MPEG-4MPEG-4 (1998) is the designation for a group of audio and video coding standards agreed upon by MPEG (Motion Pictures Coding Experts Group). MPEG-4 is primarily designed to handle low bit-rate content, from 4800 bit/s to approximately 4 Mbit/s. The primary uses for the MPEG-4 standard are web (streaming media) and CD distribution, conversational (videophone) uses, and broadcast television.
MPEG-4 absorbs many of the features of MPEG-1 and MPEG-2, adding new features such as (extended) VRML support for 3D rendering, object-oriented oriented composite files (including audio, video and VRML objects), support for Digital Rights Management and various types of interactivity.
Most of the 'features' included in MPEG-4 are left to individual developers to implement. This means that there are very few complete implementations of the MPEG-4 standard. Anticipating this, the developers added the concept of 'Profiles', allowing various capabilities to be grouped together.
MPEG-4 consists of several standards (termed "Layers"), as follows:
Layer 1: Describes synchronization and multiplexing of video and audio.
Layer 2: Compression codec for video signals.
Layer 3: Compression codec for perceptual coding of audio signals.
Layer 4: Describes procedures for testing compliance.
Layer 5: Describes systems for Software simulation.
Layer 6: Describes Delivery Multimedia Integration Framework (DMIF)