Run quality scorer when there are no streams. (#1633)

* Run quality scorer when there are no streams.

In the down stream direction, receiver report is used for scoring.
If there are no receiver reports, it should go to `dry` state and report
poor quality.

Update scorer on dry condition only when update score has not happened
for longer than some multiple of update interval. Cannot update on every
interval when there are no streams as receiver report might be just
missed. Waiting for longer to ensure that report is definitely not
received.

* update last stats time

pkg/sfu/connectionquality/connectionstats.go

@@ -15,8 +15,9 @@ import (
 )
 
 const (
-	UpdateInterval   = 5 * time.Second
-	processThreshold = 0.95
+	UpdateInterval           = 5 * time.Second
+	processThreshold         = 0.95
+	noStatsTooLongMultiplier = 2
 )
 
 type ConnectionStatsParams struct {
@@ -158,6 +159,17 @@ func (cs *ConnectionStats) updateLastStatsAt(at time.Time) {
 	cs.lastStatsAt = at
 }
 
+func (cs *ConnectionStats) isTooLongSinceLastStats() bool {
+	cs.lock.Lock()
+	defer cs.lock.Unlock()
+
+	interval := cs.params.UpdateInterval
+	if interval == 0 {
+		interval = UpdateInterval
+	}
+	return !cs.lastStatsAt.IsZero() && time.Since(cs.lastStatsAt) > interval*noStatsTooLongMultiplier
+}
+
 func (cs *ConnectionStats) clearInProcess() {
 	cs.lock.Lock()
 	defer cs.lock.Unlock()
@@ -177,6 +189,10 @@ func (cs *ConnectionStats) getStat(at time.Time) {
 
 	streams := cs.params.GetDeltaStats()
 	if len(streams) == 0 {
+		if cs.isTooLongSinceLastStats() {
+			cs.updateLastStatsAt(at)
+			cs.updateScore(streams, at)
+		}
 		cs.clearInProcess()
 		return
 	}

pkg/sfu/connectionquality/scorer.go

@@ -363,6 +363,10 @@ func (q *qualityScorer) getPacketLossWeight(stat *windowStat) float64 {
 		q.maxPPS = pps
 	}
 
+	if q.maxPPS == 0 {
+		return q.params.PacketLossWeight
+	}
+
 	return math.Sqrt(pps/q.maxPPS) * q.params.PacketLossWeight
 }