google.php

public static function videoIdFromGoogleUrl($source)
{
    $pattern = "/^(?:http:\/\/video.google.com\/(?:videoplay|googleplayer.swf)\?docid=([\w\-]+))/is";
    $matches = array();
    preg_match($pattern, $source, $matches);
    if (isset($matches[1])) return $matches[1];
    return $source;
}

youtube.php

public static function videoIdFromYoutubeUrl($source)
{
    $pattern = "/^(?:http:\/\/(?:www.)?youtube.com\/(?:watch\?v\=|v\/)([\w\-]+))/is";
    $matches = array();
    preg_match($pattern, $source, $matches);
    if (isset($matches[1])) return $matches[1];
    return $source;
}