Add support backchannel for Tapo source

pkg/mpegts/writer.go

@@ -0,0 +1,219 @@
+package mpegts
+
+type Writer struct {
+	b []byte // packets buffer
+	m int    // crc start
+
+	pid        []uint16
+	counter    []byte
+	streamType []byte
+	timestamp  []uint32
+}
+
+func NewWriter() *Writer {
+	return &Writer{}
+}
+
+func (w *Writer) AddPES(pid uint16, streamType byte) {
+	w.pid = append(w.pid, pid)
+	w.streamType = append(w.streamType, streamType)
+	w.counter = append(w.counter, 0)
+	w.timestamp = append(w.timestamp, 0)
+}
+
+func (w *Writer) WriteByte(b byte) {
+	w.b = append(w.b, b)
+}
+
+func (w *Writer) WriteUint16(i uint16) {
+	w.b = append(w.b, byte(i>>8), byte(i))
+}
+
+func (w *Writer) WriteTime(t uint32) {
+	const onlyPTS = 0x20
+	// [>>32 <<3] [>>24 <<2] [>>16 <<2] [>>8 <<1] [<<1]
+	w.b = append(w.b, onlyPTS|byte(t>>29)|1, byte(t>>22), byte(t>>14)|1, byte(t>>7), byte(t<<1)|1)
+}
+
+func (w *Writer) WriteBytes(b []byte) {
+	w.b = append(w.b, b...)
+}
+
+func (w *Writer) MarkChecksum() {
+	w.m = len(w.b)
+}
+
+func (w *Writer) WriteChecksum() {
+	crc := calcCRC32(0xFFFFFFFF, w.b[w.m:])
+	w.b = append(w.b, byte(crc), byte(crc>>8), byte(crc>>16), byte(crc>>24))
+}
+
+func (w *Writer) FinishPacket() {
+	if n := len(w.b) % PacketSize; n != 0 {
+		w.b = append(w.b, make([]byte, PacketSize-n)...)
+	}
+}
+
+func (w *Writer) Bytes() []byte {
+	if len(w.b)%PacketSize != 0 {
+		panic("wrong packet size")
+	}
+	return w.b
+}
+
+func (w *Writer) Reset() {
+	w.b = nil
+}
+
+const isUnitStart = 0x4000
+const flagHasAdaptation = 0x20
+const flagHasPayload = 0x10
+const lenIsProgramTable = 0xB000
+const tableFlags = 0xC1
+const tableHeader = 0xE000
+const tableLength = 0xF000
+
+const patPID = 0
+const patTableID = 0
+const patTableExtID = 1
+
+func (w *Writer) WritePAT() {
+	w.WriteByte(SyncByte)
+	w.WriteUint16(isUnitStart | patPID) // PAT PID
+	w.WriteByte(flagHasPayload)         // flags...
+
+	w.WriteByte(0) // Pointer field
+
+	w.MarkChecksum()
+	w.WriteByte(patTableID)               // Table ID
+	w.WriteUint16(lenIsProgramTable | 13) // Section length
+	w.WriteUint16(patTableExtID)          // Table ID extension
+	w.WriteByte(tableFlags)               // flags...
+	w.WriteByte(0)                        // Section number
+	w.WriteByte(0)                        // Last section number
+
+	w.WriteUint16(1) // Program num (usual 1)
+	w.WriteUint16(tableHeader + pmtPID)
+
+	w.WriteChecksum()
+
+	w.FinishPacket()
+}
+
+const pmtPID = 18
+const pmtTableID = 2
+const pmtTableExtID = 1
+
+func (w *Writer) WritePMT() {
+	w.WriteByte(SyncByte)
+	w.WriteUint16(isUnitStart | pmtPID) // PMT PID
+	w.WriteByte(flagHasPayload)         // flags...
+
+	w.WriteByte(0) // Pointer field
+
+	tableLen := 13 + uint16(len(w.pid))*5
+
+	w.MarkChecksum()
+	w.WriteByte(pmtTableID)                     // Table ID
+	w.WriteUint16(lenIsProgramTable | tableLen) // Section length
+	w.WriteUint16(pmtTableExtID)                // Table ID extension
+	w.WriteByte(tableFlags)                     // flags...
+	w.WriteByte(0)                              // Section number
+	w.WriteByte(0)                              // Last section number
+
+	w.WriteUint16(tableHeader | w.pid[0]) // PID
+	w.WriteUint16(tableLength | 0)        // Info length
+
+	for i, pid := range w.pid {
+		w.WriteByte(w.streamType[i])
+		w.WriteUint16(tableHeader | pid) // PID
+		w.WriteUint16(tableLength | 0)   // Info len
+	}
+
+	w.WriteChecksum()
+
+	w.FinishPacket()
+}
+
+const pesHeaderSize = PacketSize - 18
+
+func (w *Writer) WritePES(pid uint16, streamID byte, payload []byte) {
+	w.WriteByte(SyncByte)
+	w.WriteUint16(isUnitStart | pid)
+
+	// check if payload lower then max first packet size
+	if len(payload) < PacketSize-18 {
+		w.WriteByte(flagHasAdaptation | flagHasPayload)
+
+		// for 183 payload will be zero
+		adSize := PacketSize - 18 - 1 - byte(len(payload))
+		w.WriteByte(adSize)
+		w.WriteBytes(make([]byte, adSize))
+	} else {
+		w.WriteByte(flagHasPayload)
+	}
+
+	w.WriteByte(0)
+	w.WriteByte(0)
+	w.WriteByte(1)
+
+	w.WriteByte(streamID)
+	w.WriteUint16(uint16(8 + len(payload)))
+
+	w.WriteByte(0x80)
+	w.WriteByte(0x80) // only PTS
+	w.WriteByte(5)    // optional size
+
+	switch w.streamType[0] {
+	case StreamTypePCMATapo:
+		w.timestamp[0] += uint32(len(payload) * 45 / 8)
+	}
+
+	w.WriteTime(w.timestamp[0])
+
+	if len(payload) < PacketSize-18 {
+		w.WriteBytes(payload)
+		return
+	}
+
+	w.WriteBytes(payload[:pesHeaderSize])
+
+	payload = payload[pesHeaderSize:]
+	var counter byte
+
+	for {
+		counter++
+
+		if len(payload) > PacketSize-4 {
+			// payload more then maximum size
+			w.WriteByte(SyncByte)
+			w.WriteUint16(pid)
+			w.WriteByte(flagHasPayload | counter&0xF)
+			w.WriteBytes(payload[:PacketSize-4])
+
+			payload = payload[PacketSize-4:]
+		} else if len(payload) == PacketSize-4 {
+			// payload equal maximum size (last packet)
+			w.WriteByte(SyncByte)
+			w.WriteUint16(pid)
+			w.WriteByte(flagHasPayload | counter&0xF)
+			w.WriteBytes(payload)
+
+			break
+		} else {
+			// payload lower than maximum size (last packet)
+			w.WriteByte(SyncByte)
+			w.WriteUint16(pid)
+			w.WriteByte(flagHasAdaptation | flagHasPayload | counter&0xF)
+
+			// for 183 payload will be zero
+			adSize := PacketSize - 4 - 1 - byte(len(payload))
+			w.WriteByte(adSize)
+			w.WriteBytes(make([]byte, adSize))
+
+			w.WriteBytes(payload)
+
+			break
+		}
+	}
+}