MPEG-4 is a collection of methods defining compression of audio and visual (AV) digital data. It was introduced in late 1998 and designated a standard for a group of audio and video coding formats and related technology agreed upon by the ISO/IEC Moving Picture Experts Group (MPEG) under the formal standard ISO/IEC 14496. Uses of MPEG-4 include compression of AV data for web (streaming media) and CD distribution, voice (telephone, videophone) and broadcast television applications.
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.
MPEG-4 is still a developing standard and is divided into a number of parts. Companies promoting MPEG-4 compatibility do not always clearly state which "part" level compatibility they are referring to. The key parts to be aware of are MPEG-4 part 2 (MPEG-4 SP/ASP, used by codecs such as DivX, Xvid, Nero Digital and 3ivx and by Quicktime 6) and MPEG-4 part 10 (MPEG-4 AVC/H.264, used by the x264 codec, by Nero Digital AVC, by Quicktime 7, and by next-gen DVD formats like HD DVD and Blu-ray Disc).
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.
Initially, MPEG-4 was aimed primarily at low bit-rate video communications; however, its scope was later expanded to be much more of a multimedia coding standard. MPEG-4 is efficient across a variety of bit-rates ranging from a few kilobits per second to tens of megabits per second. MPEG-4 provides the following functionalities:
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MPEG-4 provides a series of technologies for developers, for various service-providers and for end users.
The MPEG-4 format can perform various functions, among which might be the following:
MPEG-4 consists of several standards—termed "parts"—including the following:
| Part | Number | Title | Description |
|---|---|---|---|
| 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 6 | ISO/IEC 14496-6 | Delivery Multimedia Integration Framework (DMIF). | |
| 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("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 Application 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) |
| Part 23 | ISO/IEC 14496-23 | Symbolic Music Representation (SMR) | (not yet finished - reached "FCD" stage in October 2006) |
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.
MPEG-4 contains patented technologies that require licensing in countries that acknowledge software patents. Patents covering MPEG-4 are claimed by over two dozen companies. The MPEG Licensing Authority[1] licenses patents required for MPEG-4 Part 2 Visual from a wide range of companies (audio is licensed separately) and lists all of its licensors and licensees on the site. New licenses for MPEG-4 System patents are under development[2] and no new licenses are being offered while holders of its old MPEG-4 Systems license are still covered under the terms of that license for the patents listed (MPEG LA – Patent List).
AT&T is trying to sue companies such as Apple Inc. over alleged MPEG-4 patent infringement.[3] The terms of Apple's Quicktime 7 license for users[4] describes in paragraph 14 the terms under Apple's existing MPEG-4 System Patent Portfolio license from MPEGLA.
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