diff --git a/protocol/rtp/rtp.go b/protocol/rtp/rtp.go
index 81278236..73f6f15b 100644
--- a/protocol/rtp/rtp.go
+++ b/protocol/rtp/rtp.go
@@ -37,8 +37,8 @@ import (
 )
 
 const (
-	rtpVer           = 2
-	defaultHeadSize  = 3 * 4                            // Header size of an rtp packet.
+	rtpVer           = 2                                // Version of RTP that this package is compatible with.
+	defaultHeadSize  = 12                               // Header size of an rtp packet.
 	defPayloadSize   = sendSize                         // Default payload size for the rtp packet.
 	defPktSize       = defaultHeadSize + defPayloadSize // Default packet size is header size + payload size.
 	optionalFieldIdx = 12                               // This is the idx of optional fields including CSRC and extension header in an RTP packet.