How to Convert M4B to MP3 With iTunes
Apple iTunes software and iPod devices utilize the .M4B file format extension for spoken-word audio tracks. If you want to use an .M4B audio on another type of audio player, you can use iTunes to can convert .M4B files to .MP3 format provided the file is not copyright-protected by digital rights management software (DRMS). This restriction applies to many .M4B files purchased from the iTunes store. If the file is protected, a message will be displayed when you try to convert it stating that the file is protected.
Open iTunes and import the .M4B file into iTunes if it is not already there.
Click the "Edit" menu and select "Preferences." The Preferences window opens.
Click the "General" button if it is not already selected. Click the "Importing Settings" button to the left of "When You Insert a CD."
Click the "Import Using" menu and select "MP3 Encoder." Click "OK."
Click "OK" to close the Preferences window.
Locate the .M4B file you want to convert. Most .M4B files are located in the "Books" section of iTunes.
Click the "Advanced" menu and select "Create MP3 Version." The .M4B file will be copied as a .MP3. You can keep both versions or delete the .M4B as desired.