Interesting...

Seems there is some confusion: User Posted Link

"While the only official file extension defined by the standard is .mp4, various file extensions are commonly used to indicate intended content:

* MPEG-4 files with audio and video generally use the standard .mp4 extension.
* Audio-only MPEG-4 files generally have a .m4a extension. This is especially true of non-protected content."

Posted By: BerlinCanary, May 24, 16:42:18