In one sentence, describe what the following article is about:

Apple has created several MP4-variants, including M4A, M4P, M4B, and M4R. These files can all be played in iTunes, but you can use iTunes to convert them to MP3 format as well. You cannot use iTunes to convert an MP4 video file into an MP3 audio file. Use Avidemux to convert your video files to MP3 audio. You can download and install iTunes for free from apple.com/itunes/download/. Click the "File" or "iTunes" menu and select "Add to Library". Browse for the files you want to add. Click the "General" tab if it isn't opened automatically. Import Settings... button. In the "Import Using" menu, select "MP3 Encoder". Select "Create MP3 Version" from the menu that appears. The new MP3 version will be created and placed in the same location as the original file. You can right-click the file and select "Show in Windows Explorer" or "Show in Finder" to open the folder containing the file.

Summary:
Know the different types of MP4 audio files. Download and install iTunes. Add the files that you want to convert to the iTunes library. Click the "Edit" or "iTunes" menu and select "Preferences". Click the . Right-click on the file you want to convert in iTunes.