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Chapter 11. General Audio Coding > MPEG-4 Additions to AAC

11.3. MPEG-4 Additions to AAC

Besides the building blocks provided by MPEG-2 AAC, the MPEG-4 T/F coder includes several extensions in order to enhance coding efficiency and offer new functionalities. Examples of additional building blocks include perceptual noise substitution (PNS), long-term prediction (LTP), and the transform-domain weighted interleave vector quantization (TwinVQ) coding kernel. The low-delay AAC (AAC-LD) coder and the error-resilience (ER) provisions illustrate how new functionalities can be supported by variation/modification of the basic AAC technology. The capability for scalable audio coding deserves particular attention in the context of MPEG-4 (see Section 11.4). Scalability is achieved by introducing concepts of large-step scalable coding into the AAC coding framework, resulting in a flexible toolboxlike solution that combines coding elements with different characteristics into a single, unified framework. Alternatively, the fine grain scalability (FGS) mode based on bit-sliced arithmetic coding (BSAC) may be used.

Although some of these extensions were added only in the 1st Amendment to MPEG-4 Audio Version 1 (the so-called Version 2 [MP4V2-3]), such as ER provisioning, low-delay T/F coding, and the BSAC scalability mode, no distinction will be made between Version 1 and Version 2 tools in the following discussions.


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