Do not record narration in PowerPoint in Mac and expect to make it a video.

​PowerPoint Product Team [MSFT] (Admin, Office.com) responded  ·  Jan 24, 2018 Thanks for your feedback! The PowerPoint for Mac team is reviewing your suggestion to include audio narrations when exporting to video and will consider it in future planning rounds."

Much to my frustration, I discovered that if you record narration on PowerPoint on a Mac, the audio is stripped when it is converted to a video.  

When I was trying to troubleshoot, I found an (unhelpful) comment on powerpoint.uservoice.com saying it will be considered for future uses. 

Since I have Camtasia, the solution was just to record the screen with Camtasia and use a PC in the future ... but oh, how frustrating!

So you can make a video in PPT but it doesn't record the narration.