Add wmode=transparent as param.
Html solution
<iframe title="YouTube video player"
width="480" height="390"
src="http://www.youtube.com/embed/lzQgAR_J1PI?wmode=transparent"
frameborder="0"
>
jQuery solution:
$(document).ready(function () {
$('iframe').each(function(){
var url = $(this).attr("src");
$(this).attr("src",url+"?wmode=transparent");
});
});
Source http://www.scorchsoft.com/news/youtube-z-index-embed-iframe-fix