How do I record the iPad camera for use with ARKit?

I want to have the ability to record only the camera feed from the iPad for my ARKit app. How do I achieve this?
Can I record straight from the camera?
Can I somehow record the application but use some culling mask to hide everything for the recorder only (I don't want to have to hide the virtual objects for the user while recording)?

I want to then be able to replay this video in the app, replacing (or just overlaying on top of) the normal webcam feed.