Convert FLAC to M4A with FFMpeg Revision as of Monday, 14 September 2020 at 17:18 UTC

This is for macOS. You’ll need FFMpeg with this encoder.

brew tap homebrew-ffmpeg/ffmpeg

# or 'upgrade'. The "--HEAD" will fetch the latest release.
# Might save you trouble with ImageMagick versions.
brew install homebrew-ffmpeg/ffmpeg/ffmpeg --with-fdk-aac --HEAD

# Convert!
find . -name '*.flac' -exec sh -c 'ffmpeg -i "$1" -c:a libfdk_aac -b:a 320k "${1%.flac}.m4a"' _ {} \;

Problems

ImageMagick Version

Just install the latest ImageMagick and FFmpeg with --HEAD.

Could not find tag for codec h264 in stream #0 codec

FFmpeg is trying to transcode any cover art. To fix, just add a -c:v copy to the command.