How to record audio over Powerpoint/OpenOffice slides?
You can actually record audio with a Screen Recording in Quicktime, you just need to set the proper option. Just open a new screen recording (⌃⌘N), then click the white triangle:



You'll get a popup menu with options to choose which sound input you want to record from:


Select the appropriate sound device, then start the recoding, and you'll be able to narrate as you record your screen.