Opus Interactive Audio Codec
Overview
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.
News
- libopus 1.3-beta
Dec 21, 2017
This Opus 1.3-beta beta release of the upcoming Opus 1.3 includes:
- Enabling by default the spec fixes in RFC 8251
- Improvements to the VAD and speech/music classification using an RNN
- Improvements to stereo speech coding at low bitrate
- Added support for ambisonics projection using mapping 3 (disabled by default)
- Fixes to the CELT PLC
Additionally, as a way to test the upcoming update to opus-tools, we’re providing Windows binaries built with 1.3-beta. These binaries are based on libopusenc, which means opusenc is finally able to make use of the Opus delayed-decision feature to make better speech/music transitions.
Source code: opus-1.3-beta.tar.gz
Win32 binaries (experimental): opus-tools-test1.zip
- libopusenc 0.1.1
Nov 13, 2017
This release fixes a few bugs in libopusenc 0.1, including the sample-accurate handling at the end of files. It also fixes crashes in a few use cases.
Source code: libopusenc-0.1.1.tar.gz
- opusfile 0.9
Aug 3, 2017
The opusfile library provides seeking, decode, and playback of Opus streams in the Ogg container (.opus files) including over http(s) on posix and windows systems.
opusfile depends on libopus and libogg. The included opusurl library for http(s) access depends on
opusfile and openssl.
Changes since the v0.8 release:
- Fix an invalid free with tag handling.
- Improve handling of corrupt streams.
- Improve performance on streams with many chain segments.
- Improve TLS host validation.
- Align op_raw_total to work better with op_raw_seek.
- Documentation and build improvements.
This release is backward-compatible with the previous release. We recommend all users upgrade.
The library is functional, but there are likely issues we didn’t find in our own testing. Please give feedback in #opus on irc.freenode.net or at opus@xiph.org.
Programming documentation is available in tree and online.
Source code: opusfile-0.9.tar.gz, opusfile-0.9.zip Windows build: opusfile-v0.9-win32.zip
- libopus 1.2.1
Jun 26, 2017
This Opus 1.2.1 minor release fixes a relatively rare issue where the 1.2 encoder would wrongly assume a signal to be bandlimited to 12 kHz and not encode frequencies between 12 and 20 kHz. This only happens on a few clips, but it is good to update to avoid a potential loss of quality.
There are no other changes compared to 1.2. Please report any problems.
Source code: opus-1.2.1.tar.gz
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