There is moderate support in iTunes for some third-party .mp3 players, but they will not be able to play .mp4 AAC files (including content purchased from the iTunes Store). Apple offers a full-line of iPod products and accessories which will give you the best digital experience. Otherwise, you may enjoy our content on a computer or a CD, or you may convert the AAC files.
To re-encode the AAC (.mp4) files in the .mp3 format, first, download the content first into your iTunes application. Second, in the iTunes preferences, click on the "Advanced" icon and navigate to the "Importing" tab. Next, select "MP3 Encoder" in the "Import Using" menu. Finally, highlight the file(s) that you wish to convert, go to the "Advanced" menu, and click on "Convert Selection to .mp3".