Wikipedia

MP4 file format

(Redirected from.m4a)
"MP4" redirects here. For other uses, seeMP4 (disambiguation).

MPEG-4 Part 14,orMP4,is adigitalmultimediacontainer formatmost commonly used to storevideoandaudio,but it can also be used to store other data such assubtitlesand still images. Like most moderncontainer formats,it allowsstreamingover theInternet.The onlyfilename extensionfor MPEG-4 Part 14 files as defined by the specification is.mp4.MPEG-4 Part 14 (formallyISO/IEC14496-14:2003) is a standard specified as a part ofMPEG-4.

MP-4 Part 14
MPEG-4 Part 14 extends over ISO Base Media File Format (MPEG-4 Part 12).[1]
Filename extension
.mp4,.m4a,.m4p,.m4b,.m4r and.m4v[Note 1]
Internet media type
video/mp4
audio/mp4
Type codempg4
Developed byInternational Organization for Standardization

International Electrotechnical Commission
Initial releaseOctober 2001;23 years ago(2001-10)
Latest release
ISO/IEC 14496-14:2020
January 2020;4 years ago(2020-01)
Type of formatContainer format
Container forAudio, video and text
Extended fromQuickTime File FormatandMPEG-4 Part 12
StandardISO/IEC 14496-14
Open format?No[2][3]
Free format?No[2]

Portable media playersare sometimes advertised as "MP4 players",although some are simplyMP3 playersthat also playAMV videoor some other video format and do not necessarily play the MPEG-4 Part 14 format.

History

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MPEG-4 Part 14 is an instance of the more generalISO/IEC14496-12:2004 (MPEG-4 Part 12:ISO base media file format), which is directly based upon theQuickTime File Format,which was published in 2001.[4][5][6][7][8][9]MPEG-4 Part 14 is essentially identical to the QuickTime File Format but formally specifies support for Initial Object Descriptors (IOD) and other MPEG features.[10]MPEG-4 Part 14 revises and completely replaces Clause 13 of ISO/IEC 14496-1 (MPEG-4 Part 1: Systems), in which the file format for MPEG-4 content was previously specified.[11]

The MPEG-4 file format, version 1, was published in 2001 as ISO/IEC 14496-1:2001, which is a revision of the MPEG-4 Part 1: Systems specification published in 1999 (ISO/IEC 14496-1:1999).[12][13][14]In 2003, the first version of the MP4 file format was revised and replaced by MPEG-4 Part 14: MP4 file format (ISO/IEC 14496-14:2003), commonly named as MPEG-4 file format version 2.[15][16]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 file formats in the family (for example, MP4,3GP,andMotion JPEG 2000).[5][17][18]

MP4 file format versions
Version Release date Standard Description Edition
1 2001 ISO/IEC 14496-1:2001 MPEG-4 Part 1: Systems First
2 2003 ISO/IEC 14496-14:2003 MPEG-4 Part 14: MP4 file format First
2 2018 ISO/IEC 14496-14:2018 MPEG-4 Part 14: MP4 file format Second
2 2020 ISO/IEC 14496-14:2020 MPEG-4 Part 14: MP4 file format Third

The MP4 file format defined some extensions over the ISO Base Media File Format to support MPEG-4 visual/audio codecs and various MPEG-4 Systems features such as object descriptors and scene descriptions. Some of these extensions are also used by other formats based on the ISO base media file format (e.g., 3GP).[1]A list of all registered extensions for ISO Base Media File Format is published on the official registration authority website. The registration authority for code-points (identifier values) in "MP4 Family" files is Apple Inc., and it is named in Annex D (informative) in MPEG-4 Part 12.[17]Codec designers should register the codes they invent, but registration is not mandatory,[19]and some invented and used code-points are not registered.[20]When someone is creating a new specification derived from the ISO Base Media File Format, all the existing specifications should be used both as examples and as a source of definitions and technology. If an existing specification already covers how a particular media type is stored in the file format (e.g., MPEG-4 audio or video in MP4), that definition should be used, and a new one should not be invented.[17]

Filename extensions

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While the onlyfilename extensiondefined by the standard is.mp4,various filename extensions are commonly used to indicate intended content:

  • MPEG-4 files with audio and video generally use the standard.mp4extension.
  • Audio-only MPEG-4 files generally have a.m4aextension. This is especially true of unprotected content.
    • MPEG-4 files with audio streams encrypted byFairPlaydigital rights managementas were sold through theiTunes Storeuse the.m4pextension.iTunes Plustracks, that the iTunes Store currently sells, are unencrypted and use.m4aaccordingly.
    • Audiobookandpodcastfiles, which also contain metadata including chapter markers, images, and hyperlinks, can use the extension.m4a,but more commonly use the.m4bextension.
    • The AppleiPhoneuses MPEG-4 audio for its ringtones but uses the.m4rextension rather than the.m4aextension.
  • RawMPEG-4 Visualbitstreams are named.m4vbut this extension is also sometimes used for video in MP4 container format.[21]
  • Mobile phonesused to use3GP,an implementation of MPEG-4 Part 12 (a.k.a. MPEG-4/JPEG2000 ISO Base Media file format), similar to MP4. It uses.3gpand.3g2extensions. These files also store non-MPEG-4 data (H.263,AMR,TX3G). In practice, most (if not all) low end phones and feature phones recorded in this format, as most (if not all) other mobile phones andsmartphonesrecord MP4 files using the.mp4 file extension, and some high end phones[which?]can record in.raw.By the time that4Gtechnology was widespread, 3GP started to be phased out, and is now rarely seen.

Data streams

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Most kinds of data can be embedded in MPEG-4 Part 14 files throughprivate streams.A separate hint track is used to include streaming information in the file. The registered codecs for MPEG-4 Part 12-based files are published on the website of MP4 Registration authority (mp4ra.org),[22]but most of them are not widely supported by MP4 players. The widely supportedcodecsand additional data streams are (but many more are also supported, including audio like FLAC orTrueHD):[23][24]

Other compression formats are less used:MPEG-2andMPEG-1
AlsoMPEG-4 Part 3audio objects, such asAudio Lossless Coding(ALS),Scalable Lossless Coding(SLS),MP3,MPEG-1 Audio Layer II(MP2),MPEG-1 Audio Layer I(MP1),CELP,HVXC(speech),TwinVQ,Text To Speech Interface (TTSI) andStructured Audio Orchestra Language(SAOL)
Other compression formats are less used:Apple Lossless,Free Lossless Audio Codec(added in late 2018), andOpus(added in late 2018)[26]
Nero DigitalusesDVD Videosubtitles in MP4 files

Themoov atomcontains information about video resolution, frame rates, orientation, display characteristics, and more. It might be placed at the beginning or end of the file. In the latter case, the video file is not playable if the file is incomplete (truncated).[27][28][29][30]

Metadata

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MP4 files can containmetadataas defined by the format standard, and in addition, can containExtensible Metadata Platform(XMP) metadata.

See also

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References

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  1. ^ab3GPP2 (18 May 2007)."3GPP2 C.S0050-B Version 1.0, 3GPP2 File Formats for Multimedia Services"(PDF).Third Generation Partnership Project 2.pp. 67, 68. Archived fromthe original(PDF)on 7 October 2009.Retrieved2009-06-12.{{cite web}}:CS1 maint: numeric names: authors list (link)
  2. ^abMPEG-4 File Format, Version 2(Full draft). Sustainability of Digital Formats. Washington, D.C.: Library of Congress. 25 April 2023.Retrieved23 February2024.
  3. ^Information technology – Coding of audio-visual objects – Part 14: MP4 file format(Standard) (3rd ed.).ISO.January 2020. ISO/IEC 14496-14:2020.
  4. ^Apple Inc. (2001)."Classic Version of the QuickTime File Format Specification".Archivedfrom the original on 2009-08-28.Retrieved2009-06-14.
  5. ^abmp4ra.org - MP4 Registration authority."References, MPEG-4 Registration authority".Archivedfrom the original on 2018-08-19.Retrieved2018-08-29.{{cite web}}:CS1 maint: numeric names: authors list (link)
  6. ^"ISO Base Media File Format white paper - Proposal".Leonardo Chiariglione.International Organization for Standardization.April 2006. Archived fromthe originalon 2008-07-14.Retrieved2009-12-26.
  7. ^"MPEG-4 File Formats white paper - Proposal".Leonardo Chiariglione.International Organization for Standardization.October 2005. Archived fromthe originalon 2008-01-15.Retrieved2009-12-26.
  8. ^"ISO Base Media File Format white paper - Proposal".Leonardo Chiariglione.International Organization for Standardization.October 2009.Archivedfrom the original on 2021-04-29.Retrieved2014-10-31.
  9. ^Apple Computer."MPEG-4 Fact Sheet"(PDF).Archived fromthe original(PDF)on 2014-10-31.
  10. ^"RE: QT vs MPEG-4".Archived fromthe originalon 2007-05-10.Retrieved2007-03-30.
  11. ^International Organization for Standardization (2003)."MPEG-4 Part 14: MP4 file format; ISO/IEC 14496-14:2003".Archivedfrom the original on 2016-10-10.Retrieved2009-06-11.
  12. ^Library of Congress (2001)."MPEG-4 File Format, Version 1".Archivedfrom the original on 2017-03-20.Retrieved2009-06-14.
  13. ^Y. Lim; D. Singer (2006)."MIME Type Registration for MPEG-4".RFC Editor.doi:10.17487/RFC4337.Archivedfrom the original on 2021-05-06.Retrieved2009-06-14.
  14. ^International Organization for Standardization (2001)."MPEG-4 Part 1: Systems; ISO/IEC 14496-1:2001".Archivedfrom the original on 2016-08-19.Retrieved2009-06-11.
  15. ^Library of Congress (2003)."MPEG-4 File Format, Version 2".Archivedfrom the original on 2009-06-25.Retrieved2009-06-14.
  16. ^"MPEG-4 Systems General Issues".chiariglione.org. July 2001.Archivedfrom the original on 2010-04-13.Retrieved2010-04-11.
  17. ^abc"ISO/IEC 14496-12:2008, Information technology -- Coding of audio-visual objects -- Part 12: ISO base media file format".International Organization for Standardization.2008. pp. 88, 94. Archived fromthe original(ZIP)on July 6, 2016.Retrieved2009-05-30.
  18. ^International Organization for Standardization (2004)."MPEG-4 Part 12: ISO base media file format; ISO/IEC 14496-12:2004".Archivedfrom the original on 2016-08-19.Retrieved2009-06-11.
  19. ^Greenberg, Steven (2009)."Registration of ftyp's".Archivedfrom the original on 2009-10-24.Retrieved2009-06-15.
  20. ^Greenberg, Steven (2009)."Complete List of all known MP4 / QuickTime 'ftyp' designations".Archivedfrom the original on 2018-01-21.Retrieved2009-06-15.
  21. ^Doom9's Forum, MP4 FAQArchived2006-01-11 at theWayback Machine,Retrieved on 2009-07-15
  22. ^mp4ra.org - MP4 Registration authority,Registered Types - Codecs - ISO Code PointsArchived2019-08-23 at theWayback Machine,Retrieved on 2009-07-14.
  23. ^Chapman, Nigel; Chapman, Jenny (2004).Digital multimedia(2. ed.). Chichester [u.a.]: Wiley.ISBN978-0-470-85890-5.
  24. ^"The 'MP4' Registration Authority".mp4ra.org.Archivedfrom the original on 2023-10-07.Retrieved2023-08-31.
  25. ^"AV1 Codec ISO Media File Format Binding".aomediacodec.github.io.Archivedfrom the original on 2024-04-05.Retrieved2024-04-27.
  26. ^"Encapsulation of Opus in ISO Base Media File Format".2018-08-28.Archivedfrom the original on 2019-01-06.Retrieved2019-01-05.
  27. ^JK (25 January 2013)."Das Moov Atom und wo es stehen sollte".JKdigital(in German).Archivedfrom the original on 11 August 2020.Retrieved11 August2020.
  28. ^"Fehlerhaft kopierte MP4-Datei reparieren"(in German). preamp.org. November 2013.Archivedfrom the original on 2020-08-11.Retrieved2020-08-11.
  29. ^eZs3 media service (1 March 2011)."Checking Metadata or Moov Atom Location".ezs3.Archivedfrom the original on 11 August 2020.Retrieved11 August2020.{{cite web}}:CS1 maint: numeric names: authors list (link)
  30. ^Levkov, Maxim."Understanding the MPEG-4 movie atom | Adobe Developer Connection".adobe.AdobeDeveloper Network. Archived fromthe originalon 2021-01-30.Retrieved11 August2020.
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