M4A is Apple’s modification of MPEG-4 (MP4) media container containing audio files. Since the original media container could contain various data — video, audio, and others — Apple created its own extensions that would allow users to distinguish exactly what content is inside the file. Accordingly, the letter A at the end of the .m4a extension stands for Audio.
Such a container may contain files in AAC or ALAC formats - file formats with both lossy and lossless.
Technically, the extension can be easily renamed to .mp4 and then it can be used as a simple MP4 file. However, if you need to use such a file as regular audio, the easiest way is to extract its contents and convert it to MP3.
File type: Audio
File extension: .m4a, .mp4, .m4p, .m4b, .m4r, .m4v
Developed by: Apple
Initial release: 2001