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. It is a pure transform codec based on the modified discrete cosine transform with a single block size.
In 2003, RealNetworks introduced a surround sound 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 the format, and as of December 2005, FFmpeg libavcodec contains a decoder capable of playing cook-encoded files. As of July 2009, Rockbox is capable of playing cook-encoded files as well.