Hi there!
I recently noticed a bug when the audiobook containers are written. No matter how you get audio data into ABB as soon as you write an audiobook (m4a or m4b, aac or aac-he) the book somehow is written as video container.
It plays fine in itunes and on iOS devices, but you can't use macOS' quicklook preview. I noticed the issue with the generated files when I tried to upload the files to the tonies.de cloud. They couldn't process the files.
As soon as you do the following with the files
Code:
ffmpeg -i generated.m4b -acodec copy -vcodec copy fixed.m4b
the files work just fine.
There must be an issue with container as the streams are fine (thus the copy option of ffmpeg works fine)
Rico
PS: I can't share sample files publicly (copyright!) but I'm fine with sending a sample file to the developers if needed