How to use ob_start() in PHP project while using of Front Controller pattern

class MainApp
{
  static void Main()
  {
    var m = new ConcreteMediator();

    var c1 = new ConcreteColleague1(m);
    var c2 = new ConcreteColleague2(m);

    m.Colleague1 = c1;
    m.Colleague2 = c2;

    c1.Send("How are you?");
    c2.Send("Fine, thanks");

    // Wait for user 
    Console.Read();
  }
}

public class FrontController
{
   public Response HandleRequest(Request request)
   {
       try
       {
         EnsureRequestIsValid(Request request);
         var controller = FindController(request);
         return controller.HandleRequest(request);
       }
       catch (Exception ex)
       {
         return new ErrorResponse(ex); // Exceptions become error pages!
       }
   }

   private MVCController FindController(Request request)
   {
      // some logic here to choose and create the right MVC controller...
      // in reality typically the current application introspects here to find
      // the right controller and method, but you get my point...

      if (Request.Path.StartsWith("/foo/"))
      {
         return new FooController();
      }
   }

   private void EnsureRequestIsValid(Request request)
   {
      // the logic here is always executed, it should throw on error
   }
}