|
:''Not to be confused with MPEG-4 SLS, which is branded HD-AAC.'' High-Efficiency Advanced Audio Coding (HE-AAC) is an audio coding format for lossy data compression of digital audio defined as an MPEG-4 Audio profile in ISO/IEC 14496-3. It is an extension of Low Complexity AAC (AAC LC) optimized for low-bitrate applications such as streaming audio. HE-AAC version 1 profile (HE-AAC v1) uses spectral band replication (SBR) to enhance the compression efficiency in the frequency domain. HE-AAC version 2 profile (HE-AAC v2) couples SBR with Parametric Stereo (PS) to enhance the compression efficiency of stereo signals. It is a standardized and improved version of the AACplus codec. HE-AAC is used in digital radio standards like DAB+ and Digital Radio Mondiale. ==History== The progenitor of HE-AAC was developed by Coding Technologies under the trade name CT-aacPlus. CT-aacPlus combined MPEG-2 AAC LC with the Coding Technologies invented spectral band replication (SBR). CT-aacPlus is the codec used by XM Radio for their satellite radio service. Subsequently, Coding Technologies submitted their SBR to MPEG as a basis of HE-AAC. HE-AAC version 1 was standardized as a profile of MPEG-4 Audio in 2003 by MPEG and published as part of MPEG-4 in document ISO/IEC 14496-3:2001/Amd 1:2003. The HE-AAC version 2 profile was standardized in 2006 as ISO/IEC 14496-3:2005/Amd 2:2006.〔 A parametric stereo coding tool used in HE-AAC v2 was standardized in 2004 by MPEG and published in document ISO/IEC 14496-3:2001/Amd 2:2004. HE-AAC version 2 was also standardized under the name Enhanced aacPlus by 3GPP for 3G UMTS multimedia services in September 2004 (3GPP TS 26.401). It is based on the AAC LC, SBR and Parametric Stereo coding tools defined in the MPEG-4 Audio standard (and it refers to ISO/IEC 14496-3:2001/Amd.1:2003 - Bandwidth Extension, ISO/IEC 14496-3:2001/Amd.2:2004 - Parametric Coding for High Quality Audio, ISO/IEC 14496-3:2001 and ISO/IEC 14496-3:2001/Amd.1:2003/DCOR1). In addition it includes further tools such as error concealment, spline resampler, and stereo-to-mono downmix. It was also published by ETSI as TS 126 401 V6.1.0 in December 2004. Prior to the standardization of HE AAC v2 by MPEG, Coding Technologies submitted the combination of HE-AAC v1 coupled with Parametric Stereo under the name Enhanced AAC+. As a result, aacPlus v2 and eAAC+ are now common trade names that refer to HE-AAC v2. AAC+ and aacPlus are common trade names that refer to HE-AAC v1. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「High-Efficiency Advanced Audio Coding」の詳細全文を読む スポンサード リンク
|