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:
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:
|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.
AT&T is trying to sue companies such as Apple Inc. over alleged MPEG-4 patent infringement. The terms of Apple's Quicktime 7 license for users describes in paragraph 14 the terms under Apple's existing MPEG-4 System Patent Portfolio license from MPEGLA.