At present, liveCaster can get its MP3 input from one of three sources:
So, to multicast live audio, you'll need to use input source 2 or 3. And, of course, you'll need a MP3 encoder to generate the live MP3 stream to begin with.
If your MP3 encoder can output its MP3 data to 'standard output', then you can simply pipe this into liveCaster (using its "-s stdin" option) - i.e., input source 2. This is the most efficient method, if you can do it.
An alternative is to set up a HTTP server for your data, and have liveCaster stream from this - i.e., input source 3. I.e., use liveCaster's "-s http://..." option. One benefit of this approach is that you can use liveCaster to stream to multicast-connected clients, but use the HTTP server to stream (unicast) to non-multicast-connected clients (if you have sufficient outgoing bandwidth, of course).
Two sets of tools for encoding and serving MP3 audio via HTTP are: