Add WriteRTP and Accumulate methods to downTrack.

client.go

@@ -492,14 +492,14 @@ func writeLoop(conn *upConnection, track *upTrack, ch <-chan packetIndex) {
 			}
 
 			for _, l := range local {
-				err := l.track.WriteRTP(&packet)
+				err := l.WriteRTP(&packet)
 				if err != nil {
 					if err != io.ErrClosedPipe {
 						log.Printf("WriteRTP: %v", err)
 					}
 					continue
 				}
-				l.rate.Add(uint32(bytes))
+				l.Accumulate(uint32(bytes))
 			}
 		}
 	}

conn.go

@@ -14,6 +14,7 @@ import (
 	"sfu/jitter"
 	"sfu/packetcache"
 
+	"github.com/pion/rtp"
 	"github.com/pion/webrtc/v2"
 )
 
@@ -247,6 +248,14 @@ type downTrack struct {
 	stats          *receiverStats
 }
 
+func (down *downTrack) WriteRTP(packet *rtp.Packet) error {
+	return down.track.WriteRTP(packet)
+}
+
+func (down *downTrack) Accumulate(bytes uint32) {
+	down.rate.Add(bytes)
+}
+
 func (down *downTrack) GetMaxBitrate(now uint64) uint64 {
 	br1 := down.maxLossBitrate.Get(now)
 	br2 := down.maxREMBBitrate.Get(now)