non hai realizzato il player...
al posto di

codice:
player = Manager.createPlayer(url_media); // Creiamo il player 
player.realize();
usa il metodo createRealizedPlayer(...)

http://java.sun.com/products/java-me...les/index.html

questo è un piccolo esempio

codice:
import java.applet.*; 

import java.awt.*; 

import java.net.*; 

import javax.media.*; 

  

public class PlayerApplet extends Applet { 

Player player = null; 

public void init() { 

setLayout( new BorderLayout() ); 

String mediaFile = getParameter( "FILE" ); 

try { 

URL mediaURL = new URL( getDocumentBase(), mediaFile ); 

player = Manager.createRealizedPlayer( mediaURL ); 

if (player.getVisualComponent() != null) 

add("Center", player.getVisualComponent()); 

if (player.getControlPanelComponent() != null) 

add("South", player.getControlPanelComponent()); 

} 

catch (Exception e) { 

System.err.println( "Got exception " + e ); 

} 

} 

public void start() { 

player.start(); 

} 

  

public void stop() { 

player.stop(); 

player.deallocate(); 

} 

public void destroy() { 

player.close(); 

} 

}