As I have been using PowerPoint a fair bit recently, I noticed a template for Microsoft Office Mix. It lead me to install a free PowerPoint add-in that enables me to add optional audio and video to the presentation before uploading to the Mix website ( see https://mix.office.com/ ).
At first, I didn’t realise that my voice was being recorded, so I did it again … but maybe I should keep my mouth shut!
You can see my initial efforts at : https://mix.office.com/watch/1xf8jyin4s364