Once it became possible to stream audio over the Internet, commercial radio stations got the idea of broadcasting their content over the Internet as well as over the air. Not so long after that, college radio stations started putting their signal out over the Internet. Then college students started their own radio stations. With current technology, virtually anyone can start a radio station. The whole area of Internet radio is very new and in a state of flux, but it is worth saying a little bit about.
There are two general approaches to Internet radio. In the first one, the programs are prerecorded and stored on disk. Listeners can connect to the radio station’s archives and pull up any program and download it for listening. In fact, this is exactly the same as the streaming audio we just discussed. It is also possible to store each program just after it is broadcast live, so the archive is only running, say, half an hour, or less behind the live feed. The advantages of this approach are that it is easy to do, all the techniques we have discussed work here too, and listeners can pick and choose among all the programs in the archive. The other approach is to broadcast live over the Internet. Some stations broadcast over the air and over the Internet simultaneously, but there are increasingly many radio stations that are Internet only. Some of the techniques that are applicable to streaming audio are also applicable to live Internet radio, but there are also some key differences.
One point that is the same is the need for buffering on the user side to smooth out jitter. By collecting 10 or 15 seconds worth of radio before starting the playback, the audio can be kept going smoothly even in the face of substantial jitter over the network. As long as all the packets arrive before they are needed, it does not matter when they arrived.
One key difference is that streaming audio can be pushed out at a rate greater than the playback rate since the receiver can stop it when the high-water mark is hit. Potentially, this gives it the time to retransmit lost packets, although this strategy is not commonly used. In contrast, live radio is always broadcast at exactly the rate it is generated and played back.
