Software design
The SHOUTcast software uses a client–server model, with each component communicating via a network protocol that intermingles audio or video data with metadata such as song titles and the station name. It uses HTTP as a transport protocol. Although multicast was planned, it was never developed.
SHOUTcast servers and clients are available for FreeBSD, Linux, Mac OS X, Microsoft Windows, and Solaris. Client-only versions exist for Android, BlackBerry OS, iOS (iPad, iPhone), Palm OS and webOS (Radio Hibiki), PlayStation Portable, Windows Mobile, Symbian S60 and UIQ, Nintendo DS (DSOrganize), and Wii.
The output format is supported by multiple clients, including Nullsoft's own Winamp as well as Amarok, Exaile, foobar2000, iTunes, Songbird, Totem, XMMS, and Zinf. If the client does not support the SHOUTcast protocol, then the SHOUTcast server sends the stream without the metadata thus allowing it to be heard/viewed in clients like Windows Media Player. SHOUTcast servers are usually linked to by means of playlist files, which are small text files (usually with extensions .pls or .m3u) that contain the URL of the SHOUTcast server. When that URL is visited in a Web browser which identifies itself as Mozilla-compatible (as most do), the server will return a generated SHOUTcast server info/status page, rather than streaming audio.
The most common use of SHOUTcast is for creating or listening to Internet audio broadcasts; however, video streams exist as well. Some traditional radio stations use SHOUTcast to extend their presence onto the Web.
Created in 1999, SHOUTcast's streaming protocol uses metadata tags and responses that all start with ICY, which stands for "I Can Yell."
A feature of SHOUTcast servers is the ability to optionally publish server information, including the current number of listeners, in a directory of stations that AOL maintains on the SHOUTcast website. Site visitors can pick a station to listen to and download a playlist file for use in their own SHOUTcast-capable media player.
In September 2008, AOL redesigned the SHOUTcast website, which had been roughly the same since 2000. In 2010, SHOUTcast again redesigned it with more of an AOL look. As part of the redesign, the directory and services were rebranded as "SHOUTcast Radio", rather than "SHOUTcast Streaming Technology." The redesign included a fully functional option to view the site and directory with the old layout.
VideoLAN says that AOL's license for use of the SHOUTcast Radio servers would “[force] us to integrate the spyware and adware based Shoutcast Radio Toolbar inside your browser.” and thus prevents open source software from using the SHOUTcast Radio servers. VideoLAN therefore removed support for SHOUTcast Radio in version 1.1 of the VLC media player, and pointed users to the Icecast directory instead. Only access to the directory of SHOUTcast stations was removed, not the ability to play SHOUTcast streams.
As of 2011, up to 900,000 concurrent listeners can be seen during peak hours, according to SHOUTcast's self-reported statistics. The maximum and minimum number of listeners fluctuates widely during a day, with roughly three times the number of listeners during peak hours compared to low use times. As of July 2011, SHOUTcast Radio includes over 45,000 stations.
Concurrent listener growth
Concurrent server growth
