Also thought I'd add the stack I used:

App is native SwiftUI. Backend is entirely Firebase, Firestore, Auth, Functions, Storage.

I'm currently looking into setting up Gemini as a backup service in case openAI is down. In addition, looking at expanding the app to a more general "caption" app - supporting starting with text drafts, AI rewrites, hashtag groupings and more, also possibly getting into closed captioning videos and other similar things.