IceS is a source client for a streaming server. The purpose of this client is to provide an audio stream to a streaming server such that one or more listeners can access the stream. With this layout, this source client can be situated remotely from the icecast server.
The primary example of a streaming server used is Icecast 2, although others could be
used if certain conditions are met.
IceS 2.x supports sending an Ogg Vorbis stream to an Icecast server.
For MP3 support you may want to take a look at IceS 0.x.
Documentation for IceS 2 can be found here.