Get next higher using bit rate. (#1960)

pkg/sfu/streamallocator/streamallocator.go

@@ -852,24 +852,19 @@ func (s *StreamAllocator) allocateTrack(track *Track) {
 	//
 	//   For both cases, do
 	//     a. Find cooperative transition from track that needs allocation.
-	//     b. If track is currently streaming at minimum, do not do anything.
-	//     c. If track is giving back bits, apply the transition and use bits given
+	//     b. If track is giving back bits, apply the transition and use bits given
 	//        back to boost any deficient track(s).
 	//
 	//   If track needs more bits, i.e. upward transition (may need resume or higher layer subscription),
 	//     a. Try to allocate using existing headroom. This can be tried to get the best
 	//        possible fit for the available headroom.
 	//     b. If there is not enough headroom to allocate anything, ask for best offer from
-	//        other tracks that are currently streaming and try to use it.
+	//        other tracks that are currently streaming and try to use it. This is done only if the
+	//        track needing change is not currently streaming, i. e. it has to be resumed.
 	//
 	track.ProvisionalAllocatePrepare()
 	transition := track.ProvisionalAllocateGetCooperativeTransition(FlagAllowOvershootWhileDeficient)
 
-	// track is currently streaming at minimum
-	if transition.BandwidthDelta == 0 {
-		return
-	}
-
 	// downgrade, giving back bits
 	if transition.From.GreaterThan(transition.To) {
 		allocation := track.ProvisionalAllocateCommit()
@@ -928,6 +923,11 @@ func (s *StreamAllocator) allocateTrack(track *Track) {
 		transition = track.ProvisionalAllocateGetCooperativeTransition(FlagAllowOvershootWhileDeficient) // get transition again to reset above allocation attempt using available headroom
 	}
 
+	// track is currently streaming at minimum
+	if transition.BandwidthDelta == 0 {
+		return
+	}
+
 	// if there is not enough headroom, try to redistribute starting with tracks that are closest to their desired.
 	bandwidthAcquired := int64(0)
 	var contributingTracks []*Track