Increasing size of video thumbnail on mouseover
Why not use the :hover pseudo class and have that trigger the size change? Probably easier than having to worry about event binding.
http://jsfiddle.net/nhzNM/

&lt;iframe class="videoPlayer" width="560" height="315" src="http://www.youtube.com/embed/90Omh7_I8vI?controls=0&amp;rel=0" frameborder="0" allowfullscreen&gt;&lt;/iframe&gt;
&lt;style type="text/css"&gt;
.videoPlayer {
    width: 560px;
    height: 315px;
    -webkit-transition: height,width 1s ease;
    -moz-transition: height,width 1s ease;
    -ms-transition: height,width 1s ease;
    -o-transition: height,width 1s ease;
    transition: height,width 1s ease;
}

.videoPlayer:hover {
    width: 650px;
    height: 365px;
}
&lt;/style&gt;


You could use the same setup for a thumbnail positioned in front of the video embed.