plugin.php

<?php
class YouTubePlugin extends StudipPlugin implements SystemPlugin
{

    function __construct()
    {
        parent::__construct();

        StudipFormat::addStudipMarkup('youtube1', '\[youtube\]', '\[\/youtube\]', 'YouTubePlugin::markupYouTube');
        StudipFormat::addStudipMarkup('youtube2','\[(you)\](.*?)(?=\s|$)', null, 'YouTubePlugin::markupYouTube', 'links');
    }

    static function markupYouTube($markup, $matches, $contents)
    {
        $input = parse_url(isset($matches[2]) ? $matches[2] : $contents);
        if (isset($input['query'])) {
            parse_str(urldecode(html_entity_decode($input['query'])), $params);
        } else {
            $params['v'] = $input['path'];
        }
        $video = $params['v'];
        unset($params['v']);
        return sprintf('<iframe width="480" height="360" src="//www.youtube-nocookie.com/embed/%s?%s" frameborder="0" allowfullscreen></iframe>',
            htmlReady($video), htmlReady(http_build_query($params)));
    }
}