Nero's AAC Encoder and Decoder Nero AAC reference quality MPEG-4 and 3GPP audio codec. Reference quality MPEG-4 audio codec, fully compatible with the latest version of the state-of-the-art MPEG-4 audio standard (LC-AAC, HE-AAC and HE-AAC v2). Note that this is a binary repackaging and not compiled from source.