If you have existing files in other formats (like CD rips) and want them in .m4a :
Open the iTunes app and go to the Store or Library tab. itunes-m4a-download-blog
Ensure your download format is set to "High Quality" (256kb/s AAC) . If you have Lossless enabled, some files may download in a different container (like .movpkg ), so switching back to "High Quality" ensures you get a standard .m4a file. 2. Downloading Purchased Music If you have existing files in other formats