Internet radio technology
Streaming
One of the most common ways to distribute internet radio is via streaming technology using a lossy audio codec. The MP3 codec is most popular, followed by Ogg Vorbis, Windows Media Audio, and RealAudio; use of HE-AAC (sometimes called aacPlus) is gaining in popularity. The bits are "streamed" over a TCP/IP connection, then reassembled and played within about 2 seconds. Therefore, streaming radio has about a two-second lag time.
There are three major components to an audio stream:
Audio stream source
Audio stream repeater (server)
Audio stream playback
There are many methods for creating the audio stream source. Those more technologically savvy may opt for the SHOUTcast service, which utilizes Winamp and the SHOUTcast DSP plugin to deliver MP3 audio at higher bitrates. Other methods include open source technologies such as Streamcast, stream-db, IceS, and MuSE, and patent-free data formats such as Ogg Vorbis. Using open source stream source tools allows for interesting web interface possibilities like phpStreamcast.
Two of the most popular internet radio networks are Live365 and SHOUTcast. Open source alternatives include Icecast and Xiph.org, which include Ogg Vorbis streamings (that can be played by Winamp and Zinf). Collectively, these internet radio servers list thousands of Internet radio stations covering an ever-expanding variety of genres. The purpose of the server is to repeat the stream source to the audio playback software.
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Sites that aggregrate links of Internet radio broadcasts enable listeners to find internet broadcasts by genre, language, or location.
Some sort of audio playback software or hardware, that is capable of reading HTTP data streams, is needed to listen to streaming MP3 audio. Some popular software players are Winamp for Windows, iTunes for Macintosh and Microsoft Windows, and XMMS on Unix/Linux. Listening to internet radio through hardware devices has not been very popular in the past, due to the limited number of devices on the market, though the availability of such devices and their consumer popularity is expected to increase significantly during 2006. A list of commercially available devices is available at Internet radio device, but many of these are limited in which audio codecs they can use and consequently the variety of internet radio stations they are compatible with.
There is a tradeoff between audio quality and audience size. Stations that encode their streams at a lower bitrate have lower audio quality, but they are more accessible to listeners with a dialup connection, and they can serve more simultaneous users on a given upstream pipe.
There are also a small number of web radio programs that allow users to rate the songs they are listening to. This allows a user's music listening choices to be correlated against those of others, as with the programs iRATE radio, Last.fm, and Radio Paradise.
