$('.open-fancybox').fancybox({
    'afterShow': function() {
        $('#mediaelement').mediaelementplayer();
    }
});

<a class="open-fancybox" href="#fancybox">
<div id="#fancybox">
    <video id="#mediaelement" src="...mp4">
</div>

<script>
    $(document).ready(function(){
      $('video').mediaelementplayer( {
      flashName: '/path_to_mediaelement_swf/flashmediaelement.swf',
      });
   });
  </script>

<video width="320" height="240" poster="poster.jpg" controls="controls" preload="none">
    <!-- MP4 for Safari, IE9, iPhone, iPad, Android, and Windows Phone 7 -->
    <source type="video/mp4" src="myvideo.mp4" />
    <!-- WebM/VP8 for Firefox4, Opera, and Chrome -->
    <source type="video/webm" src="myvideo.webm" />
    <!-- Ogg/Vorbis for older Firefox and Opera versions -->
    <source type="video/ogg" src="myvideo.ogv" />
    <!-- Optional: Add subtitles for each language -->
    <track kind="subtitles" src="subtitles.srt" srclang="en" />
    <!-- Optional: Add chapters -->
    <track kind="chapters" src="chapters.srt" srclang="en" />
    <!-- Allow the plugin to generate the object markup, preventing the swf source from loading too early  -->

</video>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js" type="text/javascript"></script>
<script src="fancybox/jquery.fancybox-1.3.4.pack.js" type="text/javascript"></script>
<script src="mediaelement/mediaelement-and-player.min.js" type="text/javascript"></script>
<link href="mediaelement/mediaelementplayer.css" type="text/css" rel="stylesheet">
<link href="fancybox/jquery.fancybox-1.3.4.css" type="text/css" rel="stylesheet">

$(document).ready(function() {
  $('a.inline').fancybox({
    'transitionIn'  : 'fade',
    'transitionOut' : 'fade'
  });
  $('video').mediaelementplayer({
    pluginPath: 'mediaelement/'
  });
});

<div>
    <a class="inline" href="#video"><img src="images/homepage/video.png"></a>
</div>
<div style="display:none;">
    <div id="video">
      <video width="640" height="360" poster="images/homepage/videoPreview.jpg">
        <source type="video/mp4" src="video/uA_V1.mov">
      </video>
    </div>
</div>