Hide background video on mobile and replace with mobile-only image

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Hi, I'd like to hide the background video at the top of my website for mobile and replace it with an image. For some reason, the video often glitches after a few loops on mobile and causes load speed issues. What code should I use to do this? The image that replaces the video should only be visible on mobile as well.

My site is auralumina.com and the theme is Prestige. Thanks!