Anders M. Anderson method for responsive media-sharing embeds:
http://amobil.se/2011/11/responsive-embeds/


FIRST: remove any width/height attributes from the HTML of your embedded object.


This object might still have intrinsic width/height, so we'll apply styling to a box that will contain the embed:


figure.video-box {
    position: relative;
    padding-bottom: 56.25%; /* 16/9 ratio */
    padding-top: 30px; /* IE6 workaround*/
    height: 0;
    overflow: hidden;
}

figure.video-box iframe,
figure.video-box object,
figure.video-box embed {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}