Hi @sui.x,
I understand you're looking to play video fills on your Figma Sites file.
Just for your reference, Figma Sites doesn't currently support native video uploads. So, if you try to upload a video as a fill, it won't play back in the Preview view.
Instead, to add a video, we recommend using the embed features in Sites. You can use the YouTube embed, or the generic URL or HTML embed if your video is hosted on a different platform. You can find more information on how to use these features here: Insert blocks, embeds, webpages, and design libraries into a site.
Also, if you'd like to see this feature implemented, we'd love for you to post your requests in our Suggest a Feature category. Our Product Managers regularly review community suggestions there, so you can directly share your ideas with them.
Thanks,