MP4 file format
MP4 (MPEG-4 Part 14) | |
---|---|
Filename extension |
.mp4 |
Internet media type |
video/mp4 |
Type code | mpg4 |
Developed by | ISO |
Type of format | Media container |
Container for | Audio, video, text |
Extended from | Quicktime .mov |
Standard | ISO/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.
- 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.
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.
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
- Container format (digital) definition and article
- Comparison of (audio/video) container formats
- List of multimedia (audio/video) codecs
Competing technologies
- DivX Media Format 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
- MPEG transport stream
- NUT patent-free open source and extensible multimedia container
- Ogg
- OGM ("Ogg Media", standard video container for Xiph.org codecs)
- ratDVD closed source proprietary format based on VOB (the DVD-Video container format)
- VOB the container format used in DVD-Video (uses .VOB .IFO and .BUP combined as extensions)
Compatible software
- 3ivx
- Amarok
- Banshee Music Player
- foobar2000
- GOM Player
- iTunes
- J. River Media Center
- jetAudio
- KSP Sound Player
- Media Player Classic
- MPlayer
- Nero Burning ROM (Nero ShowTime)
- QuickTime Player
- RealPlayer
- Songbird (software)
- The KMPlayer
- VLC media player
- Winamp
- Xbox Media Center
- Xine
- Zune
Compatible hardware
- Apple iPod
- KiSS 1600 (Hardware H.264/VC-1/MPEG-2 + Software MPEG-4 ASP DVD player)
- PlayStation 3
- PSP (Playstation Portable)
- Xbox 360
Notes
- ^ Apple Computer. "MPEG-4 Fact Sheet" (PDF).
- ^ http://lists.apple.com/archives/Streaming-server-developers/2001/Dec/msg00016.html