Paraphrased from the former www.m4a.com site: MP4 can be used for MPEG 4 video files, combined video and audio files, or just plain MPEG 4 audio. M4A files contain only MPEG 4 Audio. Apple started using M4A to identify files unprotected by digital rights management; note that protected QTA_AAC files carry the M4P and and M4B (for bookmarkable files) extensions. Apple felt that MP4 was too general (video, video/audio, or audio) and might confuse some media players. Until recently, encoder and player software like Nero and Compaact used .mp4 for audio files while WinAmp 5.02, Apple iTunes, and others used .m4a. Today, most audio software developers allow you to choose the file extension you prefer.
I need to add some .mp4 videos to a course in my LMS (Moodle) on a Windows 2008 R2 server. I'm using IIS 7.5 as the web server. While searching the www for the correct way to do it I've found several references that say you should use "Mime Type = video/mp4" for the .mp4 extension. Other references say you should use "Mime Type = video/mpeg".
MPEG-4 Part 14 or MP4 is a digital multimedia container format most commonly used to store video and audio, but it can also be used to store other data such as subtitles and still images. Like most modern container formats, it allows streaming over the Internet. The only filename extension for MPEG-4 Part 14 files as defined by the specification is .mp4. MPEG-4 Part 14 (formally ISO/IEC 14496-14:2003) is a standard specified as a part of MPEG-4.
The International Organization for Standardization approved the QuickTime file format as the basis of the MPEG-4 file format. The MPEG-4 file format specification was created on the basis of the QuickTime format specification published in 2001. The MP4 (.mp4) file format was published in 2001 as the revision of the MPEG-4 Part 1: Systems specification published in 1999 (ISO/IEC 14496-1:2001). In 2003, the first version of MP4 format was revised and replaced by MPEG-4 Part 14: MP4 file format (ISO/IEC 14496-14:2003). The MP4 file format was generalized into the ISO Base Media File Format ISO/IEC 14496-12:2004, which defines a general structure for time-based media files. It in turn is used as the basis for other multimedia file formats (for example 3GP, Motion JPEG 2000). A list of all registered extensions for ISO Base Media File Format is published on the official registration authority website www.mp4ra.org. This registration authority for code-points in "MP4 Family" files is Apple Inc. and it is named in Annex D (informative) in MPEG-4 Part 12. 041b061a72