So how did I create the videos? I do have access to two phones, both of which are capable of recording videos, so the obvious answer was to use one phone to record another. However, keeping both phones steady while recording and playing was harder than I thought; the phone that is recording doesn't need to be held by a person, but it does need to be positioned between the player ("hello") and the phone I'm playing on. Asking a fellow human to hold the recording-phone tends to feel a bit ridiculous as they have to reach around you and keep the phone super-steady, which isn't that easy.
The solution hit me like a birthday present when, for my birthday, I got a present that turned out to be a phone holder for my car. Perfect! Its suction cup held it securely to a table while I played the games around it. The only challenge now is to make a vaguely entertaining video that's short but also shows off the best features of the games. And also where my thumb isn't always in the way.
Here's the Worldcrafter one:-
Since the game involves tilting the phone, that provided an extra challenge for keeping the phone in-view.