I have these https://www.amazon.com/gp/product/B07H9TYSB9/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

coming out of my NVR, and I use it to send HDMI over to my TV's from the garage where the NVR is, over my house ethernet. It uses multicast to send the data. Maybe there's a way to capture it?