PHP在我的youtube脚本上出现致命错误

我在Youtube php脚本上收到以下错误：

Fatal error: Call to a member function getAttribute() on a non-object
in /home/web/public_html/youtube/home.php on line 8

代码为：

<?php
$vidID= $_GET['id'];
$url = "http://gdata.youtube.com/feeds/api/videos/". $vidID;
$doc = new DOMDocument;
$doc->load($url);
$title = $doc->getElementsByTagName("title")->item(0)->nodeValue;
$published = $doc->getElementsByTagName("published")->item(0)->nodeValue;
$duration = $doc->getElementsByTagName('duration')->item(0)->getAttribute('seconds');
//$durationformatted = ;str_pad(floor($duration/60), 2, '0', STR_PAD_LEFT) . ':' . str_pad($duration%60, 2, '0', STR_PAD_LEFT); not working atm :/
$name = $doc->getElementsByTagName("name")->item(0)->nodeValue;
$commentcount = $doc->getElementsByTagName('feedLink')->item(0)->getAttribute('countHint');
$averagerating = $doc->getElementsByTagName('rating')->item(0)->getAttribute('average');
$numberofraters = $doc->getElementsByTagName('rating')->item(0)->getAttribute('numRaters');
$statisticsviewcount = $doc->getElementsByTagName('statistics')->item(0)->getAttribute('viewCount');
echo "Title: ".$title."'nDuration: ".$duration." seconds'nPublished: ".$published."'nUsername/channel: ".$name."'nTotal Comments: ".$commentcount."'nCategory: ".$category."'nAverage rating: ".$averagerating." out of 5'nNumber of raters: ".$numberofraters."'nView count: ".$statisticsviewcount."'n";
?>

我该怎么解决这个问题？