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.m4a is the file extension attached to names of files using the MPEG-4 Audio standard. The normal extension for any MPEG-4 file is .mp4, which is also mentioned in the MPEG-4 standard. The .m4a file extension has been popularized by Apple, which started using the .m4a file extension in their iTunes software and iPod music players to distinguish between MPEG-4 Video and Audio files. Currently, most software that supports MPEG-4 Audio also supports the .m4a extension. The most common type of .m4a files available are those using the AAC (Advanced Audio Coding) audio format, but other formats such as Apple Lossless and even mp3 files may be put inside a .m4a container file. You can normally safely rename the file extension of a .mp4 file containing only audio to .m4a or vice versa to get the file to properly play in your favorite audio player.

Protected MPEG-4 Audio

When these files have digital rights management (DRM) restrictions applied to them, their extension are changed to .m4p, the p standing for protected. Music files purchased from the iTunes Music Store have this extension.


When they contain audiobook data, MPEG-4 files have a .m4b extension.