Unified Speech and Audio Coding

The MPEG-D USAC standard (ISO/IEC 23003-3) defines the Extended High Efficiency AAC profile, which contains all of the tools of the HE-AAC v2 profile plus the mono/stereo capabilities of the Baseline USAC profile. As a result, a decoder built according to the Extended High Efficiency AAC profile is able to also decode the bit streams created for the previous AAC family profiles. The Extended High Efficiency AAC profile was designed for applications relying on a consistent performance at low data rates while being able to decode all existing AAC-LC, HE-AAC and HE-AACv2 content. == xHE-AAC ==

Fraunhofer has defined the xHE-AAC codec as the combination of the Extended High Efficiency AAC profile and appropriate parts of the MPEG-D DRC Loudness Control Profile or Dynamic Range Control Profile. xHE-AAC extends the operating range of the codec from 12 to 300 kbit/s for stereo signals and allows seamless switching between bitrates over this range for adaptive bitrate delivery (using standards such as MPEG-DASH or HLS for example). xHE-AAC also includes MPEG-D DRC mandatory loudness control to playback content at a consistent volume and offers new dynamic range control profiles for listening in noisy situations. While xHE-AAC decoders will be able to decode the bit streams created for the previous AAC family profiles, xHE-AAC encoders are typically intended for encoding of MPEG-D USAC audio object type (AOT 42) with MPEG-D DRC loudness metadata, though some may support encoding legacy AAC object types. and is a trademark of Fraunhofer. In 2018, xHE-AAC was included in Via Licensing's AAC patent pool at no additional cost. In January 2021, Fraunhofer announced a test service and trademark program for xHE-AAC and announced that the codec is being used by Netflix. Netflix reported that users switched from speakers to headphones 16% less often (due to poor sound quality or inadequate volume) on high dynamic range content when using xHE-AAC instead of HE-AAC. Netflix also explained that xHE-AAC allowed them to begin streaming with adaptive audio bitrates to Android devices. Fraunhofer also announced xHE-AAC licenses to MainConcept, Poikosoft, and LG. xHE-AAC is supported by the Bento4 DASH/HLS packager. In January 2022, MainConcept established a web encoding service to test xHE-AAC. In October 2022, xHE-AAC decoding was added to Windows 11 and Xbox devices. Compatibility xHE-AAC is supported in Android since Android Pie and has been licensed to Microsoft. Playing xHE-AAC audio files is supported in foobar2000 from version 2.25 onwards. In October 2022, Windows 11 added support for xHE-AAC in the 22H2 update. == See also ==