Oembed is brilliant! If you’ve got an URL, a simple call to a page and you can get back a lovely bit of JSON telling you how to embed the content. If you haven’t read up on it here is the standards page http://oembed.com/
WordPress by default requests the standard swf embed from youtube. If you want to update your template to use the iFrame html5 player, YouTube have an iframe=1 parameter you can add when sending the oembed request. You can override the existing oembed provider inside your wordpress template using the following.
'http://www.youtube.com/oembed?iframe=1', true );
I’ve added it to my functions.php in my template, you could edit the class-oembed.php file directly if you wanted but any future updates will overwrite it.
Now all your clips will come through in html5 for all to see!