The following screencast shows how a full page background video can be set up in Oxygen using Video Background plugin.
Summary: Add a Div, set the height to 100vh, set horizontal item alignment for children to Stretch, add Header and Footer, remove backgrounds so they are transparent, set margin-top: auto; for the footer so it gets pushed down to the bottom. Back in WordPress editor, specify the ID of div as the element to which video should be “applied” as background and upload/select video’s mp4, webm and jpg files.