I would like to take the picture of the mobile phone display live (not about the APP function).  I have an HDMI switch with which I currently record the video signal via HDMI from 2 GoPros via the capturr card on the notebook and stream it live.  Now I wanted to take the picture of the Flyapp mobile phone display as the third source.  I have a corresponding adapter that outputs the display as HDMI - only this does not work with the APP and the remote control!  This does not recognize a cell phone ... Has anyone already done something like this successfully?  Maybe via Miracast?  Or is there an adapter that works with the remote control and the APP?

With a type of Miracast yes, but not using splitter, i have tried a couple of splitters to no avail, Ken Heron on Youtube managed it with a Micracast device BUT, they also need a power source, he used a portable battery pack, look it up on YT

Thank you!

Theres an app called Prism that can do that -

This enables a * direct * live stream, but not an additional video source via HDMI. But that is exactly what I am looking for. I did another successful test via Miracast - I will now buy a Miracast dongle from Amazon for my project.

The constellation is then as follows:
2x GoPro via MediaMod via HDMI and
1x Miracast dongle via HDMI on an HDMI switch.
Then via HDMI to a capture card (HDMI to USB) - on the notebook, as a "webcam". So I can now choose between THREE video sources and continue to use them as a live stream like a webcam on the notebook (e.g. stream on YT - even without at least 1000 Folower for a stream via mobile phone ...).
The only problem remains the reception via LTE when I'm mobile.