MPEG-4 Part 14
MPEG-4 Part 14 (MP4)
Relations between ISO Base Media File Format and MP4 File Format.svg
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]
Type code mpg4
Developed by International Organization for Standardization (ISO)
Type of format Media container
Container for Audio, video and text
Extended from QuickTime File Format and MPEG-4 Part 12
Standard(s) ISO/IEC 14496-14

MPEG-4 Part 14 or MP4 (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 video and digital audio 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. A separate hint track is used to include streaming information in the file. The only official filename extension for MPEG-4 Part 14 files is .mp4.

Some devices advertised as "MP4 Players" are simply MP3 Players that also play AMV video or some other video format, and do not necessarily play the MPEG-4 part 14 format.[2][3]

Contents

History of MP4

MPEG-4 Part 14 is an instance of more general ISO/IEC 14496-12:2004 (MPEG-4 Part 12: ISO base media file format) which is directly based upon QuickTime File Format.[4][5][6][7][8] 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.[9] 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.[10]

The MPEG-4 file format specification was created on the basis of the QuickTime format specification published in 2001.[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 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, Motion JPEG 2000).[4][17][18]

MP4 file format versions
Version Release date Standard Description
MP4 file format version 1 2001 ISO/IEC 14496-1:2001 MPEG-4 Part 1 (Systems), First edition
MP4 file format version 2 2003 ISO/IEC 14496-14:2003 MPEG-4 Part 14 (MP4 file format), Second edition

The MP4 file format defined some extensions over 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 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 www.mp4ra.org. The registration authority for code-points (identifier values) in "MP4 Family" files is Apple Computer Inc. and it is named in Annex D (informative) in MPEG-4 Part 12.[17] Codec designers should register the codes they invent, but the 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 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]

.MP4 versus .M4A filename extensions

M4A stands for MPEG 4 Audio and is a filename extension used to represent audio files.

The existence of two different filename extensions for naming audio-only MP4 files has been a source of confusion among users and multimedia playback software. Some file managers, such as Windows Explorer, look up the media type and associated applications of a file based on its filename extension. But 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 filename extension, which is used for MP4 containers with audio data in the Advanced Audio Coding (AAC) or its own Apple Lossless (ALE, ALAC) formats. Software capable of audio/video playback should recognize files with either .m4a or .mp4 filename 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 filename extension defined 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 .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 were sold through the iTunes Store use the .m4p extension. iTunes Plus tracks, that the iTunes Store currently sells, are unencrypted and use .m4a accordingly.
    • 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.
    • The Apple 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 but this extension is also sometimes used for video in MP4 container format.[21]
  • Mobile phones use 3GP, an implementation of MPEG-4 Part 12 (a.k.a MPEG-4/JPEG2000 ISO Base Media file format), similar to MP4. It uses .3gp and .3g2 extensions. These files also store non-MPEG-4 data (H.263, AMR, TX3G).

Data streams

Almost any kind of data can be embedded in MPEG-4 Part 14 files through private streams. 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-supported codecs and additional data streams are:[citation needed]

Other compression formats are less used: MPEG-2 and MPEG-1
Also MPEG-4 Part 3 audio objects, such as Audio 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) and Structured Audio Orchestra Language (SAOL)
Other compression formats are less used: Apple Lossless
Nero Digital uses DVD Video subtitles in MP4 files

Metadata

MP4 files can contain metadata as defined by the format standard, and in addition, can contain Extensible Metadata Platform (XMP) metadata.[citation needed]

See also

References

  1. ^ a b 3GPP2 (18 May 2007) (PDF). 3GPP2 C.S0050-B Version 1.0, 3GPP2 File Formats for Multimedia Services. 3GPP2. p. 67, 68. http://www.3gpp2.org/Public_html/specs/C.S0050-B_v1.0_070521.pdf. Retrieved 2009-06-12. 
  2. ^ "MP3≠MP4!区别和认识MP3与MP4的不同!". Beareyes. http://bj.beareyes.com.cn/2/lib/200510/26/20051026011.htm. 
  3. ^ "走出MP4误区:跟视频沾一边的播放器就是MP4". 西北IT网. http://www.cps365.com/news/200608/06/0712_0000021657.shtml. 
  4. ^ a b mp4ra.org - MP4 Registration authority. "References, MPEG-4 Registration authority". http://www.mp4ra.org/specs.html. Retrieved 2009-06-14. 
  5. ^ ISO (2006-04). ISO Base Media File Format white paper - Proposal. archive.org. Archived from the original on 2008-07-14. http://web.archive.org/web/20080714101745/http://www.chiariglione.org/mpeg/technologies/mp04-ff/index.htm. Retrieved 2009-12-26. 
  6. ^ ISO (2005-10). MPEG-4 File Formats white paper - Proposal. archive.org. Archived from the original on 2008-01-15. http://web.archive.org/web/20080115035235/http://www.chiariglione.org/mpeg/technologies/mp04-ff/index.htm. Retrieved 2009-12-26. 
  7. ^ ISO (2009-10). ISO Base Media File Format white paper - Proposal. chiariglione.org. http://mpeg.chiariglione.org/technologies/mpeg-4/mp04-ff/index.htm. Retrieved 2009-12-26. 
  8. ^ Apple Computer. "MPEG-4 Fact Sheet". http://images.apple.com/quicktime/pdf/MPEG4_v3.pdf. 
  9. ^ RE: QT vs MPEG-4
  10. ^ International Organization for Standardization (2003). "MPEG-4 Part 14: MP4 file format; ISO/IEC 14496-14:2003". http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=38538. Retrieved 2009-06-11. 
  11. ^ Apple Inc. (2001). "Classic Version of the QuickTime File Format Specification". http://developer.apple.com/standards/classicquicktime.html. Retrieved 2009-06-14. 
  12. ^ Library of Congress (2001). "MPEG-4 File Format, Version 1". http://www.digitalpreservation.gov/formats/fdd/fdd000037.shtml. Retrieved 2009-06-14. 
  13. ^ Network Working Group (2006). "MIME Type Registration for MPEG-4". http://tools.ietf.org/html/rfc4337#page-4. Retrieved 2009-06-14. 
  14. ^ International Organization for Standardization (2001). "MPEG-4 Part 1: Systems; ISO/IEC 14496-1:2001". http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=34903. Retrieved 2009-06-11. 
  15. ^ Library of Congress (2003). "MPEG-4 File Format, Version 2". http://www.digitalpreservation.gov/formats/fdd/fdd000155.shtml. Retrieved 2009-06-14. 
  16. ^ "MPEG-4 Systems General Issues". chiariglione.org. 2001-07. http://mpeg.chiariglione.org/faq/mp4-sys/sys-faq-sys4gen.htm. Retrieved 2010-04-11. 
  17. ^ a b c ISO (2008) (PDF). ISO/IEC 14496-12:2008, Information technology -- Coding of audio-visual objects -- Part 12: ISO base media file format. International Organization for Standardization. p. 88, 94. http://standards.iso.org/ittf/PubliclyAvailableStandards/c051533_ISO_IEC_14496-12_2008.zip. Retrieved 2009-05-30. 
  18. ^ International Organization for Standardization (2004). "MPEG-4 Part 12: ISO base media file format; ISO/IEC 14496-12:2004". http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=38539. Retrieved 2009-06-11. 
  19. ^ Steven Greenberg (2009). "Registration of ftyp's". http://www.ftyps.com/mp4reg.html. Retrieved 2009-06-15. 
  20. ^ Steven Greenberg (2009). "Complete List of all known MP4 / QuickTime 'ftyp' designations". http://www.ftyps.com/. Retrieved 2009-06-15. 
  21. ^ Doom9's Forum, MP4 FAQ, Retrieved on 2009-07-15
  22. ^ mp4ra.org - MP4 Registration authority, Registered Types - Codecs - ISO Code Points, Retrieved on 2009-07-14.

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