CELT (Constrained Energy Lapped Transform) is an open,
royalty-free audio compression format and a
free software codec for use in
low-latency audio communication. It's a
lossy codec, meaning quality is permanently degraded to reduce file size.
CELT is meant to bridge the gap between
Vorbis and
Speex for applications where both high quality audio and low delay are desired.
[Xiph.Org , Retrieved 2009-09-01] It is suitable to carry both speech and music. It borrows ideas from
CELP codec, but avoids some of its limitations by working only with a
frequency of a sound.
In December 2007, a first development version of CELT was published. The latest version of CELT is 0.7.0, released on October 26, 2009.
On July 13, 2009 CELT Codec has been submitted as an IETF draft.
[[https://datatracker.ietf.org/drafts/draft-valin-celt-codec/ CELT IETF draft]] In May 2009, a draft of
RTP payload format for the CELT Codec was published.
Technical details
CELT can use
sampling rates from 32 kHz to 48 kHz and above, adaptive
bit-rate from 32 kbit/s to 128 kbit/s per channel and above. CELT supports mono and stereo and it is applicable to both speech and music. It uses ultra-low algorithmic delay (as low as 2 ms; scalable, typically from 3 to 9 ms).
There are no known intellectual property issues and it is free software/open-source.
Software
In January 2009 support for CELT was added to the
Ekiga and
FreeSWITCH VOIP programs.
CELT is also supported or used by:
- Mumble (starting with version 1.2)
See also
