The cook codec is a lossy

Lossy data compression

In information technology, "lossy" compression is a data encoding method that compresses data by discarding some of it. The procedure aims to minimize the amount of data that need to be held, handled, and/or transmitted by a computer...

 audio compression codec

Codec

A codec is a device or computer program capable of encoding or decoding a digital data stream or signal. The word codec is a portmanteau of "compressor-decompressor" or, more commonly, "coder-decoder"...

 developed by RealNetworks

RealNetworks

RealNetworks, Inc. is a provider of Internet media delivery software and services based in Downtown Seattle, Washington, United States. The company is the creator of RealAudio, a compressed audio format; RealVideo, a compressed video format; RealPlayer, a media player; RealDownloader, a download...

. It is also known as Cooker, Gecko, RealAudio G2, and RealAudio 8 low bitrate (RA8LBR).

Introduced in 1998, the cook codec was the first audio codec developed by RealNetworks in-house, and was named after its author, Ken Cooke. The design was largely based on G.722.1

G.722.1

G.722.1 is a licensed royalty-free ITU-T standard audio codec providing high quality, moderate bit rate wideband G.722.1 is a licensed royalty-free ITU-T standard audio codec providing high quality, moderate bit rate (24 and 32 kbit/s) wideband G.722.1 is a licensed royalty-free ITU-T standard...

. It is a pure transform codec based on the modified discrete cosine transform

Modified discrete cosine transform

The modified discrete cosine transform is a Fourier-related transform based on the type-IV discrete cosine transform , with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset,...

 with a single block size.

In 2003, RealNetworks introduced a surround sound

Surround sound

Surround sound encompasses a range of techniques such as for enriching the sound reproduction quality of an audio source with audio channels reproduced via additional, discrete speakers. Surround sound is characterized by a listener location or sweet spot where the audio effects work best, and...

 version of cook, called RealAudio Multichannel. This was initially designated by the four-character code 'whrl', but is now identified as 'cook', as mono/stereo files are.

Although RealNetworks never published a technical description of the cook codec, others have reverse engineered

Reverse engineering

Reverse engineering is the process of discovering the technological principles of a device, object, or system through analysis of its structure, function, and operation...

 the format, and as of December 2005, FFmpeg

FFmpeg

FFmpeg is a free software project that produces libraries and programs for handling multimedia data. The most notable parts of FFmpeg are libavcodec, an audio/video codec library used by several other projects, libavformat, an audio/video container mux and demux library, and the ffmpeg command line...

 libavcodec

Libavcodec

libavcodec is a free software/open source LGPL-licensed library of codecs for encoding and decoding video and audio data. Same name but incompatible libraries are provided from both FFmpeg project and Libav project....

 contains a decoder capable of playing cook-encoded files. As of July 2009, Rockbox

Rockbox

Rockbox is a replacement for the standard firmware in various forms of digital audio players . It offers an alternative to the player's operating system, in many cases without removing the original firmware, which provides a plug-in architecture for adding various enhancements and functions...

is capable of playing cook-encoded files as well.