Add statistics gathering for packet loss.

webrtc/modules/rtp_rtcp/source/packet_loss_stats.h

Index: webrtc/modules/rtp_rtcp/source/packet_loss_stats.h
diff --git a/webrtc/modules/rtp_rtcp/source/packet_loss_stats.h b/webrtc/modules/rtp_rtcp/source/packet_loss_stats.h
new file mode 100644
index 0000000000000000000000000000000000000000..dc8165bcd77aa0d373ad60edc801d2fbe07f4268
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+++ b/webrtc/modules/rtp_rtcp/source/packet_loss_stats.h
@@ -0,0 +1,57 @@
+/*
+ *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_MODULES_RTP_RTCP_SOURCE_PACKET_LOSS_STATS_H_
+#define WEBRTC_MODULES_RTP_RTCP_SOURCE_PACKET_LOSS_STATS_H_
+
+#include <stdint.h>
+#include <set>
+
+namespace webrtc {
+
+// Keeps track of statistics of packet loss including whether losses are a
+// single packet or multiple packets in a row.
+class PacketLossStats {
+ public:
+  PacketLossStats();
+  ~PacketLossStats() {}
+
+  // Adds a lost packet to the stats by sequence number.
+  void AddLostPacket(uint16_t sequence_number);
+
+  // Query the number of packets that were lost by themselves, no neighboring

[noahric, 2015/06/26 00:21:19]

Queries (for the rest too)

[bcornell, 2015/06/30 19:47:45]

Done.

+  // packets were lost.
+  int GetSingleLossCount() const;
+
+  // Query the number of times that multiple packets with sequential numbers
+  // were lost. This is the number of events with more than one packet lost,
+  // regardless of the size of the event;
+  int GetMultipleLossEventCount() const;
+
+  // Query the number of packets lost in multiple packet loss events. Combined
+  // with the event count, this can be used to determine how large events are.

[noahric, 2015/06/26 00:21:19]

I'd say explicitly "the average event size", if that's what you mean

[bcornell, 2015/06/30 19:47:45]

Done.

+  int GetMultipleLossPacketCount() const;
+
+ private:
+  std::set<uint16_t> lost_packets_buffer_;
+  std::set<uint16_t> lost_packets_wrapped_buffer_;
+  int single_loss_historic_count_;
+  int multiple_loss_historic_event_count_;
+  int multiple_loss_historic_packet_count_;
+
+  void ComputeLossCounts(int* out_single_loss_count,
+                         int* out_multiple_loss_event_count,
+                         int* out_multiple_loss_packet_count) const;
+  void PruneBuffer();
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_PACKET_LOSS_STATS_H_