- Company: Xiph, IETF
- Extension: .opus
- Specification (codec): https://tools.ietf.org/html/rfc6716
- Specification (Ogg encapsulation): https://tools.ietf.org/html/draft-terriberry-oggopus-01
- Reference implementation: http://www.opus-codec.org/downloads/
Open standard for low-latency, scalable lossy audio coding based on the speech-oriented SILK codec and the low-latency CELT codec. Opus can transition between a linear prediction codec at low bitrates and a transform codec at high bitrates and supports a hybrid mode for a small bitrate range. Opus defaults to a latency that's 1/10th that of earlier music codecs (20ms vs. 200ms), making it possible for use in VoIP, and yet performs better in listening tests.
Note that Opus does not exceed the performance of CELT for music at bitrates over 75 kbit (http://www.hydrogenaudio.org/forums/index.php?showtopic=97913&st=0) which means that the unconditional merge of CELT into OPUS doubled the amount of code to be present, even for applications which do not benefit from the addition.