Many thanks to John Harrison for showing me how easy iMovie is to use.
YouTube must by default pick the middle frame of the whole video for the thumbnail screen? I’ve updated it to use a different frame, but they say it can take six hours to take effect. Meanwhile, here’s a great video apparently about hysteresis!
YouTube has synced my change for which frame gets used for the video still, so the joke about the hysteresis video doesn’t work any more.