MP4 = MPEG-4
MP4 (*.mp4) is the global file extension for the official container format defined in the MPEG-4 standard ISO 14496-14.
MP4 Filename Extensions
- .mp4: the only official extension; used for both audio and video files (and advanced content)
- .m4a: introduced by Apple for aac/alac audio-only files.
NOTE: .m4a files can safely be renamed to .mp4 -- but the distinction between audio (m4a) and video (mp4) may be useful if you are going to share files, or if you tend to forget what files you have.
For complete details on MP4, see the following link: