Opus or Opus Audio Codec is a lossy audio compression format developed by the Internet Engineering Task Force (IETF) that is particularly suitable for interactive real-time applications over the Internet. As an open format standardized through RFC 6716, a reference implementation is provided under the 3-clause BSD license. All known software patents which cover Opus are licensed under royalty-free terms.
Opus incorporates technology from two codecs: the speech-oriented SILK and the low-latency CELT.[3] Opus can be adjusted seamlessly between high and low bitrates, and internally, it transitions between a linear prediction codec at lower bitrates and a transform codec at higher bitrates (as well as a hybrid for a short overlap).
Opus has a very low algorithmic delay (22.5 ms by default), which is a necessity for use as part of a low audio latency communication link, which can permit natural conversation, networked music performances, or lip sync at live events. Opus permits trading-off quality or bitrate to achieve an even smaller algorithmic delay, down to 5 ms. Its delay is very low compared to well over 100 ms for popular music formats such as MP3, Ogg Vorbis and HE-AAC; yet Opus performs very competitively with these codecs in terms of quality per bitrate.[5] Unlike Ogg Vorbis, Opus does not require the definition of large codebooks for each individual file, making it preferable to Vorbis for short clips of audio.
Further information and deeper analysis: Opus on wikipedia
