$youtube = preg_replace("#\[youtube\](.*?)\[/youtube\]#si","<object style=' width: 640px; height: 390px'><param name='movie' value='http://www.youtube.com/v/\\1' /><param name='allowFullScreen' value='true' /><param name='allowScriptAccess' value='always' /><embed src='http://www.youtube.com/v/\\1' type='application/x-shockwave-flash' allowfullscreen='true' allowScriptAccess='always' width='640' height='390'></object>",$string);