You should realize that those pages are not designed fur us geeks to extract the URL. When we do and play trough mplayer you miss all those nice advertisements. If you don't look at the advertisements you are not entitled to listen to the music. Finding the URL requires some hacking. Not all sites are equal, and many have a different way to embed the URL.
Now this station plays my top favorite exercising music, so I put in the effort to find the URL for my own benefit.
This time I right-clicked on the Play button and asked for
inspect element. (This was opera, but I think the menu item is the same in Firefox). This doesn't show the page source as it is downloaded (which you see with
View Source). Instead it shows exactly what is being executed by the browser engine.
In this case, it was Flash Player, playing this URL:
http://icecast5.play.cz/radio-zlatka128.mp3
It plays wonderfully in mplayer!
jlinkels