Delay-reduced mode of MPEG-4 enhanced low delay AAC (AAC-ELD)

The MPEG-4 AAC Enhanced Low Delay (AAC-ELD) coder is well established in high quality communication applications, such as Apple's FaceTime, as well as in professional live broadcasting. Both applications require high interactivity, which typically demands an algorithmic codec delay between 15 ms and 35 ms. Recently, MPEG finalized a new delay-reduced mode for AAC-ELD featuring only a fraction of the regular algorithmic delay. This mode operates virtually at higher sampling rates while maintaining standard sampling rates for I/O. Supporting this feature, AAC-ELD can address even more delay critical applications, like wireless microphones or headsets for TV. In this paper, main details of the delay-reduced mode of AAC-ELD are presented and application scenarios are outlined. Audio quality aspects are discussed and compared against other codecs with a delay below 10 ms.