How to convert .aax files to .mp4 format.
Converting Audible Enhanced Audiobook Files directly to MPEG-4 Videos (.aax to .mp4 conversion) should be possible, but might not be necessary.
Simply try renaming the AAX file extension to MP4, since they are basically identical file types.
Alternatively, you can try some conversion solutions, such as the Audible Online Converter, which lets you convert AAX to MP3. You can then easily convert MP3 to MP4.
The database currently does not contain any aax software converter.