Online Radio Streaming Formats
Whilst radio is traditionally broadcast 'over the air' on one of the bandwaves, for quite a few years now, student radio stations have made use of the internet as either their primary broadcast platform, or in addition to a traditional AM frequency. Broadcasting online is relatively easy, and allows anyone in the world with access to a computer to listen to you - perfect for the parents of foreign students who live abroad. The internet is also unregulated, and so there are no licensing bodies you need to apply to just to be able to broadcast.
The internet wasn't really designed for delivering live media content though, and so a range of additional technologies have had to be developed in order for audio players to be able to download data and play it back in a way that seems live.
When I started at Rare FM (UCL), we had a Windows server providing a Windows Media Audio stream (WMA or ASF). The proprietary Windows streaming format is kinda useful in that most people tend to have PCs with a Windows operating system and Windows Media Player installed by default. This means that those people can listen to your station instantly, without having to install any additional software. However, as things have developed, there are now several different versions of both the player and the streaming format. Keeping track of which players support which versions is a bit of a nightmare. As I understand it, the WMA format is actually more of a 'container', within which all kinds of different codecs (streaming formats) might be employed.
The Windows formats also require a Windows server with propriatary software to host the streams, which all cost money, something student radio stations often don't have much of. With all this in mind, when it came the time at Rare FM to replace the server (the old one was constantly crashing), we went instead for a Linux server providing 'MP3 streams'.
MP3 streaming grew out of the popular MP3 format which was so revolutionary. Initially, Shoutcast was the most popular software package for serving MP3 streams, but there are now several open-source alternatives, including Icecast, which is what we used at Rare FM.
MP3 streams can be played by most popular media players, but compatibility with various versions of Windows Media Player is notoriously flaky. I remember getting lots of e-mails from listeners moaning that the stream would spend up to 10 minutes buffering in their version of WMP, before playing for a minute or so and then rebuffering again. The advice we used to give out to these people was simply to go and download Winamp instead.
There are other alternative formats available. Software company Real were one of the first to develop streaming audio formats and players. Their server software is expensive and highly propriatary, however, and so few student stations provide Real streams, URY being a notable exception. The slightly odd-sounding OGG Vorbis format was developed as an open-source alternative to MP3, which still has patents attached to it. The quality is meant to be better too, and more and more players now support this format. Several student radio stations provide an Ogg stream now, usually in addition to another format (eg IC Radio).
An additional consideration is how you provide access to the streams via your website. It's possible to embed a player within a web page, eg a pop-up window, using plugins installed in browsers. This has the advantage in that you can provide additional information around the player, such as links to other bits of your site. It's still worth providing a link direct to the stream though, in order to make it easy for people to listen using their normal player, if that's what they prefer.
Looking forward, there seem to be a few possible developments in online streaming. Surge seem to be fairly advanced in this, providing 'IPv6' streams and 'multicast' streams, which have the potential to reduce your server bandwidth by distributing the load across a wider network. I'm not sure I fully understand either of these technologies though, so I'll leave that to someone else to explain.
The SRA wiki has more information about web streaming, so if you're interested, read that too, and consider contributing to that page.