Artwork not showing in preview when setting up claim page

Hi there, I’m trying to set up a claim page to mint an open edition (its a 10 second .mp4) but the artwork, when uploaded, doesn’t show in the claim page and I’m instead just shown a grey video box - can anyone assist?

screenshot attached

What is the file format of the video? How big is it? Did you end up publishing the page? Some more info maybe helpful here.