How to Record Webcam while video plays?

Hello there!

I recorded a screen of me going through steps in a system.

Now, I want to record my webcam (video & audio) to explain my steps throughout the recording.

However - I cannot find an option to play the video while I record the webcam. I can only either record the screen and webcam *or* record just the screen (and the video/screencast disappears). 

Ideally - I play the recorded screencast, and then I record my webcam of me talking about each step as it happens.

Thank you for any help you can provide!