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MP4 file format

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For other parts of the MPEG-4 standard, see MPEG-4.
"MP4" redirects here. For other uses, 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.

Some devices advertised as "MP4 players" are simply AMV video capable MP3 players, and do not play MPEG-4 part 14 or any other MPEG-4 format.

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, MPEG-4 files may contain any number of audio, video, and even subtitle streams, making it impossible to determine the type of streams in an MPEG-4 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:

  • 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.
    • MPEG-4 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 cannot "bookmark" (remember the last listening spot), whereas .m4b extension files can. Users can rename .mp4 or .m4a file extensions to .m4b to activate these features.
    • The Apple Inc. iPhone uses MPEG-4 audio for its ringtones but uses the .m4r extension rather than the .m4a extension.
  • 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), 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, the iTunes Store, and the Xbox 360 (in which support for mp4 formatted files was added in the fall 2007 Dashboard update).

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.

Notes

See also

Competing technologies

Compatible software

Compatible hardware

Notes

  1. ^ Apple Computer. "MPEG-4 Fact Sheet" (PDF).
  2. ^ RE: QT vs MPEG-4
  3. ^ "MP4 Player". Playing MP4 Video Files In Windows.
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