The proper way to embed a video and open it in a lightbox would look like this (there’s no point in using iframe I think):
<a href="http://youtube.com/watch?v=XSGBVzeBUbk" rel="lightbox-1">My YouTube Video</a>
<a href="http://vimeo.com/35699279" rel="lightbox-2">My Vimeo Video</a>
Of course, you can use image instead of My Video text.
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