www.makemkv.com

Makemkv conversion fails if i specify conversion to AAC or try to use the AAC setting, otherwise it works fine on Mint 19 64bit.
I have FAAC installed.

Any suggestions?

From the build instructions:

Please note that most distributions ship a very outdated version of libavcodec (either from ffmpeg or libav projects). You will have to compile a recent ffmpeg (at least 2.0) if you need a FLAC encoder that handles 24-bit audio. Also you will have to enable libfdk-aac support in ffmpeg in order to use AAC encoder.

I imagine the first question would have to be, does that exact statement equate to the intent behind your assertion that "I have FAAC installed." ... Possibly extreme short-hand, but the two things don't seem quite equal to me.

If not, return to that point.
download ffmpeg tarball from http://ffmpeg.org/download.html- configure and build ffmpeg: or with libfdk-aac support followed by configure and build makemkv-oss: remove temporary ffmpeg files: ---------------------
I wasn't bothered about FLAC support, so I didn't do any of that. If I ran into your issue 7 days+ into the 60 day period, I'd definitely have forgotten I chose not to mess with updating libavcodec beyond my distros norm, and that that would affect FLAC capabilities.

I don't know that what you're doing does need 24-bit FLAC support, or that you didn't already do this, but it's probably worth being very clear on the matter, since the developer went to so much trouble to thoroughly document it. No?