AAX files are Audible Enhanced Audiobook files developed by Audible, which are commonly used by audiobook services. It’s the improved version of the AA file format, including more features such as images and links. However, AAX files are DRM-protected. So, you can only play them on specific players like Audible.M4A represents MPEG 4 Audio. It is the successor to MP3 and it can store various types of audio content such as audiobooks, songs, and podcasts. M4A file extensions are used to save both lossy and lossless compression formats. You can access M4A files on most media players.