While most audio codecs aim to solve specific problems—relatively high bit-rate music reproduction such as AAC and MP3, low latency voice reproduction such as Speex and the AMR family—Opus provides a "one size fits all" option which, according to its developers, provides best-in-class quality in almost all applications.
The codec was primarily developed by Mozilla and Xiph.org, with contributions from Skype/Microsoft and Broadcom. Opus weds Xiph.org's low-latency high bitrate music-oriented CELT algorithm to Skype's low bitrate speech-oriented SILK. The codec switches between algorithms depending on the bandwidth available, while boasting real-time latencies across the full bitrate/quality spectrum.
source : http://arstechnica.com/gadgets/2012/09/newly-standardized-opus-audio-codec-fills-every-role-from-online-chat-to-music/
