encode mp3 on iOS

I want to make sure I can do what I need to in Xojo before investing in “learning time”… Is it possible to make an iOS app that will record audio and encode it as .mp3? If so, what is the best way to do this?

Apple offers free mp4 via their frameworks.
But not mp3.

So what are my “non-free” options? Is it possible that mp3 is TOTALLY impossible on iOS?!

You could get a mp3 C library, build some dylib, include it with the app, call via declare, I think.

Or move the processing to a webservice to convert from MPEG 4 downto 3.