While there's no shortage of radio broadcasters on the Internet offering everything from m-funk to Bach, consistency is a bit harder to come by. No less than four different Web casting formats exist for Web casting with both live and recorded content from virtually every country and in every genre. The most popular are Real Networks' Real Audio format, Windows Media format, Ogg Vorbis and the m3u format which is based on the mp3 format. ?> ?>
Quality is of the utmost importance in considering any audio reproduction process, and Web casting is no different. The quality of a Web cast audio stream is determined by two main factors: the bitrate of the recording and the quality of the client's Internet connectivity to the server.
The bitrate of a recording describes how much computer data is used to represent the recorded sound. A bitrate of 24 kilobits per second, suitable for dialup users, means that for each second of audio recorded, twenty-four thousand ones and zeros are needed to store that sound on a computer. 24 kilobits per second may seem like a lot but the sound reproduced is only radio quality, while recordings at 128 kilobits per second or more--typical for mp3s--can reproduce almost CD-quality music. Streaming higher bitrate recordings requires more data to be transmitted, making them unsuitable for low-quality Internet connections.
With data compression available on all four formats, however, the actual number of bits stored on the computer or sent over the Internet may be reduced significantly with only slight loss of quality. This allows dial-up users with Internet connections effectively maxing out at under 60 kilobits per second to receive streams encoded at much higher bitrates.
Typically, larger servers will offer multiple streams at different bitrates, targeted to users with different connection speeds, while smaller home-brew servers on DSL or broadband connections will only offer a few low-bitrate slots.
Both the server and client Internet connections can be marginally improved by minimizing Web and other Internet traffic, or a better computer to manage, encode or decode audio streams while a faster Internet connection will provide the most benefit.
While all four formats can provide radio-quality audio over a standard dial-up connection, there are subtle but audible differences in the streamed audio because of the different encoding techniques. In general, Real Audio streams are cleaner but sound flatter than the other streams. Real Audio streams suffer the most from slow or erratic Internet connections, and take the most computing time to encode. Windows Media streams sometimes contain audible audio artifacts especially with fast or high-frequency tones and fare well with a bad connection but decoding suffers if the client computer is slow. m3u streams, being slightly modified mp3s, suffer from the same limitations as mp3s such as loss of subtle or quiet tones but is resilient when it comes to connection, data loss or lack of client computing resources. Despite being a work in progress, users have reported that Ogg Vorbis audio files have the highest fidelity to the original and streaming, once perfected, will be tolerant of flaky Internet connections.
In terms of the number of Web casters using streaming radio, m3u appears to be the most popular format for microcasters because of the available free and open-source server and client software, and the ability to broadcast existing mp3s without further encoding. Larger Web casters tend to use the Windows Media streaming format, with free server software and encoders from Microsoft for Windows server platforms. The Real Audio format, which pioneered and once dominated streaming media is falling into disuse largely because of compatibility issues with client software and the expensive server and encoding software required.
Smaller Web casters tend to favor the Open Source Icecast server and Nullsoft's SHOUTcast servers which are both free and stream the mp3 format. Source music for both can be mp3 files or encoded live using additional software. The Windows Media server, which offers dynamic connection rate adjustments and other features is less popular among personal Web casters as mp3s need to be converted to ASF, the Windows Media format, before streaming. The Ogg Vorbis format currently suffers from a similar limitation in that the free encoder remains in development and is slow compared to mp3 encoding, while encoding high-bitrate audio with the RealSystem Producer encoder software has been a consistently slow process.
On the client side, there's WinAmp, MacAmp and Windows Media player, all of which support the m3u and Windows Media formats but not Real Audio which is only supported by its own Real Player family of clients. Plugins for Ogg Vorbis are available for WMP and Quicktime and the format is supported natively in Sonique and FreeAmp for Windows.
Finding a radio stream is easy. With thousands of Web casters from around the world streaming umpteen genres 24 hours a day, 7 days a week, there's literally something for everybody. MacAmp has built-in online radio listings and search features, while the WinAmp radio site, SHOUTcast and IceCast sites have searchable listings. The Windows Media player integrates with listings at the Windows Media Web site but selection is comparably limited. The most comprehensive Real Media listings can be found at the Real site for those who use the non-free player.
In addition to streams by individuals and traditional radio stations, unauthorized radio streams are also available. Web casts of on-air-only stations such as CJSW and even police radio scanners can be found on public listings.