docker image that take all mp3 files from the current folder, concats them and converts the result to m4b using ffmpeg.
docker pull martyca/mp3_2_m4b:latest
In the directory with the mp3 files run:
docker run -t -v "$(pwd):/tmp/workdir" martyca/mp3_2_m4b:latest
If this is something that you intent to do often, consider adding the following alias:
alias mp3_2_m4b='docker run -t -v "$(pwd):/tmp/workdir" martyca/mp3_2_m4b:latest'
https://hub.docker.com/repository/docker/martyca/mp3_2_m4b
https://github.com/martyca/mp3_2_m4b
https://hub.docker.com/r/jrottenberg/ffmpeg/
ffmpeg:4.4-ubuntu