<script type="text/javascript" src="../fancybox2/source/jquery.fancybox.js?v=2.1.0"></script>
<link rel="stylesheet" type="text/css" href="../fancybox2/source/jquery.fancybox.css?v=2.1.0" media="screen" />
<script type="text/javascript">
    $(document).ready(function() {
    $('.fancybox-media').fancybox({
    openEffect  : 'none',
    closeEffect : 'none',
    helpers : {
    media : {}
    }
   });
  });
</script>

<a href="youtube url" class="fancybox-media iframe"><img /></a>

$('.fancybox-media').fancybox({
    type : 'iframe',
    // existing stuff
});