I need an iPhone file converter that works offline. Help me please.

Hello friends. I need an accessible iPhone app, an app that converts video to audio locally, meaning I want it to do the job entirely on the iOS device, without the need for an internet connection. Does this app exist? Everyone I meet converts online, which is not only inconvenient, but insecure.
If the application also converts text files, this will be an interesting differential. Help me please.
Thank you.