@naturepunk Yeah. I also went down that rabbithole briefly when I found this great instructions by @madskjeldgaard
ffmpeg for Artists: A Cookbook for Audio and Video Processing on the Command Line ... with Examples!
A guide to using ffmpeg for artists. ffmpeg is a free tool that allows you to create, convert and manipulate video, really quickly and without opening a heavy GUI-based program. You can script it to make full use of it's power and convert folders of files for example. The following is a cookbook of handy examples I myself use to easily create videos for social media, websites, etcetera – mostly from a source material of audio files and/or photos. I hope you find it useful.
hyaline.systems (hyaline.systems)
And I also looked into the problem of extracting channels from a multichannel file and found sox and especially libsndfile https://libsndfile.github.io/libsndfile/
In contrast to ffmpeg their main focus is audio.