High Quality Content by WIKIPEDIA articles! Constrained Energy Lapped Transform (CELT) is an open, royalty-free lossy audio compression format and a free software codec with especially low algorithmic delay for use in low-latency audio communication. The algorithms are openly documented and may be used free of software patent restrictions. Development of the format is maintained by the Xiph.Org Foundation (as part of the Ogg codec family) and is currently coordinated by the Opus working group of the Internet Engineering Task Force (IETF). The software library libcelt serves as the reference implementation for CELT, written in C and published as free software under Xiph`s own 3-clause BSD-ish license.