Fetch receive time only once per frame instead of once per packet

src/RtpFecQueue.c

@@ -44,7 +44,6 @@ static int queuePacket(PRTP_FEC_QUEUE queue, PRTPFEC_QUEUE_ENTRY newEntry, int h
     newEntry->packet = packet;
     newEntry->length = length;
     newEntry->isParity = isParity;
-    newEntry->receiveTimeMs = PltGetMillis();
     newEntry->prev = NULL;
     newEntry->next = NULL;
 
@@ -266,6 +265,13 @@ static void submitCompletedFrame(PRTP_FEC_QUEUE queue) {
                 removeEntry(queue, entry);
                 entry->prev = entry->next = NULL;
 
+                // To avoid having to sample the system time for each packet, we cheat
+                // and use the first packet's receive time for all packets. This ends up
+                // actually being better for the measurements that the depacketizer does,
+                // since it properly handles out of order packets.
+                LC_ASSERT(queue->bufferFirstRecvTimeMs != 0);
+                entry->receiveTimeMs = queue->bufferFirstRecvTimeMs;
+
                 // Submit this packet for decoding. It will own freeing the entry now.
                 queueRtpPacket(entry);
                 break;
@@ -331,6 +337,7 @@ int RtpfAddPacket(PRTP_FEC_QUEUE queue, PRTP_PACKET packet, int length, PRTPFEC_
         queue->bufferTail = NULL;
         queue->bufferSize = 0;
         
+        queue->bufferFirstRecvTimeMs = PltGetMillis();
         queue->bufferLowestSequenceNumber = U16(packet->sequenceNumber - fecIndex);
         queue->nextContiguousSequenceNumber = queue->bufferLowestSequenceNumber;
         queue->receivedBufferDataPackets = 0;

src/RtpFecQueue.h

@@ -15,6 +15,7 @@ typedef struct _RTPFEC_QUEUE_ENTRY {
 typedef struct _RTP_FEC_QUEUE {
     PRTPFEC_QUEUE_ENTRY bufferHead;
     PRTPFEC_QUEUE_ENTRY bufferTail;
+    unsigned long long bufferFirstRecvTimeMs;
     int bufferSize;
     int bufferLowestSequenceNumber;
     int bufferHighestSequenceNumber;

src/VideoDepacketizer.c

@@ -669,6 +669,9 @@ void processRtpPayload(PNV_VIDEO_PACKET videoPacket, int length, unsigned long l
 void queueRtpPacket(PRTPFEC_QUEUE_ENTRY queueEntry) {
     int dataOffset;
 
+    LC_ASSERT(!queueEntry->isParity);
+    LC_ASSERT(queueEntry->receiveTimeMs != 0);
+
     dataOffset = sizeof(*queueEntry->packet);
     if (queueEntry->packet->header & FLAG_EXTENSION) {
         dataOffset += 4; // 2 additional fields