send receiver reports only after receiving a sender report

client.go

@@ -465,8 +465,10 @@ func (c *Client) run() {
 					now := time.Now()
 					for trackID, cct := range c.tracks {
 						rr := cct.rtcpReceiver.Report(now)
+						if rr != nil {
 							c.WritePacketRTCP(trackID, rr)
 						}
+					}
 
 					c.udpReportTimer = time.NewTimer(c.udpReceiverReportPeriod)
 				} else { // Record

pkg/rtcpreceiver/rtcpreceiver.go

@@ -52,10 +52,16 @@ func New(receiverSSRC *uint32, clockRate int) *RTCPReceiver {
 }
 
 // Report generates a RTCP receiver report.
+// It returns nil if no RTCP sender reports have been passed to ProcessPacketRTCP yet.
 func (rr *RTCPReceiver) Report(ts time.Time) []byte {
 	rr.mutex.Lock()
 	defer rr.mutex.Unlock()
 
+	var zero time.Time
+	if rr.lastSenderReportTime == zero {
+		return nil
+	}
+
 	report := &rtcp.ReceiverReport{
 		SSRC: rr.receiverSSRC,
 		Reports: []rtcp.ReceptionReport{

pkg/rtcpreceiver/rtcpreceiver_test.go

@@ -13,6 +13,8 @@ func TestRTCPReceiverBase(t *testing.T) {
 	v := uint32(0x65f83afb)
 	rr := New(&v, 90000)
 
+	require.Equal(t, []byte(nil), rr.Report(time.Now()))
+
 	srPkt := rtcp.SenderReport{
 		SSRC:        0xba9da416,
 		NTPTime:     0xe363887a17ced916,

pkg/rtcpsender/rtcpsender_test.go

@@ -12,6 +12,8 @@ import (
 func TestRTCPSender(t *testing.T) {
 	rs := New(90000)
 
+	require.Equal(t, []byte(nil), rs.Report(time.Now()))
+
 	rtpPkt := rtp.Packet{
 		Header: rtp.Header{
 			Version:        2,

server_publish_test.go

@@ -1167,6 +1167,19 @@ func TestServerPublishRTCPReport(t *testing.T) {
 	})
 	require.NoError(t, err)
 
+	byts, _ = (&rtcp.SenderReport{
+		SSRC:        753621,
+		NTPTime:     0xcbddcc34999997ff,
+		RTPTime:     54352,
+		PacketCount: 1,
+		OctetCount:  4,
+	}).Marshal()
+	_, err = l2.WriteTo(byts, &net.UDPAddr{
+		IP:   net.ParseIP("127.0.0.1"),
+		Port: th.ServerPorts[1],
+	})
+	require.NoError(t, err)
+
 	// skip firewall opening
 	buf := make([]byte, 2048)
 	_, _, err = l2.ReadFrom(buf)

serversession.go

@@ -324,8 +324,10 @@ func (ss *ServerSession) run() {
 				now := time.Now()
 
 				for trackID, track := range ss.announcedTracks {
-					r := track.rtcpReceiver.Report(now)
-					ss.WritePacketRTCP(trackID, r)
+					rr := track.rtcpReceiver.Report(now)
+					if rr != nil {
+						ss.WritePacketRTCP(trackID, rr)
+					}
 				}
 
 				ss.udpReceiverReportTimer = time.NewTimer(ss.s.udpReceiverReportPeriod)