Do not re-pause a paused track. (#2037)

pkg/sfu/forwarder.go

@@ -811,7 +811,7 @@ func (f *Forwarder) ProvisionalAllocateGetCooperativeTransition(allowOvershoot b
 	if f.provisional.muted || f.provisional.pubMuted {
 		f.provisional.allocatedLayer = buffer.InvalidLayer
 		return VideoTransition{
-			From:           f.vls.GetTarget(),
+			From:           existingTargetLayer,
 			To:             f.provisional.allocatedLayer,
 			BandwidthDelta: -getBandwidthNeeded(f.provisional.Bitrates, existingTargetLayer, f.lastAllocation.BandwidthRequested),
 		}
@@ -1300,12 +1300,18 @@ func (f *Forwarder) Pause(availableLayers []int32, brs Bitrates) VideoAllocation
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
+	existingTargetLayer := f.vls.GetTarget()
+	if !existingTargetLayer.IsValid() {
+		// already paused
+		return f.lastAllocation
+	}
+
 	maxLayer := f.vls.GetMax()
 	maxSeenLayer := f.vls.GetMaxSeen()
 	optimalBandwidthNeeded := getOptimalBandwidthNeeded(f.muted, f.pubMuted, maxSeenLayer.Spatial, brs, maxLayer)
 	alloc := VideoAllocation{
 		BandwidthRequested:  0,
-		BandwidthDelta:      0 - getBandwidthNeeded(brs, f.vls.GetTarget(), f.lastAllocation.BandwidthRequested),
+		BandwidthDelta:      0 - getBandwidthNeeded(brs, existingTargetLayer, f.lastAllocation.BandwidthRequested),
 		Bitrates:            brs,
 		BandwidthNeeded:     optimalBandwidthNeeded,
 		TargetLayer:         buffer.InvalidLayer,

pkg/sfu/streamallocator/streamallocator.go

@@ -883,8 +883,8 @@ func (s *StreamAllocator) allocateTrack(track *Track) {
 		return
 	}
 
-	// already streaming at some layer and transition is not requesting any change, i. e. BandwidthDelta == 0
-	if transition.From.IsValid() && transition.BandwidthDelta == 0 {
+	// a no-op transition
+	if transition.From == transition.To {
 		return
 	}