Hello,
I'm used to work with ffmpeg, and I have a personal server to test everything.
I'm able to help you reduce a moov file size, both fastly & with a high quality.
I'm already done similar projects, you can check for reviews on my profile.
Looking forward to hearing from you,
Antoine Camusat
PS: Je peux travailler en français si cela est plus simple pour vous. (I'm able to work in french if that is easier for you)