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Information about MDN's MP3 Audio

Two PCs are being used for MDN's MP3 streaming with standard MS operating systems.

For the live audio streams from the House and Senate, the encoder is WinAmp, using special DLL plugins you can get from Shoutcast (the makers of WinAmp) for doing live MP3 streaming. With these plugins, WinAmp performs functions:

1. It takes the live audio signal (connected to the sound card's line in) and converts the sound to MP3 (Version 2.5 Layer III).
2. Then, it takes the MP3 digital signal and transmits that through a TCP/IP port to the audio server.

The Audio server is Shoutcast. A separate server runs for each of our audio streams -- the House, Senate and (at one time) Missouri Capital Caucus.

Because there is no file extension for the streaming audio location, it is not possible to put into a web page a direct link to the audio server. A browser would not know what to do with the stream. Instead, a link to an intermediary "play-list" file is used with the extension .M3U or .PLS (e.g HOUSE.PLS). That file contains nothing more than the URL of the audio stream and, sometimes, a bit more information about the feed. The only purpose is to have a special file extension that your browser understands is an MP3 stream that requires loading an MP3 player.

If you have installed your MP3 player correctly, your browser knows to use your MP3 player for any files with the .PLS extension. The MP3 player, like WinAmp, will open up the file, extract the IP address and port from the file and then make the streaming-audio connection.

All of the MP3 encoding and server software we are using is free. And, we've found, is fairly easy to set up. In fact, if you would like, you can take an audio stream from our House or Senate session and use it as the source for your own audio server.

Microsoft's Media Player, unfortunately, does not recognize PL3 files. For Media Player to work, you need to enter the address of the actual audio stream.

Fortunately, the latest browsers and operating systems make it possible to directly connect your browser to the audio stream without worrying about the technical details.

If you would like to set up your own audio server, check out:

• Icecast which is the MP3 server we are using. It is an open source code project, which means that not only is the software free, but that the source code is available.
• Shoutcast which is another free MP3 server.
• WinAmp which serves both an MP3 player and the encoder for our live MP3 audio -- the program that takes an analog audio source and converts it to a stream of MP3 digital audio.