As Fugiman said, the actual video will always maintain an aspect ratio of 16:9. If you want to outer box to have the same dimensions as the video, you will need to use JS and calculate the needed height of the outer box based on the width of the video.
For example (using jQuery syntax):
var videoWidth = $(’[video element selector]’).width();
$(’[outer box selector]’).heigth(videoWidth * (9/16));
This may not be completely correct, but it should help you get started.