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—The CELT codec has been merged into the IETF Opus codec and is now obsolete—


  • Version 0.11.0 and 0.11.1 released

    15 February, 2011

    CELT 0.11.0 (originally not announced) and 0.11.1 has been released with a focus on freezing the bit-stream and updating the API. The bit-stream is now in "soft-freeze" state meaning there is an attempt to keep it fixed, but some bugs may force changes. Version 0.11 includes some minor quality improvements, mostly at high bit-rate. In version 0.11.1, some minor changes to the bit-stream were necessary to address two minor bugs in 0.11. The quality should improve (very) slightly, but not enough to be noticeable in most cases. Several Opus-related bugs have also been fixed.

  • Version 0.10.0 released

    21 December, 2010

    CELT 0.10.0 has been released with a focus on quality improvements. The bit-stream is not compatible with version 0.9.x. See Monty's CELT demo page for more details on recent (and less recent) CELT development.

  • Version 0.9.1 released

    8 November, 2010

    CELT 0.9.1 greatly improves the packet loss concealment. This change is especially dramatic in fixed point mode. The bit-stream is compatible with 0.9.0.

  • Version 0.9.0 released

    6 November, 2010

    CELT 0.9.0 mainly focuses on quality improvements. The transient handling code has been greatly improved and high-frequency artefacts have been reduced. There have also been lots of small improvements from better tuning of various parameters.

  • Version 0.8.1 released

    8 July, 2010

    CELT 0.8.1 fixes some bugs introduced in 0.8.0. The bit-stream remains compatible with 0.8.0, with the caveat that CELT no longer supports frame sizes that have prime factors larger than 5. This should not affect any reasonable application.

  • Version 0.8.0 released

    2 July, 2010

    Version 0.8.0 has been released, with improvements for high bit-rates and for transients in general. It also adds the possibility of changing the frame size dynamically, which requires a minor change in the API. At last, the new PLC algorithm from 0.7.1 is now enabled for the fixed-point builds as well. Version 0.8.0 is not bit-stream compatible with previous releases.

  • Version 0.7.1 released

    20 January, 2010

    Version 0.7.1 has been released, with improvements to the packet loss concealment (PLC). It is the first release not to break bit-stream compatibility with the previous release (0.7.0). But I promise not to do it again, the next CELT release will likely break compatibility once again.

  • Version 0.7.0 released

    26 October, 2009

    Version 0.7.0 has been released, with improvements to the stereo and low birate audio quality. API is incompatible with previous releases.

  • Version 0.6.1 released

    13 July, 2009

    Version 0.6.1 has been released, with improvements to the stereo mode. The mono mode is not affected.

  • Version 0.6.0 released

    4 July, 2009

    Version 0.6.0 has just been released, with many quality improvements, including better stereo coupling, better handling of transients, and better handling of highly tonal signals. In addition, packet loss robustness has been improved through the optional use of independent (intra) frames. CELT now supports a larger dynamic range, suitable for encoding 24-bit audio (float version only). There is also a very early VBR implementation.

  • Compatibility version released

    12 May, 2009

    This is a bugfix update of the compatability release with several bugfixes backported into the 0.5.1 compatability branch. As with, this release is not compatible with either 0.5.0 or earlier, or with 0.5.2 and later.

  • Compatibility version released

    22 April, 2009

    This is an update of the previous 0.5.1 prerelease; as several software and hardware projects have seen fit to deplot this prerelease version for development and testing, we've released this new version that changes the installation namespace from 'celt' to 'celt051' to ease installation and parallel development with other versions of celt without conflict. Aside from renaming symbols and install locations to 'celt051' there are no other changes from the celt 0.5.1 release. As with other CELT prereleases, this release is not compatible with either 0.5.0 or earlier, or with 0.5.2 and later.

  • Version 0.5.2 released

    17 February, 2009

    Version 0.5.2 has just been released with a few fixes over 0.5.1. On top of that, the pitch prediction was both improved and simplified. The other main change is a new bit allocation algorithm with better rounding and fine energy allocation.

  • Version 0.5.1 released

    17 December, 2008

    Version 0.5.1 is out. This release fixes a number of issues with 0.5.0. Several cases where the encoder could fail have been fixed, including one that could cause memory corruption (and possibly a segfault). In addition, the VQ search has been improved, which results in a small CPU reduction, while fixing some quality problems with low frequency tones. Other than that, there should be no significant quality changes.

  • Version 0.5.0 released

    10 October, 2008

    Version 0.5.0 is out. This release includes simplifications to the bit allocation code and includes a new low-complexity mode that can be enabled (without breaking compatibility) on the encoder side. There are several other optimisations and bug fixes included. The API has also been slightly modified, so code using CELT will have to be updated (minor).

  • Version 0.4.0 released

    26 July, 2008

    Version 0.4.0 is out. This release should greatly improve the handling of transients and reduce the amount of pre-echo, especially for larger frame sizes. There is now support for frame sizes up to 512 samples for those who don't have extreme delay requirements. The release also brings improved tuning for stereo and a variety of frame sizes and higher bit-rates. The API has been changed slightly to remove the overlap parameter, which is now automatically selected based on the frame size.

  • Version 0.3.2 released

    16 May, 2008

    Version 0.3.2 is out. This consists mainly of quality tuning. We've also completed some listening tests based on that version for the Comparison page.

  • Version 0.3.1 released

    26 April, 2008

    Version 0.3.1 is now released. CELT is now a lot faster and can run in real-time on a PC with less than 10% CPU.

  • Domain is up

    18 March, 2008

    Just registered celt-codec.com and celt-codec.org for this project. Now working on the website

—The CELT codec has been merged into the IETF Opus codec and is now obsolete—