Ok I did some research, here is a diagram of my idea:
I will use a grabber with a loop, this will avoid having to buy a splitter (I only need one HDMI source).
To control the LEDs, an ESP32 with wled (usb or wifi, I don't know if wifi can create latency).
I need to find which LED to choose, and which grabber (I would like "HDMI IN 4K60fps" to "HDMI OUT 4K60FPS" so as not to lose image fluidity for 60fps content), do you have a reference to recommend to me? I found this:
DIGITNOW Capture Enregistrement dAcquisition Adaptateur
https://www.amazon.fr/dp/B097SZJ4LK?tag=hyperioforum-21
Capture Direct Streaming Enregistrement décalage
Thanks you