I'd forgotten that my Mac Mini had a fan. All it took was feeding a batch of seven videos into Handbrake for transcoding...
(And thanks to those who suggested Handbrake; just takes a few clicks, without having to understand what's going on).
Aaaand... The fan stopped as soon as the batch finished. Not like closing a rogue tab in Chrome, then.
Figured out how to template the output file name, and save the size as a preset. Not it's just add files, click Start Queue.
Welcome to thundertoot! A Mastodon Instance for 'straya