jsFiddle

• Run again
• Edit this fiddle

• Result
• HTML
• CSS

<div class="video">
    <div class="sleeve">
        <object type="application/x-shockwave-flash" data="http://www.youtube.com/v/UXjUQnSi9zE&amp;hl=en_US&amp;fs=1&amp;" width="480" height="385">
            <param name="movie" value="http://www.youtube.com/v/UXjUQnSi9zE&amp;hl=en_US&amp;fs=1&amp;" />
            <param name="allowScriptAcess" value="always" />
            <param name="allowFullScreen" value="true" />
        </object>
    </div>
</div>

.video    {
    height: 0;
    padding-bottom: 56.25%;
    padding-top: 25px;
    position: relative;
}
    .video .sleeve, .video OBJECT    {
        height: 100%;
        left: 0;
        position: absolute;
        top: 0;
        width: 100%;
    }