HEAAC

HE-AAC, short for High-Efficiency Advanced Audio Coding, is a family of lossy audio coding standards developed under MPEG-4 Part 3. It extends AAC by adding techniques that improve coding efficiency at low to mid bitrates, allowing higher perceived audio quality at the same or lower bitrates. HE-AAC is also known as AAC+, and is commonly referred to in consumer devices and streaming services.

The original HE-AAC (often called HE-AAC v1) combines the AAC core with Spectral Band Replication (SBR). SBR encodes high-frequency content more efficiently by transmitting a lower-bandwidth representation and reconstructing the high frequencies on the decoder side. This enables better quality at nominal bitrates around 48 to 96 kbps. A later evolution, HE-AAC v2 (sometimes called Enhanced HE-AAC or AAC+DRA in some markets), adds Parametric Stereo (PS). PS encodes stereo information more efficiently by transmitting a monaural core plus side parameters to reconstruct stereo, further reducing bitrate for stereo content.

Technical overview: AAC provides the central codec, while SBR handles high-frequency extension to boost efficiency. PS in HE-AAC v2 adds stereo information at a low overhead, improving performance for stereo material without increasing bitrate substantially. Decoding HE-AAC requires a decoder with SBR (and PS, for v2) support; older AAC-LC-only decoders cannot properly reproduce HE-AAC content.

Applications and impact: HE-AAC and its v2 variant have been widely adopted for streaming, internet radio, mobile broadcasting, and digital multimedia players. They offer improved quality at lower bitrates compared with AAC-LC, contributing to efficient delivery of audio over bandwidth-constrained networks.