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

  • Version 1.1.2 released

    12 January, 2016

    This Opus 1.1.2 release fixes two bugs:

    • Resetting the encoder or decoder state with OPUS_RESET_STATE would disable some run-time selected architecture-specific optimizations; and
    • In hybrid mode discontinuous transmission (DTX) operation, the comfort noise above 8 kHz was incorrectly estimated and could oscillate in time.
    None of these bugs were regressions over previous releases. The code is available from the downloads page.

  • Version 1.1.1 released

    26 November, 2015

    This Opus 1.1.1 release brings many optimizations to the encoder and decoder, including:

    • x86 SSE, SSE2 and SSE4.1 intrinsics optimizations with run-time CPU detection contributed by Cisco Systems,
    • MIPS intrinsics optimizations contributed by Imagination Technologies,
    • ARM Neon optimizations contributed by Linaro and ARM,
    • many architecture-independent optimizations and memory footprint reductions that should improve performance on all platforms, and
    • several minor bug fixes.
    The quality of the encoder should be mostly unchanged compared to version 1.1. The code is available from the downloads page.

  • Version 1.1.1-rc released

    28 October, 2015

    The is a release candidate for the upcoming 1.1.1. This release includes further ARM optimizations. The quality should again be unchanged. downloads page.

  • Version 1.1.1-beta released

    15 October, 2014

    The is a beta release for the upcoming 1.1.1. This release focuses on code optimizations, especially on x86, MIPS and ARM. The quality should be unchanged. downloads page.

  • Version 1.1 released

    5 December, 2013

    After more than two years of development, we have released Opus 1.1. This includes:

    • new analysis code and tuning that significantly improves encoding quality, especially for variable-bitrate (VBR),
    • automatic detection of speech or music to decide which encoding mode to use,
    • surround with good quality at 128 kbps for 5.1 and usable down to 48 kbps, and
    • speed improvements on all architectures, especially ARM, where decoding uses around 40% less CPU and encoding uses around 30% less CPU.
    These improvements are explained in more details in Monty's demo (updated from the 1.1 beta demo).

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