Convert all flac files in folder to m4a using ffmpeg and libfdk_aac

convert_flac_to_aac.sh

# on os x use  brew to get ffmpeg with libfdk_aac
brew install ffmpeg --with-fdk-aac

# convert and use m4a as file extension
find . -name '*.flac' -exec sh -c 'ffmpeg -i "$1" -c:a libfdk_aac -b:a 320k "${1%.flac}.m4a"' _ {} \;

Currently, you must do the following to install ffmpeg with libfdk_aac:

brew tap homebrew-ffmpeg/ffmpeg
brew install homebrew-ffmpeg/ffmpeg/ffmpeg --with-fdk-aac

For me, ffmpeg also reported Could not find tag for codec h264 in stream #0, codec not currently supported in container until I added -map a:0 to specify that there shouldn't be a video track. So the final version looked like this:

find . -name '*.flac' -exec sh -c 'ffmpeg -i "$1" -map a:0 -c:a libfdk_aac -b:a 320k "${1%.flac}.m4a"' _ {} \;

Thanks to both of you for the help!