complete the comments of RTMP protocol.

@@ -1329,12 +1329,76 @@ protected:
 enum SrcPCUCEventType
 {
     // generally, 4bytes event-data
+    
+    /**
+    * The server sends this event to notify the client
+    * that a stream has become functional and can be
+    * used for communication. By default, this event
+    * is sent on ID 0 after the application connect
+    * command is successfully received from the
+    * client. The event data is 4-byte and represents
+    * the stream ID of the stream that became
+    * functional.
+    */
     SrcPCUCStreamBegin              = 0x00,
+
+    /**
+    * The server sends this event to notify the client
+    * that the playback of data is over as requested
+    * on this stream. No more data is sent without
+    * issuing additional commands. The client discards
+    * the messages received for the stream. The
+    * 4 bytes of event data represent the ID of the
+    * stream on which playback has ended.
+    */
     SrcPCUCStreamEOF                = 0x01,
+
+    /**
+    * The server sends this event to notify the client
+    * that there is no more data on the stream. If the
+    * server does not detect any message for a time
+    * period, it can notify the subscribed clients 
+    * that the stream is dry. The 4 bytes of event 
+    * data represent the stream ID of the dry stream. 
+    */
     SrcPCUCStreamDry                = 0x02,
+
+    /**
+    * The client sends this event to inform the server
+    * of the buffer size (in milliseconds) that is 
+    * used to buffer any data coming over a stream.
+    * This event is sent before the server starts  
+    * processing the stream. The first 4 bytes of the
+    * event data represent the stream ID and the next
+    * 4 bytes represent the buffer length, in 
+    * milliseconds.
+    */
     SrcPCUCSetBufferLength          = 0x03, // 8bytes event-data
+
+    /**
+    * The server sends this event to notify the client
+    * that the stream is a recorded stream. The
+    * 4 bytes event data represent the stream ID of
+    * the recorded stream.
+    */
     SrcPCUCStreamIsRecorded         = 0x04,
+
+    /**
+    * The server sends this event to test whether the
+    * client is reachable. Event data is a 4-byte
+    * timestamp, representing the local server time
+    * when the server dispatched the command. The
+    * client responds with kMsgPingResponse on
+    * receiving kMsgPingRequest.  
+    */
     SrcPCUCPingRequest              = 0x06,
+
+    /**
+    * The client sends this event to the server in
+    * response to the ping request. The event data is
+    * a 4-byte timestamp, which was received with the
+    * kMsgPingRequest request.
+    */
     SrcPCUCPingResponse             = 0x07,
 };