Forrester

I specifically bought Debut in order to record an internmittent narration over a Powerpoint presentation which includes a video clip. The idea is to pause the video and make a brief comment. The official Youtube video guides appear to indicate that a Windows user can select more than one input channel for a recording, which I assume would meet my needs. I'm working on a Macbook running the latest update of Catalina and cannot see a way to set up two inputs for a recording. Am I missing something? TIA Clive