Autoplay videos are disabled on mobiles.
It's not a theme issue but mobile devices specification.
Mobile developers intentionally disabled media autoplay on mobile devices in order to protect user’s bandwidth. Many data providers charge based on the amount of data consumed, so the mobile developers decided it was in the best interest of the user to not have a video automatically begin playing when the page loaded so it would not start racking up data charges.
To present a video for mobile users you have to add it in the page content.