INTERNATIONAL ORGANISATION FOR STANDARDISATION
ORGANISATION INTERNATIONALE DE NORMALISATION
ISO/IEC JTC1/SC29/WG11
CODING OF MOVING PICTURES AND AUDIO
ISO/IEC JTC1/SC29/WG11 N2670
March 1999 / Seoul, Korea
| This web page is intended to provide an overview of the "MPEG-4 Audio Version 2 Committee Draft 14496-3" and is based on excerpts from this document. The complete document is available by ftp. |
MPEG-4 version 2 is an amendment to MPEG-4 version 1. This document contains the description of bitstream and decoder extractions related to new tools defined within MPEG-4 version 2. As long as nothing else is mentioned, the description made in MPEG-4 version 1 is not changed but only extended.
ISO/IEC 14496-3 (MPEG-4 Audio) is a new kind of audio standard that integrates many different types of audio coding: natural sound with synthetic sound, low bitrate delivery with high-quality delivery, speech with music, complex soundtracks with simple ones, and traditional content with interactive and virtual-reality content. By standardizing individually sophisticated coding tools as well as a novel, flexible framework for audio synchronization, mixing, and downloaded post-production, the developers of the MPEG-4 Audio standard have created new technology for a new, interactive world of digital audio.
MPEG-4, unlike previous audio standards created by ISO/IEC and other groups, does not target a single application such as real-time telephony or high-quality audio compression. Rather, MPEG-4 Audio is a standard that applies to every application requiring the use of advanced sound compression, synthesis, manipulation, or playback. The subparts that follow specify the state-of-the-art coding tools in several domains; however, MPEG-4 Audio is more than just the sum of its parts. As the tools described here are integrated with the rest of the MPEG-4 standard, exciting new possibilities for object-based audio coding, interactive presentation, dynamic soundtracks, and other sorts of new media, are enabled.
Since a single set of tools is used to cover the needs of a broad range of applications, interoperability is a natural feature of systems that depend on the MPEG-4 Audio standard. A system that uses a particular coder - for example, a real-time voice communication system making use of the MPEG-4 speech coding toolset - can easily share data and development tools with other systems, even in different domains, that use the same tool - for example, a voicemail indexing and retrieval system making use of MPEG-4 speech coding. A multimedia terminal that can decode the Main Profile of MPEG-4 Audio has audio capabilities that cover the entire spectrum of audio functionality available today and in the future.
The remainder of this clause gives a more detailed overview of the capabilities and functioning of MPEG-4 Audio extended tools.
Several tools are provided to increase the error resilience for AAC. These tools increase the perceptual audio quality of the decoded audio signal in presence of noisy transmission channels.
The low delay coding functionality provides the ability to extend the usage of generic low bitrate audio coding to applications requiring a very low delay of the encoding / decoding chain (e.g. full-duplex real-time communications).
To allow for user on a remote side to dynamically control the streaming of the server, backchannel streams carrying user interaction information are defined.
The BSAC tool provides fine grain scalability. This tool takes information from bitstream demultiplexer, parses that information, decodes the Arithmetic coded bit-sliced data, and reconstructs the quantized spectra and the scalefactors.
MPEG-4 parametric audio coding uses the HILN technique (Harmonic and Individual Line plus Noise) to code non-speech signals like music at bit rates of 4 kbit/s and higher using a parametric representation of the audio signal. HILN allows independent change of speed and pitch during decoding. Furthermore HILN can be combined with MPEG-4 parametric speech coding (HVXC) to form an integrated parametric coder covering a wider range of signals and bit rates.
The EP tool provides unequal error protection. This tool receives several classes of bits from the audio coding tools, and then apply the forward error correction codes (FEC) and/or cycric redundancy code (CRC) for each class, according to the error sensitivity of it.
To be provided
| Location | Notes |
|---|---|
| w2670.pdf | Cover page of ISO/IEC 14496-3 PDAM document. |
| w2670_n.pdf | Normative part of ISO/IEC 14496-3 PDAM document. |
| w2670_i.pdf | Informative part of ISO/IEC 14496-3 PDAM document. |
Heiko Purnhagen 23-Jul-1999