Your source URL is made up of the IP address (or hostname) and port of your stream and looks like this:
http://[domain]:[port]
OR
http://[ip]:[port]
If you're using CentovaCast, you can find this URL by logging in to Centova, then choosing "Quick Links" on the left. Your source URL is the same thing as "Your streaming server index page", the second link from the top.
If you're using an IceCast server rather than ShoutCast, you may need to append your mount point to the end:
http://[domain]:[port]/mountpoint
If your player does not function in some browsers when using one of those URLs, try appending "/;" to the stream so it looks like this:
http://[domain]:[port]/;