refine the pithy print mechenism.

trunk/src/app/srs_app_pithy_print.hpp

@@ -56,9 +56,12 @@ public:
 
 /**
  * the stage is used for a collection of object to do print,
-* the print time in a stage is constant and not changed.
+ * the print time in a stage is constant and not changed,
+ * that is, we always got one message to print every specified time.
+ *
  * for example, stage #1 for all play clients, print time is 3s,
-* if there is 10clients, then all clients should print in 10*3s.
+ * if there is 1client, it will print every 3s.
+ * if there is 10clients, random select one to print every 3s.
  * Usage:
          SrsPithyPrint* pprint = SrsPithyPrint::create_rtmp_play();
          SrsAutoFree(SrsPithyPrint, pprint);