Arcadier allows you to use videos on your main or hero panel using an MP4 link. A good place to find free stock video footage in MP4 formatting is https://coverr.co/
If you have an existing video that you would like to use, you could upload the video via Vimeo to obtain an MP4 link. Do note, however, that this is only possible with Vimeo Premium, Business and PRO. Alternatively, you could use another paid service which you are currently subscribed to.
To convert an existing video, you can download it (do make sure you have permission to do that) and then upload it on a video uploader.