Fix out-of-order check after move to 64-bit extended sequence number. (#2004)

Also, clean up the RTCP RR handling a bit by removing redundant check.

pkg/sfu/buffer/rtpstats.go

@@ -560,7 +560,7 @@ func (r *RTPStats) UpdateFromReceiverReport(rr rtcp.ReceptionReport) (rtt uint32
 	r.lock.Lock()
 	defer r.lock.Unlock()
 
-	if !r.initialized || !r.endTime.IsZero() || !r.params.IsReceiverReportDriven || uint64(rr.LastSequenceNumber) < r.sequenceNumber.GetExtendedHighest() {
+	if !r.initialized || !r.endTime.IsZero() || !r.params.IsReceiverReportDriven {
 		// it is possible that the `LastSequenceNumber` in the receiver report is before the starting
 		// sequence number when dummy packets are used to trigger Pion's OnTrack path.
 		return
@@ -575,6 +575,8 @@ func (r *RTPStats) UpdateFromReceiverReport(rr rtcp.ReceptionReport) (rtt uint32
 	if extHighestSNOverridden < r.sequenceNumber.GetExtendedHighest() {
 		// it is possible that the `LastSequenceNumber` in the receiver report is before the starting
 		// sequence number when dummy packets are used to trigger Pion's OnTrack path.
+		r.lastRRTime = time.Now()
+		r.lastRR = rr
 		return
 	}
 

pkg/sfu/rtpmunger.go

@@ -138,8 +138,16 @@ func (r *RTPMunger) PacketDropped(extPkt *buffer.ExtPacket) {
 }
 
 func (r *RTPMunger) UpdateAndGetSnTs(extPkt *buffer.ExtPacket) (*TranslationParamsRTP, error) {
-	diff := extPkt.ExtSequenceNumber - r.extHighestIncomingSN
-	if diff > (1 << 31) {
+	diff := int64(extPkt.ExtSequenceNumber - r.extHighestIncomingSN)
+
+	// can get duplicate packet due to FEC
+	if diff == 0 {
+		return &TranslationParamsRTP{
+			snOrdering: SequenceNumberOrderingDuplicate,
+		}, ErrDuplicatePacket
+	}
+
+	if diff < 0 {
 		// out-of-order, look up sequence number offset cache
 		snOffset, err := r.snRangeMap.GetValue(extPkt.ExtSequenceNumber)
 		if err != nil {
@@ -155,13 +163,6 @@ func (r *RTPMunger) UpdateAndGetSnTs(extPkt *buffer.ExtPacket) (*TranslationPara
 		}, nil
 	}
 
-	// can get duplicate packet due to FEC
-	if diff == 0 {
-		return &TranslationParamsRTP{
-			snOrdering: SequenceNumberOrderingDuplicate,
-		}, ErrDuplicatePacket
-	}
-
 	ordering := SequenceNumberOrderingContiguous
 	if diff > 1 {
 		ordering = SequenceNumberOrderingGap