytid;
		if(!strcmp(strtolower($ytcurrenttag),"media:player")) {
			$ytvids[$ytid]['link']=str_replace("watch?v=","v/",$ytattr['URL']);
			$ytvids[$ytid]['thumb']=str_replace("http://www.youtube.com/v/","http://img.youtube.com/vi/",$ytvids[$ytid]['link']);
			$ytvids[$ytid]['thumb'].="/2.jpg";
		}
	}
	
	function ytclosetag($ytparser, $ytdata){
		global $ytid;
		if(!strcmp(strtolower($ytdata),"entry"))
			$ytid++;
	}
	
	$ytxml_parser = xml_parser_create();
	
	xml_set_element_handler($ytxml_parser, "ytopentag", "ytclosetag");
	
	xml_set_character_data_handler($ytxml_parser, "ytinsidethetag");
	
	include_once("fetch.php");
	$ytdata = fetchrss("http://gdata.youtube.com/feeds/videos?vq=$ytsearch&start-index=1&max-results=50");
	if(!(xml_parse($ytxml_parser, $ytdata)))
		die("Error on line " . xml_get_current_line_number($ytxml_parser));
	
	xml_parser_free($ytxml_parser);
	
	return $ytvids;
}
?>