Hi Radost,
Thanks for your post and welcome to the community
I would try this method to use a custom mp4: [Tutorial] Responsive Video using HTML Embed
I also recommend to create a web optimized .mp4 version of the original, I use handbrake for that.
Webflow allows you to use custom code in the html embed to create the iframe that will contain the video, see here: Custom code | Webflow University
I hope this helps, there are probably other solutions people have used and others may comment. The BG video is the only native option to upload a video to Webflow (at the moment).
I hope this helps.