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MPEG-4 is a standard used primarily to compress audio and video (AV) digital data. Introduced in late 1998, it is the designation for a group of audio and video coding standards and related technology agreed upon by the ISO/IEC Moving Picture Experts Group (MPEG). The uses for the MPEG-4 standard are web (streaming media) and CD distribution, conversation (videophone), and broadcast television, all of which benefit from compressing the AV stream.
MPEG-4 absorbs many of the features of MPEG-1 and MPEG-2 and other related standards, adding new features such as (extended) VRML support for 3D rendering, object-oriented composite files (including audio, video and VRML objects), support for externally-specified Digital Rights Management and various types of interactivity. AAC (Advanced Audio Codec) was standardized as an adjunct to MPEG-2 (as Part 7) before MPEG-4 was issued.
Most of the features included in MPEG-4 are left to individual developers to decide whether to implement them. This means that there are probably no complete implementations of the entire MPEG-4 set of standards. To deal with this, the standard includes the concept of "profiles" and "levels", allowing a specific set of capabilities to be defined in a manner appropriate for a subset of applications.
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MPEG-4 Parts
MPEG-4 consists of several standards—termed "parts"—including the following:
Part 1 (ISO/IEC 14496-1): Systems: Describes synchronization and multiplexing of video and audio. For example Transport stream.
Part 2 (ISO/IEC 14496-2): Visual: A compression codec for visual data (video, still textures, synthetic images, etc.). One of the many "profiles" in Part 2 is the Advanced Simple Profile (ASP).
Part 3 (ISO/IEC 14496-3): Audio: A set of compression codecs for perceptual coding of audio signals, including some variations of Advanced Audio Coding (AAC) as well as other audio/speech coding tools.
Part 4 (ISO/IEC 14496-4): Conformance: Describes procedures for testing conformance to other parts of the standard.
Part 5 (ISO/IEC 14496-5): Reference Software: Provides software for demonstrating and clarifying the other parts of the standard.
Part 7 (ISO/IEC 14496-7): Optimized Reference Software: Provides examples of how to make improved implementations (e.g., in relation to Part 5).
Part 8 (ISO/IEC 14496-8): Carriage on IP networks: Specifies a method to carry MPEG-4 content on IP networks.
Part 9 (ISO/IEC 14496-9): Reference Hardware: Provides hardware designs for demonstrating how to implement the other parts of the standard.
Part 10 (ISO/IEC 14496-10): Advanced Video Coding (AVC): A codec for video signals which is technically identical to the ITU-T H.264 standard.
Part 11 (ISO/IEC 14496-11): Scene description and Application engine, also called BIFS; can be used for rich, interactive content with multiple profiles, including 2D and 3D versions.
Part 12 (ISO/IEC 14496-12): ISO Base Media File Format: A file format for storing media content.
Part 13 (ISO/IEC 14496-13): Intellectual Property Management and Protection (IPMP) Extensions.
Part 14 (ISO/IEC 14496-14): MPEG-4 File Format: The designated container file format for MPEG-4 content, which is based on Part 12.
Part 15 (ISO/IEC 14496-15): AVC File Format: For storage of Part 10 video based on Part 12.
Part 16 (ISO/IEC 14496-16): Animation Framework eXtension (AFX).
Part 17 (ISO/IEC 14496-17): Timed Text subtitle format.
Part 18 (ISO/IEC 14496-18): Font Compression and Streaming (for OpenType fonts).
Part 19 (ISO/IEC 14496-19): Synthesized Texture Stream.
Part 20 (ISO/IEC 14496-20): Lightweight Scene Representation (LASeR).
Part 21 (ISO/IEC 14496-21): MPEG-J Graphical Framework eXtension (GFX) (not yet finished - at "FCD" stage in July 2005, FDIS January 2006).
Part 22 (ISO/IEC 14496-22): Open Font Format Specification (OFFS) based on OpenType (not yet finished - reached "CD" stage in July 2005)
Profiles are also defined within the individual "parts", so an implementation of a part is ordinarily not an implementation of an entire part.
MPEG-1, MPEG-2, MPEG-7 and MPEG-21 are other suites of MPEG standards.
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Licensing
MPEG-4 is patented proprietary technology. This means that, although the software to create and play back MPEG-4 videos may be readily available, hypothetically a license would be needed to use it legally. Patents covering MPEG-4 are claimed by over two dozen companies. There is no easy way to license MPEG-4 and a so-called MPEG Licensing Authority can license patents required for MPEG-4 visual techniques from a wide range of companies (audio is licensed separately). A one stop shop is currently not possible; these articles claim that AT&T is trying to sue companies such as Apple over alleged MPEG-4 patent infringement. This AT&T action against Apple illustrates that it is hard to know which companies actually have patents covering MPEG-4.
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Alternatives
Open source alternatives to encapsulate AV.
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Container format|Containers
See also OGM, which is a fork of Ogg.
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Video codec|Video Codecs
x264 - H.264 (MPEG-4 part 10) implementation.
FFmpeg codecs - codecs in the libavcodec library from the FFmpeg project (FFV1, Snow, MPEG-1, MPEG-2, MPEG-4 part 2, MSMPEG-4, H.264, WMV2, SVQ3, MJPEG, HuffYUV, Indeo and others).
Tarkin - an experimental lossy video codec under development by the Xiph.org Foundation based on 3-D wavelet compression
Theora - Based on VP3, part of the Ogg Project.
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Audio codec|Audio Codecs
FLAC - Lossless compression.
iLBC - Low bitrate voice compression.
Musepack - Lossy compression; an attempt to replicate the MP3 format.
Speex - Low bitrate compression, primarily voice.
TTA - Lossless compression
Vorbis - Lossy compression; developed by Xiph.org.
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See also
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Links from the main article
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