Opus is an open and royalty-free lossy audio compression format developed by the IETF and made especially suitable for interactive real-time applications over the Internet. Opus incorporates technology from the speech-oriented SILK codec and the low-latency CELT codec. Publication as an RFC is expected within the next few weeks. Opus can seamlessly scale to high and low bitrates and can transition 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 very low algorithmic delay compared to popular music formats such as MP3, Vorbis, and HE-AAC, and yet performs very competitively with them in terms of quality per bitrate. Also unlike these codecs, Opus does not require the definition of large codebooks for each individual file, making it also preferable for short clips of audio.
As Firefox has added support for the new Opus audio format, I am going to add Opus audio encoder in next release of MediaCoder. Stay tuned!