Compositing unreal content onto live video


I have a couple of question I’m hoping someone smarter than myself can help me out with. I’m relatively new to unreal, coming over from C4D…

I have a project in which I need to create some CG content in Unreal which I will be compositing onto a live camera video feed. The issue I’m running into seems simple, but for the lift of me I can’t figure it out.

I’m using the HDRI Backdrop to create my reflections and base lighting which is working great. What I can’t figure out, is how I can use the HDRI backplate *just *for the reflections and lighting and hide them from the “camera” view so that I can composite the 3d asset w/ reflections and lighting onto my live video.

The second issue I’m having, is how would I accomplish capturing the shadows on the ground plane in a way that can be composited onto the video w/o rendering the actual ground plane. For instance, in C4D you would create a “Shadow Catcher” material that will render out a shadow pass that you can use for compositing. I’ve seen examples of people doing this in Unreal, but, again, can’t figure it out.

The screenshot below is a very basic chrome ball example. The objective is for the final output from Unreal to capture the chrome ball with it’s reflections and ground shadow w/o any visible environment so that I could composite it onto the live video… I guess you could think of it as a faked augmented reality effect.

Hope that makes sense - Really appreciate any advice here!
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