To set a background video for your section, just go to the section toolbar, click the background icon, and then click the Video tab. Choose your video provider and then paste in the URL for the video like you see here:
You can also use the settings for “Aspect Ratio” to match the size and orientation of the video that you want to use.
“Show on Mobile” is not recommended as most mobile browsers will block the automatic playback of videos. The section background image will be used instead of the video if you toggle that setting to “No”