audiblez[1] does exactly that and handles the ffmpeg fu part for you, and will output a m4b file which audio book players will support. 1. https://github.com/s

audiblez[1] does exactly that and handles the ffmpeg fu part for you, and will output a m4b file which audio book players will support. 1. https://github.com/santinic/audiblez https://github.com/santinic/audiblez