MPEG-4 Part 14

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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.

1 History of MP4
- 1.1 .MP4 versus .M4A file extensions
2 Data streams
3 NOTES
4 See also
- 4.1 Competing technologies
- 4.2 Compatible software
5 Notes
6 External links

[edit] 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 IODs and other MPEG features [1].

[edit] .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 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.
3G 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.

[edit] 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:

Video: MPEG-4 Part 10 (also known as H.264 and MPEG-4 AVC), MPEG-4 Part 2, MPEG-2, and MPEG-1.
Audio: AAC (also known as MPEG-2 Part 7), MP3 (also known as MPEG-1 Audio Layer 3), MPEG-4 Part 3, MP2 (also known as MPEG-1 Audio Layer 2), MPEG-1 Audio Layer 1, CELP (speech), TwinVQ (very low bitrates), SAOL (MIDI).
Subtitles: MPEG-4 Timed Text (also known as 3GPP Timed Text).

Some private stream examples include Nero's use of DVD subtitles (Vobsub) in MP4 files. They are however not a part of the MPEG-4 file format standard and programs are not required to support them.

[edit] NOTES

The .m4p is usually used as the music format for the iTunes Store.

[edit] See also

[edit] Competing technologies

MPEG transport stream
Ogg
VOB the container format used in DVD-Video (uses .VOB .IFO and .BUP combined as extensions), this is what ratDVD is based on and thus support everything ratDVD does
ratDVD closed source proprietary format based on VOB (the DVD-Video container format)
DivX Media Format (DMF) from DivX, Inc. (uses .divx as extension), includes support for DVD-Video like menus
Matroska (MKV) open source (uses .mkv as extension) includes support for DVD-Video like menus
OGM ("Ogg Media", standard video container for Xiph.org codecs), supports everything that ratDVD does except for menus
MP4 (MPEG-4 Part 14) container format standard specified as a part of MPEG-4, currently support everything NUT does
NUT patent-free open source and extensible multimedia container, currently supports everything ratDVD does except for menus