Don't count NACK recovery as properly received packets.

client.go

@@ -10,6 +10,7 @@ import (
 	"errors"
 	"io"
 	"log"
+	"math/bits"
 	"os"
 	"strings"
 	"sync"
@@ -701,7 +702,11 @@ func sendREMB(pc *webrtc.PeerConnection, ssrc uint32, bitrate uint64) error {
 }
 
 func (up *upConnection) sendNACK(track *upTrack, first uint16, bitmap uint16) error {
-	return sendNACK(up.pc, track.track.SSRC(), first, bitmap)
+	err := sendNACK(up.pc, track.track.SSRC(), first, bitmap)
+	if err == nil {
+		track.cache.Expect(1 + bits.OnesCount16(bitmap))
+	}
+	return err
 }
 
 func sendNACK(pc *webrtc.PeerConnection, ssrc uint32, first uint16, bitmap uint16) error {

packetcache/packetcache.go

@@ -114,6 +114,15 @@ func (cache *Cache) Store(seqno uint16, buf []byte) uint16 {
 	return cache.first
 }
 
+func (cache *Cache) Expect(n int) {
+	if n <= 0 {
+		return
+	}
+	cache.mu.Lock()
+	defer cache.mu.Unlock()
+	cache.expected += uint32(n)
+}
+
 func (cache *Cache) Get(seqno uint16) []byte {
 	cache.mu.Lock()
 	defer cache.mu.Unlock()