Video background not responsive on mobile

Hi, I’m new to wordpress and struggling with this!

My video background is playing on all device types but it doesn’t fill the space. On the ipad and mobile sizes it has big gaps above and below it. I read an earlier post here, saying video bgs don’t work on mobile, but it was a few years old. Is that still the case? If so, why is my video playing? I tried using a placeholder image but it displayed the image and the video at the same time.

http://54.252.250.31/wp-admin/customize.php?url=http%3A%2F%2F54.252.250.31%2F%3Fpreview_id%3D21517%26preview_nonce%3D0c5b166673%26_thumbnail_id%3D-1%26preview%3Dtrue

Thanks, Zoe