I had a play with the Xara Video Container - loaded it to a Desktop 1280px, created a mobile variant 640px (and the placeholder was SHARED), set Export Scale-to-Fit-Width. All looks OK with the video centred through the transition from Desktop to Mobile.

https://initiostar.co.uk/demo/Vid-Container/ I too did not see an immediate need for the Class Name "hide"

A point maybe worth a mention, is where a designer wants an initial full page video to scroll with other content, "fixed" can be replaced "absolute" >> e.g. https://initiostar.co.uk/demo/Video/fullwidthscroll.htm

On the made with Xara website, the horizontal feature is I assume coded, something like this? https://webmadewell.com/background-i...-as-scrolling/ - would be great to have a Xara equivalent.