Use the local variable for lastTS. (#750)

Otherwise, the first sample is way off.
Thanks to @milos-lk for the assist and keen 👀

Author: boks1971

pkg/synchronizer/track.go

@@ -207,13 +207,14 @@ func (t *TrackSynchronizer) getPTSWithoutRebase(pkt jitter.ExtPacket) (time.Dura
 		lastTS = ts
 	}
 
-	pts := t.lastPTS + t.toDuration(ts-t.lastTS)
+	pts := t.lastPTS + t.toDuration(ts-lastTS)
 	estimatedPTS := time.Since(t.startTime)
 	if pts < t.lastPTS || !t.acceptable(pts-estimatedPTS) {
 		newStartRTP := ts - t.toRTP(estimatedPTS)
 		t.logger.Infow(
 			"correcting PTS",
 			"currentTS", ts,
+			"lastTS", lastTS,
 			"PTS", pts,
 			"estimatedPTS", estimatedPTS,
 			"offset", pts-estimatedPTS,
@@ -320,13 +321,14 @@ func (t *TrackSynchronizer) getPTSWithRebase(pkt jitter.ExtPacket) (time.Duratio
 		lastTS = ts
 	}
 
-	pts := t.lastPTS + t.toDuration(ts-t.lastTS)
+	pts := t.lastPTS + t.toDuration(ts-lastTS)
 	now := mono.Now()
 	estimatedPTS := now.Sub(t.startTime)
 	if pts < t.lastPTS || !t.acceptable(pts-estimatedPTS) {
 		t.logger.Infow(
 			"correcting PTS",
 			"currentTS", ts,
+			"lastTS", lastTS,
 			"PTS", pts,
 			"estimatedPTS", estimatedPTS,
 			"offset", pts-estimatedPTS,