Depends what you mean by easiest. You can also use ffmpeg to create a "screencast" with sound and it's just a couple of extra command-line options. E.G. the op

Depends what you mean by easiest. You can also use ffmpeg to create a "screencast" with sound and it's just a couple of extra command-line options. E.G. the options -f pulse -ac 2 -i default work well for me. Of course, if you don't know this or your machine's setup well, and you happen to have another device lying around, you're prone to pick it up and make the video that way instead. Which may be harder because then you have to get the video off the other device somehow. Lol, epistemology is an interesting field.