Opus is a totally open, royalty-free, highly versatile audio codec. Opus is unmatched for interactive
speech and music transmission over the Internet, but is also intended for storage and streaming
applications. It is standardized by the Internet Engineering Task Force (IETF) as RFC 6716
which incorporated technology from Skype’s SILK codec and Xiph.Org’s CELT codec.
Technology
Opus can handle a wide range of audio applications, including Voice over IP, videoconferencing,
in-game chat, and even remote live music performances. It can scale from low bitrate narrowband
speech to very high quality stereo music. Supported features are:
Bitrates from 6 kb/s to 510 kb/s
Sampling rates from 8 kHz (narrowband) to 48 kHz (fullband)
Frame sizes from 2.5 ms to 60 ms
Support for both constant bitrate (CBR) and variable bitrate (VBR)
Audio bandwidth from narrowband to fullband
Support for speech and music
Support for mono and stereo
Support for up to 255 channels (multistream frames)
Dynamically adjustable bitrate, audio bandwidth, and frame size
Good loss robustness and packet loss concealment (PLC)
Floating point and fixed-point implementation
You can read the full specification, including the reference implementation, in RFC 6716.
An up-to-date implementation of the Opus standard is also available from the downloads page.
This Opus 1.2-alpha alpha release
of the upcoming Opus 1.2 brings many quality improvements, new features, and bug fixes, including:
Speech quality improvements especially in the 12-20 kbit/s range
Improved VBR encoding for hybrid mode
More aggressive use of wider speech bandwidth, including fullband speech starting at 14 kbit/s
Music quality improvements in the 32-48 kb/s range
Generic and SSE CELT optimizations
Support for directly encoding packets up to 120 ms
DTX support for CELT mode
SILK CBR improvements
Support for all of the fixes in draft-ietf-codec-opus-update-04 (the mono downmix and the folding fixes need –enable-update-draft)
Many bug fixes, including integer overflows discovered through fuzzing (no security implications)
Please test it and and report any problems. There are no known regressions compared to the
latest stable release (1.1.3), but given the large number of changes, it’s possible some bugs have
slipped through.
Fixes encoder or decoder state reset, which would previously disable some run-time selected architecture-specific optimizations; and
Fixes hybrid mode discontinuous transmission (DTX) operation, where the comfort noise above 8 kHz was incorrectly estimated and could
oscillate in time.
None of these bugs were regressions over previous releases.
