Problems with the inbox and YouTube player

I would like to display a shadow under my tabs on YouTube, and I am having problems when I have different videos. I can make it work when I wrap a static div, but this does not work well with videos of different sizes. If that helps, they seem to always have the same width (640 pixels), and the height depends on the camera / video.

Is there a better way to do this, maybe it's possible to apply it to an iframe? I am noob with CSS and I can not find the answer on the web.

Any ideas?

My code:
Html:

<div id="videoclip">
<iframe width="640" height="510" src="http://www.youtube.com/embed/l4hMvo71p4M?rel=0&wmode=transparent&showinfo=0&start=11" frameborder="0" allowfullscreen></iframe>
</div>

CSS

 #videoclip{
width: 640px;
height: 510px;
box-shadow: 5px 5px #818181;
-webkit-box-shadow: 5px 5px 5px #818181;
-moz-box-shadow: 5px 5px 5px #818181;
}