I checked your link, and even did a "command + f" search. I saw no mentions of the words "audio," "sound," "input", nor "output."

Without some sort of fancy hardware or hacky software, I am not sure if it's possible -- at least not as of 6 or so months ago when I was looking for it.

To test:

Use the link above and try to record the audio of something like a YouTube video while recording the screen playing the video. If you can manage to get this to work, please share your results. I would be so obliged. This is not my goal of the software, but it's a quick test to show you what I am looking for.