Hey Reuben,
For my app, I’ve used promo.com to create few intro videos. Took me few hours and $39 but it was fun. You can see one here: https://www.youtube.com/watch?v=KbulmIm5ru0. It is not art and definitively I can do better, however overall I think that it is a good solution so someone that has no experience in video editing.
Scroll down to the “App submission” on this article and you should find a few more info and videos I’ve made: https://www.shopify.com/partners/blog/front-end-app
Hope it helps