Icecast is a streaming media project released as free software maintained by the Xiph.org Foundation. It also refers specifically to the server program which is part of the project. Icecast was created in December 1998/January 1999 by Jack Moffitt and Barath Raghavan to provide an open source audio streaming server that anyone could modify, use, and tinker with. Alexander Haväng was also one of the chief architects of this product. Version 2 was started in 2001, a ground-up rewrite aimed at multi-format support (initially targeting OggVorbis) and scalability.
The Icecast server is capable of streaming audio content as Opus or Vorbis over standard HTTP, video as WebM or Theora over HTTP, MP3 over the communications protocol used by SHOUTcast, AAC, and NSV over the SHOUTcast protocol (Theora, AAC, and NSV are only supported in version 2.2.0 and newer). It requires external programs, called "source clients", to originate the streams, and the Icecast project includes a source client program known as IceS. The source runs typically in the place where the audio is generated (e.g., a studio) and the Icecast server in a place where a lot of bandwidth is available (e.g., a colocation centre). Since version 2.4.0 source clients can use plain HTTP standard PUT requests instead of the custom SOURCE method.