M4A files are similar to .MP4 video files since both file types use the MPEG-4 container format. However, M4A files only contain audio data. The use of the “.m4a” extension arose due to the confusion 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.
In the aspect of quality, an M4A file with ALAC codec has the best original sound quality. Even M4A (AAC) delivers better quality than MP3 audio at the same bit rate