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MP4 file format

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MPEG-4 is a suite of standards which has many "parts", where each part standardizes various entities related to multimedia, such as audio, video, and file formats. To know more about various parts and what they mean, please see the entry for MPEG-4. MP4 redirects here. For other uses of the term MP4 see MP4_(disambiguation).
MP4 (MPEG-4 Part 14)
Filename extension
.mp4
Internet media type
video/mp4
Type codempg4
Developed byISO
Type of formatMedia container
Container forAudio, video, text
Extended fromQuicktime .mov
StandardISO/IEC 14496-14

MPEG-4 Part 14, formally ISO/IEC 14496-14:2003, is a multimedia container format standard specified as a part of MPEG-4. It is most commonly used to store digital audio and digital video streams, especially those defined by MPEG, but can also be used to store other data such as subtitles and still images. Like most modern container formats, MPEG-4 Part 14 allows streaming over the Internet. The official filename extension for MPEG-4 Part 14 files is .mp4, thus the container format is often referred to simply as MP4. Devices that play .mp4 files are referred to as MP4 players.

History of MP4

MPEG-4 Part 14 was based on Apple's Quicktime container format.[1] MPEG-4 Part 14 is essentially identical to the QuickTime MOV format, but formally specifies support for Initial Object Descriptors (IOD) and other MPEG features.[2]

.MP4 versus .M4A file extensions

The existence of two different file extensions for naming audio-only MP4 files has been a source of confusion among users and multimedia playback software. Since MPEG-4 Part 14 is a container format, MP4 files may contain any number of audio, video, and even subtitle streams, making it impossible to determine the type of streams in an MP4 file based on its filename extension alone. In response, Apple Inc. started using and popularizing the .m4a file extension. Software capable of audio/video playback should recognize files with either .m4a or .mp4 file extensions, as would be expected, as there are no file format differences between the two. Most software capable of creating MPEG-4 audio will allow the user to choose the filename extension of the created MPEG-4 files.

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

  • Audio-only MP4 files generally have a .m4a extension.
    • MP4 files with audio streams encrypted by FairPlay Digital Rights Management as sold through the iTunes Store use the .m4p extension.
    • Audio book and podcast files, which also contain metadata including chapter markers, images, and hyperlinks, can use the extension .m4a, but more commonly use the .m4b extension. An m4a audio file does not "bookmark" (remember the last listening spot) on an iPod, whereas m4b extension files do. Users can rename mp4 m4a file extensions m4b to activate this and faster listen iPod features.
  • MP4 files with audio and video generally use the .mp4 and .m4v extensions, occasionally .mp4v. To add to confusion sometimes raw MPEG-4 Visual bitstreams are named .m4v.
  • Mobile phones use 3GP, a simplified version of MPEG-4 Part 12 (a.k.a MPEG-4/JPEG2000 ISO Base Media file format, MPEG-4 Part 14 is a derivative of the standard from ISO Base file format too), with the .3gp and .3g2 extensions. These files also store non-MPEG-4 data (H.263, AMR, TX3G).

The common, but non-standard use of the extensions .m4a and .m4v is due to the popularity of Apple's iPod and the iTunes Store.

Data streams

Almost any kind of data can be embedded in MPEG-4 Part 14 files through private streams; the widely-supported codecs and additional data streams are:

Some private stream examples include Nero's use of DVD subtitles (Vobsub) in MP4 files.

M4P to MP3 Conversion Methods

There are two other methods to convert M4P to MP3 by bypassing the DRM control. The first method is to burn a copy to an audio CD and then rip it. Some software products take an even simpler and more automated method which allows user to burn music to a Virtual CD-RW disc and then automatically rip and encode the music stored on the Virtual CD-R. NoteBurner M4p converter is the typical example which uses this Virtual CD-RW drive method.

The second method is to use a recording software and sound card (utilizing the so-called "analog hole").

Notes

  • The .m4p is usually used as the music format for the iTunes Store DRM copy protected content, while .m4a is now being used by the iTunes Store for DRM-free, unprotected music files.

See also

Competing technologies

Compatible software

Compatible hardware

Notes

  1. ^ Apple Computer. "MPEG-4 Fact Sheet" (PDF).
  2. ^ http://lists.apple.com/archives/Streaming-server-developers/2001/Dec/msg00016.html
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