How they are able to interact with virtual world without having to wear or hold any VR device in Mixed Reality? [on hold]

I watched this video about an Interactive Mixed Reality game show and I would like to try out mixed reality in Unreal. I noticed they don't use any VR headset or using any handheld device to interact inside the virtual world.

I was wondering if they are using mocap or already setting up all the equipment inside the studio that receive inputs like a normal input device or there is another tricks that I've been missing out.

I've seen many mixed reality games that need VR device and stuff and the ones in that video is very interesting for me that I would like to try out in the future.

Any ideas on how they are able to interact with virtual world without having to wear or hold any VR device?

Sorry for the long post.