MPEG-4

MPEG-4 builds upon the success and experience of MPEG-2. It is best known for:

• Lower bit-rates than MPEG-2 (for the same quality of video)
• Use of natural or synthetic objects that can be rendered together to make a scene
• Support for interactivity

For authors, MPEG-4 enables creating content that is more reusable and flexible, with better content protection capabilities.

For consumers, MPEG-4 can offer more interactivity and, due to the lower bit-rate over MPEG-2, the ability to enjoy content over new networks (such as DSL) and mobile products.

MPEG-4 is an ISO standard (ISO/IEC 14496).

MPEG-4 provides a standardized way to represent audio, video, or still image media objects using descriptive elements (instead of actual bits of an image, for example). A media object can be natural or synthetic (computer-generated) and can be represented independent of its surroundings or background.

It also describes how to merge multiple media objects to create a scene. Rather than sending bits of picture, the media objects are sent, and the receiver composes the picture. This allows:

• An object to be placed anywhere
• Geometric transformations on an object
• Grouping of objects
• Modifying attributes and transform data
• Changing the view of a scene dynamically

Audio Overview

MPEG-4 audio supports a wide variety of applications, from simple speech to multi-channel high-quality audio.

Audio objects (audio codecs) use specific combinations of tools to efficiently represent different types of audio objects. Profiles use specific combinations of audio object types to efficiently service a specific market segment. Levels specify size, rate, and complexity limitations within a profile to ensure interoperability.

Currently, most solutions support a few of the most popular audio codecs (usually AAC-LC and HE-AAC) rather than one or more profiles/levels.