Full Browser Width Video Background HTML/CSS

[Initiostar]

I am trying to source/identify the correct HTML/ CSS to display an autoplay loop banner video such that it extends to the full width of the browser.

Right now, it sits perfectly on the page (1200px wide) and I can crop the height of the video no problem to my chosen pixels to achieve a banner. The effect I am trying to achieve is similar to: https://www.thewatermansbarnes.co.uk, but in this case resizing the browser maintains the height of the video, rather than retaining its correct aspect.

My test site is http://www.design.initiostar.co.uk which works great, without the usual Xara video controls. My XAR file is attached.

Any help much appreciated; I looked at the various W3C options and could play around with these, but I am assuming someone has already solved this issue.

Thanks,

Gary