diff --git a/trunk/src/core/srs_core_error.hpp b/trunk/src/core/srs_core_error.hpp
index a0d7a470d..082ca0e1e 100755
--- a/trunk/src/core/srs_core_error.hpp
+++ b/trunk/src/core/srs_core_error.hpp
@@ -57,7 +57,9 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 #define ERROR_RTMP_REQ_CONNECT			305
 #define ERROR_RTMP_REQ_TCURL			306
 #define ERROR_RTMP_MESSAGE_DECODE		307
+#define ERROR_RTMP_MESSAGE_ENCODE		308
 
 #define ERROR_SYSTEM_STREAM_INIT		400
+#define ERROR_SYSTEM_PACKET_INVALID		401
 
 #endif
\ No newline at end of file
diff --git a/trunk/src/core/srs_core_protocol.cpp b/trunk/src/core/srs_core_protocol.cpp
index 139c7a520..48c592654 100755
--- a/trunk/src/core/srs_core_protocol.cpp
+++ b/trunk/src/core/srs_core_protocol.cpp
@@ -884,12 +884,17 @@ int SrsMessage::get_perfer_cid()
 	return packet->get_perfer_cid();
 }
 
-void SrsMessage::set_packet(SrsPacket* pkt)
+void SrsMessage::set_packet(SrsPacket* pkt, int stream_id)
 {
 	if (packet) {
 		delete packet;
 	}
+
 	packet = pkt;
+	
+	header.message_type = packet->get_message_type();
+	header.payload_length = packet->get_payload_length();
+	header.stream_id = stream_id;
 }
 
 int SrsMessage::encode_packet()
@@ -900,8 +905,14 @@ int SrsMessage::encode_packet()
 		srs_warn("packet is empty, send out empty message.");
 		return ret;
 	}
+	// realloc the payload.
+	size = 0;
+	if (payload) {
+		delete[] payload;
+		payload = NULL;
+	}
 	
-	return ret;
+	return packet->encode(size, (char*&)payload);
 }
 
 SrsPacket::SrsPacket()
@@ -923,6 +934,66 @@ int SrsPacket::get_perfer_cid()
 	return 0;
 }
 
+int SrsPacket::get_message_type()
+{
+	return 0;
+}
+
+int SrsPacket::get_payload_length()
+{
+	return get_size();
+}
+
+int SrsPacket::encode(int& psize, char*& ppayload)
+{
+	int ret = ERROR_SUCCESS;
+	
+	int size = get_size();
+	char* payload = NULL;
+	
+	SrsStream stream;
+	
+	if (size > 0) {
+		payload = new char[size];
+		
+		if ((ret = stream.initialize(payload, size)) != ERROR_SUCCESS) {
+			srs_error("initialize the stream failed. ret=%d", ret);
+			delete[] payload;
+			return ret;
+		}
+	}
+	
+	if ((ret = encode_packet(&stream)) != ERROR_SUCCESS) {
+		srs_error("encode the packet failed. ret=%d", ret);
+		delete[] payload;
+		return ret;
+	}
+	
+	psize = size;
+	ppayload = payload;
+	srs_verbose("encode the packet success. size=%d", size);
+	
+	return ret;
+}
+
+int SrsPacket::get_size()
+{
+	return 0;
+}
+
+int SrsPacket::encode_packet(SrsStream* stream)
+{
+	int ret = ERROR_SUCCESS;
+	
+	srs_assert(stream != NULL);
+
+	ret = ERROR_SYSTEM_PACKET_INVALID;
+	srs_error("current packet is not support to sendout. "
+		"paket=%s, ret=%d", get_class_name(), ret);
+	
+	return ret;
+}
+
 SrsConnectAppPacket::SrsConnectAppPacket()
 {
 	command_name = RTMP_AMF0_COMMAND_CONNECT;
@@ -1013,3 +1084,31 @@ int SrsSetWindowAckSizePacket::get_perfer_cid()
 	return RTMP_CID_ProtocolControl;
 }
 
+int SrsSetWindowAckSizePacket::get_message_type()
+{
+	return RTMP_MSG_WindowAcknowledgementSize;
+}
+
+int SrsSetWindowAckSizePacket::get_size()
+{
+	return 4;
+}
+
+int SrsSetWindowAckSizePacket::encode_packet(SrsStream* stream)
+{
+	int ret = ERROR_SUCCESS;
+	
+	if (!stream->require(4)) {
+		ret = ERROR_RTMP_MESSAGE_ENCODE;
+		srs_error("encode ack size packet failed. ret=%d", ret);
+		return ret;
+	}
+	
+	stream->write_4bytes(ackowledgement_window_size);
+	
+	srs_verbose("encode ack size packet "
+		"success. ack_size=%d", ackowledgement_window_size);
+	
+	return ret;
+}
+
diff --git a/trunk/src/core/srs_core_protocol.hpp b/trunk/src/core/srs_core_protocol.hpp
index e6c3a4d61..20c4367ad 100755
--- a/trunk/src/core/srs_core_protocol.hpp
+++ b/trunk/src/core/srs_core_protocol.hpp
@@ -46,6 +46,9 @@ class SrsMessage;
 class SrsChunkStream;
 class SrsAmf0Object;
 
+// convert class name to string.
+#define CLASS_NAME_STRING(className) #className
+
 /**
 * max rtmp header size:
 * 	1bytes basic header,
@@ -237,9 +240,10 @@ public:
 	virtual int get_perfer_cid();
 	/**
 	* set the encoded packet to encode_packet() to payload.
+	* @stream_id, the id of stream which is created by createStream.
 	* @remark, user never free the pkt, the message will auto free it.
 	*/
-	virtual void set_packet(SrsPacket* pkt);
+	virtual void set_packet(SrsPacket* pkt, int stream_id = 0);
 	/**
 	* encode the packet to message payload bytes.
 	* @remark there exists empty packet, so maybe the payload is NULL.
@@ -259,6 +263,36 @@ public:
 	virtual int decode(SrsStream* stream);
 public:
 	virtual int get_perfer_cid();
+	virtual int get_payload_length();
+public:
+	/**
+	* subpacket must override to provide the right message type.
+	*/
+	virtual int get_message_type();
+	/**
+	* the subpacket can override this encode,
+	* for example, video and audio will directly set the payload withou memory copy,
+	* other packet which need to serialize/encode to bytes by override the 
+	* get_size and encode_packet.
+	*/
+	virtual int encode(int& size, char*& payload);
+protected:
+	/**
+	* subpacket can override to calc the packet size.
+	*/
+	virtual int get_size();
+	/**
+	* subpacket can override to encode the payload to stream.
+	*/
+	virtual int encode_packet(SrsStream* stream);
+protected:
+	/**
+	* subpacket must override to provide the right class name.
+	*/
+	virtual const char* get_class_name()
+	{
+		return CLASS_NAME_STRING(SrsPacket);
+	}
 };
 
 /**
@@ -279,6 +313,11 @@ public:
 	virtual ~SrsConnectAppPacket();
 public:
 	virtual int decode(SrsStream* stream);
+protected:
+	virtual const char* get_class_name()
+	{
+		return CLASS_NAME_STRING(SrsConnectAppPacket);
+	}
 };
 
 /**
@@ -299,6 +338,16 @@ public:
 	virtual int decode(SrsStream* stream);
 public:
 	virtual int get_perfer_cid();
+public:
+	virtual int get_message_type();
+protected:
+	virtual int get_size();
+	virtual int encode_packet(SrsStream* stream);
+protected:
+	virtual const char* get_class_name()
+	{
+		return CLASS_NAME_STRING(SrsSetWindowAckSizePacket);
+	}
 };
 
 /**
diff --git a/trunk/src/core/srs_core_stream.cpp b/trunk/src/core/srs_core_stream.cpp
index 3b5e1d6af..3ea887638 100755
--- a/trunk/src/core/srs_core_stream.cpp
+++ b/trunk/src/core/srs_core_stream.cpp
@@ -141,3 +141,14 @@ std::string SrsStream::read_string(int len)
 	return value;
 }
 
+void SrsStream::write_4bytes(int32_t value)
+{
+	srs_assert(require(4));
+	
+	pp = (char*)&value;
+	*p++ = pp[3];
+	*p++ = pp[2];
+	*p++ = pp[1];
+	*p++ = pp[0];
+}
+
diff --git a/trunk/src/core/srs_core_stream.hpp b/trunk/src/core/srs_core_stream.hpp
index 9055492f5..13ee31b55 100755
--- a/trunk/src/core/srs_core_stream.hpp
+++ b/trunk/src/core/srs_core_stream.hpp
@@ -91,6 +91,11 @@ public:
 	* get string from stream, length specifies by param len.
 	*/
 	virtual std::string read_string(int len);
+public:
+	/**
+	* write 4bytes int to stream.
+	*/
+	virtual void write_4bytes(int32_t value);
 };
 
 #endif
\ No newline at end of file