How to capture screen using a private API in iOS 10?

I was the developer for an app called iCapture now known as iProRec which was a non jailbroken screen recorder that made its way on the App Store. I know how to record using airplay mirroring and I want to see if it is possible to do the same but with no wifi. I know it will use private API but I'm just curious to know if it is possible still with iOS 10 frameworks. What would be the best place to start?