An M4A file is an audio file saved in the MPEG-4 format and encoded with either the Advanced Audio Coding (AAC) codec or the Apple Lossless Audio Codec (ALAC). It may store various types of audio content, such as songs, podcasts, and audiobooks.

MPEG-4 is a multimedia container format used to store both compressed audio and video data. The format is used by .MP4 files, which store audio and video data. M4A files only contain audio data, which led to the .m4a extension that stands for “MPEG-4 Audio.” This name change helped distinguish between MPEG-4 video files and MPEG-4 audio-only files.

The iTunes Store provides songs in the M4A format. These songs are encoded using AAC compression, which significantly reduces the size of each file. Songs that include copyright protection have an .M4P extension.

NOTE: Windows Media Player 11 requires the K-Lite Codec Pack in order to play M4A files. Windows Media Player 12 (included with Windows 7) provides native support for the M4A format.