I've written code to parse metadata out of an M4A. I'm sure Apple does a good job of it given they've done that in iTunes for 20+ years, but it's a lot less do

I've written code to parse metadata out of an M4A. I'm sure Apple does a good job of it given they've done that in iTunes for 20+ years, but it's a lot less documented and straightforward than ID3v2, as imperfect and hacky as that format is. As a result, I can pretty trivially edit ID3 from a shell script, but dealing with M4A metadata still feels like a black box. (After typing that, I realize that calling it a "black box" is a pretty good pun on MP4 box formats..)