Custom UI integrating Facetime Video?

I want to make a custom UI that integrates each video feed from my FaceTime group activity participants.

I found the app Share+ in the App Store integrates the video from each FaceTime participant into it's own UI, so I know it's possible.

Can anyone point me to the relevant documentation that shows me how I can get to the video of each FaceTime group member to put in my own AVSampleBufferDisplayLayer or otherwise?

Custom UI integrating Facetime Video?
 
 
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