Background video showing up pixelated

So I’m uploading a video I purchased from shutter shock on my site as a background video. I’ve uploaded the video when it was only 1.1mb and then when it was 4.8 mb and both keep showing up super pixelated, here is an image of how it looks: . why is this happening and how can I fix it?

Here is my site Read-Only: LINK
(how to share your site Read-Only link)

I’m having this same issue