code: public String[] getTrackUrls() {
  		Track[] tracks = getTracks();
  
  		if (tracks == null || tracks.length == 0) {
  			return null;
  		}
  
  		String[] urls = new String[tracks.length];
  
  		// this variable needs to be set in the portlet environment.
  		String url = getEnvironment().getWServletPath();
  		Map<String, String> parameters = getBaseParameterMap();
  
  		for (int i = 0; i < urls.length; i++) {
  			parameters.put(TRACK_INDEX_REQUEST_PARAM_KEY, String.valueOf(i));
  			urls[i] = WebUtilities.getPath(url, parameters, true);
  		}
  
  		return urls;
  	}
docs: Creates dynamic URLs that the video clips can be loaded from. In fact the URL points to the main application
  servlet, but includes a non-null for the parameter associated with this WComponent (ie, its label). The
  handleRequest method below detects this when the browser requests a file.
  
  @return the urls to load the video files from, or null if there are no clips defined.