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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 1.4
   
   Apr 20, 2023
   
   This Opus 1.4 major release brings the following improvements and fixes:
   
    * Improved tuning of the Opus in-band FEC (LBRR). See the issue for details
    * Added a OPUS_SET_INBAND_FEC(2) option that turns on FEC, but does not
      force SILK mode (FEC will be disabled in CELT mode)
    * Improved tuning and various fixes to DTX
    * Added Meson support, improved CMake support In addition to the
      improvements above, this release includes many minor bug fixes.
   
   Additionally, we have begun experiments on upcoming neural packet loss
   concealment and deep redundancy (DRED) features. Although not included in
   this release, you can see two IETF drafts describing the proposed extension
   and redundancy mechanisms. The code is also available on this development
   branch.
   
   Source code: opus-1.4.tar.gz
   
   --------------------------------------------------------------------------------


 * OPUSFILE 0.12
   
   Jun 27, 2020
   
   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 v0.11 release:
   
    * Fix stack overflow buffering out-of-sequence streams.
    * Fix possible divide-by-zero.
    * Fix issues with seeking in the win32 backend.
    * Fix an issue where the seek algorithm could be confused by stream data
      changing between reads.
    * Clean up compiler and scan-build warnings.
    * Avoid use of the deprecated ftime() function which has Y2038 problems.
    * Remove undefined behaviour memcpy(NULL) in op_read_native().
    * Visual Studio project files updated for libogg 1.3.4 library name change.
    * Various build systems updates.
    * Various integration and testing environment improvements.
   
   This release is backward-compatible with the previous release. We recommend
   all users upgrade.
   
   Note that because of the removal of certificate store hooks in openssl 1.1.1
   and later, there are unfortunately no supported versions of that library
   which can be used with the code in opusurl to validate https responses
   against the system certificate store on Windows. Using the system default
   access to the certificate store on other platforms works fine.
   
   Source code: opusfile-0.12.tar.gz, opusfile-0.12.zip.
   
   SHA-256 checksums:
   
   118d8601c12dd6a44f52423e68ca9083cc9f2bfe72da7a8c1acb22a80ae3550b  opusfile-0.12.tar.gz
   7f44575596b78d7787c1865b9653e2a71546ff1ae77d87c53ab16dcc7af295ba  opusfile-0.12.zip
   
   
   No Windows build is available for this release. Developers should integrate
   the source code directly into their applications.
   
   Programming documentation is available in tree and online.
   
   The library is functional, but there are likely issues we didn’t find in our
   own testing. Please give feedback in #opus on irc.libera.chat, opus@xiph.org,
   or at gitlab.
   
   --------------------------------------------------------------------------------


 * LIBOPUS 1.3.1
   
   Apr 12, 2019
   
   This Opus 1.3.1 minor release fixes an issue with the analysis on files with
   digital silence (all zeros), especially on x87 builds (mostly affects 32-bit
   builds). It also includes two new features:
   
    * A new OPUS_GET_IN_DTX query to know if the encoder is in DTX mode (last
      frame was either a comfort noise frame or not encoded at all)
    * A new (and still experimental) CMake-based build system that is eventually
      meant to replace the VS2015 build system (the autotools one will stay).
   
   Source code: opus-1.3.1.tar.gz
   Win32 binaries: opus-tools-0.2-opus-1.3.1.zip
   
   --------------------------------------------------------------------------------


 * LIBOPUS 1.3
   
   Oct 18, 2018
   
   This Opus 1.3 major release again brings quality improvements, new features,
   and bug fixes. You can read all the details in this release demo page.
   Changes since 1.2.x include:
   
    * Improvements to the VAD and speech/music classification using an RNN
    * Support for ambisonics coding using channel mapping families 2 and 3
    * Improvements to stereo speech coding at low bitrate
    * Using wideband encoding down to 9 kb/s
    * Making it possible to use SILK down to bitrates around 5 kb/s
    * Minor quality improvement on tones
    * Enabling the spec fixes in RFC 8251 by default
    * Security/hardening improvements
   
   Notable bug fixes include:
   
    * Fixes to the CELT PLC
    * Bandwidth detection fixes
   
   Source code: opus-1.3.tar.gz
   Win32 binaries: opus-tools-0.2-opus-1.3.zip
   
   --------------------------------------------------------------------------------

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