From ff08b857003c98b7645319903147782d271d97c2 Mon Sep 17 00:00:00 2001
From: Alessandro Ros <aler9.dev@gmail.com>
Date: Sat, 28 Jun 2025 16:56:44 +0200
Subject: [PATCH] server: add ServerStreamStatsFormat.LocalSSRC (#804)

---
 client_record_test.go   |  2 +-
 server_play_test.go     | 17 ++++++++++++++++-
 server_session.go       | 11 ++++++++---
 server_stream.go        | 27 ++++++---------------------
 server_stream_format.go |  9 +++++++++
 server_stream_stats.go  |  2 ++
 6 files changed, 42 insertions(+), 26 deletions(-)

diff --git a/client_record_test.go b/client_record_test.go
index 24e9023d..99566d31 100644
--- a/client_record_test.go
+++ b/client_record_test.go
@@ -46,7 +46,7 @@ var testRTPPacket = rtp.Packet{
 		CSRC:        []uint32{},
 		SSRC:        0x38F27A2F,
 	},
-	Payload: []byte{1, 2, 3, 4},
+	Payload: []byte{5, 2, 3, 4},
 }
 
 var testRTPPacketMarshaled = mustMarshalPacketRTP(&testRTPPacket)
diff --git a/server_play_test.go b/server_play_test.go
index a744ce97..cde7e573 100644
--- a/server_play_test.go
+++ b/server_play_test.go
@@ -2427,7 +2427,22 @@ func TestServerPlayStreamStats(t *testing.T) {
 	require.NoError(t, err)
 
 	st := stream.Stats()
-	require.Equal(t, uint64(16*2), st.BytesSent)
+	require.Equal(t, &ServerStreamStats{
+		BytesSent:      32,
+		RTPPacketsSent: 2,
+		Medias: map[*description.Media]ServerStreamStatsMedia{
+			stream.Description().Medias[0]: {
+				BytesSent:       32,
+				RTCPPacketsSent: 0,
+				Formats: map[format.Format]ServerStreamStatsFormat{
+					stream.Description().Medias[0].Formats[0]: {
+						RTPPacketsSent: 2,
+						LocalSSRC:      955415087,
+					},
+				},
+			},
+		},
+	}, st)
 }
 
 func TestServerPlayBackChannel(t *testing.T) {
diff --git a/server_session.go b/server_session.go
index df0ab599..877664e1 100644
--- a/server_session.go
+++ b/server_session.go
@@ -1085,9 +1085,14 @@ func (ss *ServerSession) handleRequestInner(sc *ServerConn, req *base.Request) (
 					panic("stream cannot be different than the one returned in previous OnSetup call")
 				}
 
-				ssrc, ok := stream.localSSRC(medi)
-				if ok {
-					th.SSRC = &ssrc
+				// Fill SSRC if there is a single SSRC only
+				// since the Transport header does not support multiple SSRCs.
+				if len(stream.medias[medi].formats) == 1 {
+					format := stream.medias[medi].formats[medi.Formats[0].PayloadType()]
+					ssrc, ok := format.localSSRC()
+					if ok {
+						th.SSRC = &ssrc
+					}
 				}
 			}
 
diff --git a/server_stream.go b/server_stream.go
index 574d112d..a5b58786 100644
--- a/server_stream.go
+++ b/server_stream.go
@@ -152,6 +152,12 @@ func (st *ServerStream) Stats() *ServerStreamStats {
 						for _, fo := range sm.formats {
 							ret[fo.format] = ServerStreamStatsFormat{
 								RTPPacketsSent: atomic.LoadUint64(fo.rtpPacketsSent),
+								LocalSSRC: func() uint32 {
+									if v, ok := fo.localSSRC(); ok {
+										return v
+									}
+									return 0
+								}(),
 							}
 						}
 
@@ -165,27 +171,6 @@ func (st *ServerStream) Stats() *ServerStreamStats {
 	}
 }
 
-func (st *ServerStream) localSSRC(medi *description.Media) (uint32, bool) {
-	st.mutex.Lock()
-	defer st.mutex.Unlock()
-
-	sm := st.medias[medi]
-
-	// localSSRC() is used to fill SSRC inside the Transport header.
-	// if there are multiple formats inside a single media stream,
-	// do not return anything, since Transport headers don't support multiple SSRCs.
-	if len(sm.formats) > 1 {
-		return 0, false
-	}
-
-	stats := firstFormat(sm.formats).rtcpSender.Stats()
-	if stats == nil {
-		return 0, false
-	}
-
-	return stats.LocalSSRC, true
-}
-
 func (st *ServerStream) rtpInfoEntry(medi *description.Media, now time.Time) *headers.RTPInfoEntry {
 	st.mutex.Lock()
 	defer st.mutex.Unlock()
diff --git a/server_stream_format.go b/server_stream_format.go
index 0498ae50..8e7bb653 100644
--- a/server_stream_format.go
+++ b/server_stream_format.go
@@ -35,6 +35,15 @@ func (sf *serverStreamFormat) initialize() {
 	sf.rtcpSender.Initialize()
 }
 
+func (sf *serverStreamFormat) localSSRC() (uint32, bool) {
+	stats := sf.rtcpSender.Stats()
+	if stats != nil {
+		return stats.LocalSSRC, true
+	}
+
+	return 0, false
+}
+
 func (sf *serverStreamFormat) writePacketRTP(byts []byte, pkt *rtp.Packet, ntp time.Time) error {
 	sf.rtcpSender.ProcessPacket(pkt, ntp, sf.format.PTSEqualsDTS(pkt))
 
diff --git a/server_stream_stats.go b/server_stream_stats.go
index 6e845a6e..e83a1ecf 100644
--- a/server_stream_stats.go
+++ b/server_stream_stats.go
@@ -9,6 +9,8 @@ import (
 type ServerStreamStatsFormat struct {
 	// number of sent RTP packets
 	RTPPacketsSent uint64
+	// local SSRC
+	LocalSSRC uint32
 }
 
 // ServerStreamStatsMedia are stream media statistics.