public function extractYoutubeId($sUrl)
    {
        preg_match('/^https?\:\/\/www\.youtube\.com\/watch\?v=([a-zA-Z0-9_\-]+)$/', $sUrl, $aMatches);

        if (!empty($aMatches[1])) {

            return $aMatches[1];

        } else {

            preg_match('/^https?\:\/\/youtu\.be\/([a-zA-Z0-9_\-]+)$/', $sUrl, $aMatches);

            if (!empty($aMatches[1])) {

                return $aMatches[1];
            }
        }

        return null;
    }