$re = '/<iframe[^>]*src=[\"|\']([^\'\"]+)[\"|\'][^>]*>/i';
$str = '<iframe src="http://flashx.tv/embed-76oom84mwi54-640x360.html" frameborder="0" marginwidth="0" marginheight="0" scrolling="no" width="640" height="360"></iframe>
<a href="http://fullpeliculas.com/mcfarland-usa/">
<div class="im">
<img src="http://fullpeliculas.com/wp-content/uploads/2014/11/McFarland-USA-150x150.jpg">
</div>
<p>
McFarland: Sin lĂmites</p></a>';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php