hi,
I'm not sure if this will work or not. But I would like give you another approach and you can review it. If you would like to try, I can help to discuss with you, if it is success, you can award me later. If it is not what you expected, you can have a reference, that is good for you.
I suggest this approach as the following model:
Internet -> Wordpress -> video link (which is hosting by a iptables/nginx) -> S3 bucket.
So, instead of indicating a direct link to client in your wordpress, try to post it via nginx link, like:
http://your_nginx/buckage/video1.mp4...
So, in this nginx server, you can try to limit the number of concurrent session from a IP via nginx plugin or using iptables to do the concurrent limitation.
So that means from an IP, it can't open more than 2 sessions to download a video vian nginx. That may help to adapt your requirement.
Regards,
--T