How to remux mka audiobook to m4b?

Question

I have some audiobooks in "mka" files (Matroska audio) that I wish to remux to the more-standard "m4b" container, which more players can read. Is there a way to do this without losing the chaptering and without reencoding (the codec is 8 kbps Opus).

Answer 1

Think I've figured it out.

set "FFMPEG=C:\Portable Apps\ffmpeg\ffmpeg.exe"
set "INPUT=%~n1.mka"
set "OUTPUT=%~n1.m4b"
"%FFMPEG%" -i "%INPUT%" -f opus -c copy "%OUTPUT%"