Wikipedia
AAC-LD
The MPEG-4 Low Delay Audio Coder (aka AAC Low Delay, or AAC-LD) is audio compression standard designed to combine the advantages of perceptual audio coding with the low delay necessary for two-way communication. It is closely derived from the MPEG-2 Advanced Audio Coding (AAC) standard. It was published in MPEG-4 Audio Version 2 ( ISO/ IEC 14496-3:1999/Amd 1:2000) and in its later revisions.