<div id="video-wrapper">
<video width="640" height="360" style="width: 100%; height: 100%;" id="player1">
<source/>
</video>
</div>
demos/mediaelementplayer-responsive.html 2.9.3 ( github). , , ... ! - ( jquery):
var newHeight = 360 / 640 * newWidth;
$('#video-wrapper').css('width',newWidth);
$('#video-wrapper').css('height',newHeight+'px');