I bought an audio book from audible and want to convert it to mp3 from aa because my phone doesn't support the format. Is there any way to do that?
From their manual:
Audible AAX files are encrypted M4B files, and they can be decrypted by specifying a 4 byte activation secret.
ffmpeg -activation_bytes 1CEB00DA -i input.aax -vn -c:a copy output.mp3
Since the file is encrypted, you will need the activation secret in order to decrypt and convert.