rtmp: add Chunk2

internal/rtmp/base/chunk1.go

@@ -11,16 +11,20 @@ import (
 // formats) SHOULD use this format for the first chunk of each new
 // message after the first.
 type Chunk1 struct {
-	ChunkStreamID byte
-	Type          MessageType
-	BodyLen       uint32
-	Body          []byte
+	ChunkStreamID  byte
+	TimestampDelta uint32
+	Type           MessageType
+	BodyLen        uint32
+	Body           []byte
 }
 
 // Write writes the chunk.
 func (c Chunk1) Write(w io.Writer) error {
 	header := make([]byte, 8)
 	header[0] = 1<<6 | c.ChunkStreamID
+	header[1] = byte(c.TimestampDelta >> 16)
+	header[2] = byte(c.TimestampDelta >> 8)
+	header[3] = byte(c.TimestampDelta)
 	header[4] = byte(c.BodyLen >> 16)
 	header[5] = byte(c.BodyLen >> 8)
 	header[6] = byte(c.BodyLen)

internal/rtmp/base/chunk2.go

@@ -0,0 +1,31 @@
+package base
+
+import (
+	"io"
+)
+
+// Chunk2 is a type 2 chunk.
+//  Neither the stream ID nor the
+// message length is included; this chunk has the same stream ID and
+// message length as the preceding chunk.
+type Chunk2 struct {
+	ChunkStreamID  byte
+	TimestampDelta uint32
+	Body           []byte
+}
+
+// Write writes the chunk.
+func (c Chunk2) Write(w io.Writer) error {
+	header := make([]byte, 4)
+	header[0] = 1<<6 | c.ChunkStreamID
+	header[1] = byte(c.TimestampDelta >> 16)
+	header[2] = byte(c.TimestampDelta >> 8)
+	header[3] = byte(c.TimestampDelta)
+	_, err := w.Write(header)
+	if err != nil {
+		return err
+	}
+
+	_, err = w.Write(c.Body)
+	return err
+}

internal/rtmp/base/messagewriter.go

@@ -7,6 +7,10 @@ import (
 type messageWriterChunkStream struct {
 	mw                  *MessageWriter
 	lastMessageStreamID *uint32
+	lastType            *MessageType
+	lastBodyLen         *int
+	lastTimestamp       *uint32
+	lastTimestampDelta  *uint32
 }
 
 func (wc *messageWriterChunkStream) write(msg *Message) error {
@@ -14,6 +18,12 @@ func (wc *messageWriterChunkStream) write(msg *Message) error {
 	pos := 0
 	firstChunk := true
 
+	var timestampDelta *uint32
+	if wc.lastTimestamp != nil {
+		v := msg.Timestamp - *wc.lastTimestamp
+		timestampDelta = &v
+	}
+
 	for {
 		chunkBodyLen := bodyLen - pos
 		if chunkBodyLen > wc.mw.chunkSize {
@@ -23,7 +33,8 @@ func (wc *messageWriterChunkStream) write(msg *Message) error {
 		if firstChunk {
 			firstChunk = false
 
-			if wc.lastMessageStreamID == nil || *wc.lastMessageStreamID != msg.MessageStreamID {
+			switch {
+			case wc.lastMessageStreamID == nil || *wc.lastMessageStreamID != msg.MessageStreamID:
 				err := Chunk0{
 					ChunkStreamID:   msg.ChunkStreamID,
 					Type:            msg.Type,
@@ -35,19 +46,51 @@ func (wc *messageWriterChunkStream) write(msg *Message) error {
 					return err
 				}
 
-				v := msg.MessageStreamID
-				wc.lastMessageStreamID = &v
-			} else {
+			case wc.lastTimestampDelta == nil || *wc.lastType != msg.Type || *wc.lastBodyLen != bodyLen:
 				err := Chunk1{
+					ChunkStreamID:  msg.ChunkStreamID,
+					TimestampDelta: *timestampDelta,
+					Type:           msg.Type,
+					BodyLen:        uint32(bodyLen),
+					Body:           msg.Body[pos : pos+chunkBodyLen],
+				}.Write(wc.mw.w)
+				if err != nil {
+					return err
+				}
+
+			case *wc.lastTimestampDelta != *timestampDelta:
+				err := Chunk2{
+					ChunkStreamID:  msg.ChunkStreamID,
+					TimestampDelta: *timestampDelta,
+					Body:           msg.Body[pos : pos+chunkBodyLen],
+				}.Write(wc.mw.w)
+				if err != nil {
+					return err
+				}
+
+			default:
+				err := Chunk3{
 					ChunkStreamID: msg.ChunkStreamID,
-					Type:          msg.Type,
-					BodyLen:       uint32(bodyLen),
 					Body:          msg.Body[pos : pos+chunkBodyLen],
 				}.Write(wc.mw.w)
 				if err != nil {
 					return err
 				}
 			}
+
+			v1 := msg.MessageStreamID
+			wc.lastMessageStreamID = &v1
+			v2 := msg.Type
+			wc.lastType = &v2
+			v3 := bodyLen
+			wc.lastBodyLen = &v3
+			v4 := msg.Timestamp
+			wc.lastTimestamp = &v4
+
+			if timestampDelta != nil {
+				v5 := *timestampDelta
+				wc.lastTimestampDelta = &v5
+			}
 		} else {
 			err := Chunk3{
 				ChunkStreamID: msg.ChunkStreamID,