aax2mp3 - convert aax audio book files (Audible) to mp3
                  or other audio formats supported by ffmpeg

        aax2mp3 [options] [-a authcode] -i inputfile

        aax2mp3 is Copyright (C) 2017,2019 by Josef Kleber
        License: GPLv3

        aax2mp3 provides a user-friendly  interface to  ffmpeg to  convert audio
        books in aax format into other audio formats - especially mp3! It serves
        the backup of personally purchased audio books, not to convert any audio
        books! aax2mp3 doesn't crack the DRM of audio books! It just uses ffmpeg
        and your personal Audible authcode  to convert your audio books to other
        audio formats. See AUTHCODE, how to obtain your personal authcode.

    Generic Program Information
        -h, --help
            Output a usage message and exit.
        -V, --version
            Output the version number and exit.
        -v, --verbose
            Create more vorbose output.

    Audio Book Selection
        -i AUDIOBOOK, --input AUDIOBOOK, --audiobook AUDIOBOOK
            Select an audio book (aax format).
        -a AUTHCODE, --authcode AUTHCODE
            Set the authcode for ffmpeg conversion.

    Mode Selection
        -S, --single
            Output one big single audio file.
        -C, --chapter (default)
            Output the  audio book  divided into chapters.  This  probably  only
            works  for  the  mp3  format!  See  option  --postprocessing  for  a
        -p, --postprocessing
            Create intermediate mp3 files  and post process them to the desired
            audio format.
        -k, --keepsingle
            Keep the one big audio file in chapter mode.

    Output File Format
        -b BITRATE, --bitrate BITRATE
            Set the bitrate of output file (default: bitrate of input file).
        -c CODEC, --codec CODEC
            Set the codec of the output file. (default: libmp3lame)
            See: ffmpeg -encoders | grep -e '^ A'
            -> acc, flac, libopus, libvorbis, ...
        -e EXTENSION, --extension EXTENSION
            Set the file extension of the output file. (default: mp3)
            -> acc, flac, opus, ogg, ...

    Metadata (default: metadata of input file)
        -G GENRE, --genre GENRE
            Set genre metadata of output file.
        -T TITLE, --title TITLE
            Set title metadata of output file.
        -A ARTIST, --artist ARTIST
            Set artist metadata of output file.
        -B ALBUM, --album ALBUM
            Set album metadata of output file.
        -R ALBUM_ARTIST, --albumartist ALBUMARTIST
            Set album_artist metadata of output file.
        -M COMMENT, --comment COMMENT
            Set comment metadata of output file.
        -D DATE, --date DATE
            Set date metadata of output file.
        -Y COPYRIGHT, --copyright COPYRIGHT
            Set copyright metadata of output file.
            Set cover image (JPG).

        Instead of using the -a option to set the authcode,  you can also set it
        using the AAX2MP3_AUTHCODE environment variable, e.g. by adding:
            export AAX2MP3_AUTHCODE="12345678"
        to your ~/.bash_profile

        Any  player or  converter dealing  with aax files  do need  a so  called
        authcode. This is a personalized code embedded as DRM. There are several
        ways to obtain your personal Audible authcode. Google is your friend!
        You may be interested in:

    aax2mp3 -i B077NH5P9Q_ep7.aax -a 12345678 --single
        converts B077NH5P9Q_ep7.aax into one single mp3 file.

    aax2mp3 --audiobook B077NH5P9Q_ep7.aax -v -a 12345678 --title 'Titanic 03'
    --artist 'Titanic' --codec libvorbis --extension ogg --bitrate 160
        converts B077NH5P9Q_ep7.aax into chapter divided ogg vorbis files with a
        bitrate of 160 bk/s and a few metadata changes.