Video from database set to fill container (banner background video)

Hello—it’s a year later, and I’m still having this same issue. I’m needing to use the single video player in order to have a looping background video without a play button visible—but then the black bars on the side show up, and I cannot figure out how to make them go away.

How is it possible to be having this trouble, when the stretch is so simple in the normal Wix editor? And is the GIF suggestion still the only workaround? GIF files are extremely large, so the opposite of ideal for websites.

Please help—I need to get material to a client today, and made the transition from normal Wix to Editor X this week thinking that these elements would be equally simple to integrate, but this is significantly pushing me back when I’m on a tight deadline. Thanks!