If you want to use video as a home page Cover area background, you’ll navigate to Theme Options -> Styling & Colors -> Cover background media, and choose Video as your preferred option. Once you do that, the Cover background video and Video placeholder image sections will appear on the panel, and you will be able to upload your video and video placeholder image.
A solid number of mobile devices are not supporting video backgrounds. Therefore, uploading a video placeholder image that will serve as a background image on that type of device, is highly recommended.