Fix precision error in stats interceptor

When calculating dlrr, precision is lost in integer operations,
errors occur in rtt calculations.
Use float64 just like calculate dlsr just works

Author: Rayleigh Li

pkg/stats/stats_recorder.go

@@ -223,7 +223,7 @@ func (r *recorder) recordIncomingXR(latestStats internalStats, pkt *rtcp.Extende
 					for i := min(r.maxLastReceiverReferenceTimes, len(latestStats.lastReceiverReferenceTimes)) - 1; i >= 0; i-- {
 						lastRR := latestStats.lastReceiverReferenceTimes[i]
 						if (lastRR&0x0000FFFFFFFF0000)>>16 == uint64(xrReport.LastRR) {
-							dlrr := time.Duration(xrReport.DLRR/65536.0) * time.Second
+							dlrr := time.Duration(float64(xrReport.DLRR) / 65536.0 * float64(time.Second))
 							latestStats.RemoteOutboundRTPStreamStats.RoundTripTime = (ts.Add(-dlrr)).Sub(ntp.ToTime(lastRR))
 							latestStats.RemoteOutboundRTPStreamStats.TotalRoundTripTime += latestStats.RemoteOutboundRTPStreamStats.RoundTripTime
 							latestStats.RemoteOutboundRTPStreamStats.RoundTripTimeMeasurements++

pkg/stats/stats_recorder_test.go

@@ -289,3 +289,27 @@ func TestStatsRecorder(t *testing.T) {
 		})
 	}
 }
+
+func TestStatsRecorder_DLRR_Precision(t *testing.T) {
+	r := newRecorder(0, 90_000)
+
+	report := &rtcp.ExtendedReport{
+		Reports: []rtcp.ReportBlock{
+			&rtcp.DLRRReportBlock{
+				Reports: []rtcp.DLRRReport{
+					{
+						SSRC:   5000,
+						LastRR: 762,
+						DLRR:   30000,
+					},
+				},
+			},
+		},
+	}
+
+	s := r.recordIncomingXR(internalStats{
+		lastReceiverReferenceTimes: []uint64{50000000},
+	}, report, time.Time{})
+
+	assert.Equal(t, int64(s.RemoteOutboundRTPStreamStats.RoundTripTime), int64(-9223372036854775808))
+}