First-order-FEC recoverability calculation

webrtc/voice_engine/transport_feedback_packet_loss_tracker.h

 /*
  *  Copyright (c) 2016 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_VOICE_ENGINE_TRANSPORT_FEEDBACK_PACKET_LOSS_TRACKER_H_
 #define WEBRTC_VOICE_ENGINE_TRANSPORT_FEEDBACK_PACKET_LOSS_TRACKER_H_
 
 #include <map>
 
 #include "webrtc/base/optional.h"
 #include "webrtc/modules/include/module_common_types.h"
 
 namespace webrtc {
 
 namespace rtcp {
 class TransportFeedbackInterface;
 }
 
 class TransportFeedbackPacketLossTracker final {
  public:
   // Up to |max_window_size| latest packet statuses wil be used for calculating
   // the packet loss metrics. When less than |min_window_size| samples are
-  // available for making a reliable estimation, GetPacketLossRates() will
-  // return false to indicate packet loss metrics are not ready.
+  // available for making a reliable estimation, neither PLR nor RPLR would
+  // be considered validly computable.
+  // When |min_pairs_num_for_rplr| pairs or more are available, RPLR is reliably
+  // computable. This is independent of PLR being computable.
   TransportFeedbackPacketLossTracker(size_t min_window_size,
-                                     size_t max_window_size);
+                                     size_t max_window_size,
+                                     size_t min_pairs_num_for_rplr);
 
   void OnReceivedTransportFeedback(
       const rtcp::TransportFeedbackInterface& feedback);
 
-  // Returns true if packet loss rate and packet loss episode duration are ready
-  // and assigns respective values to |*packet_loss_rate| and
-  // |*consecutive_packet_loss_rate|. Continuous packet loss rate is defined as
-  // the probability of losing two adjacent packets.
-  bool GetPacketLossRates(float* packet_loss_rate,
-                          float* consecutive_packet_loss_rate) const;
+  // Returns the packet loss rate, if the window has enough data to
+  // reliably compute it.
+  rtc::Optional<float> GetPacketLossRate() const;
+
+  // Returns the first-order-FEC recoverable packet loss rate, if the window
+  // has enough data to reliably compute it.
+  rtc::Optional<float> GetRecoverablePacketLossRate() const;
 
   // Verifies that the internal states are correct. Only used for tests.
   void Validate() const;
 
  private:
   // PacketStatus is a map from sequence number to a boolean. The boolean is
   // true if it is received.
   typedef std::map<uint16_t, bool> PacketStatus;
   typedef PacketStatus::const_iterator PacketStatusIterator;
 
   void Reset();
   // ReferenceSequenceNumber() provides a sequence number that defines the
   // order of packet reception info stored in |packet_status_window_|. In
   // particular, given any sequence number |x|,
   // (2^16 + x - ref_seq_num_) % 2^16 defines its actual position in
   // |packet_status_window_|.
   uint16_t ReferenceSequenceNumber() const;
   bool IsOldSequenceNumber(uint16_t seq_num) const;
   void InsertPacketStatus(uint16_t seq_num, bool received);
   void RemoveOldestPacketStatus();
   void ApplyPacketStatus(PacketStatusIterator it);
   void UndoPacketStatus(PacketStatusIterator it);
   PacketStatusIterator PreviousPacketStatus(PacketStatusIterator it);
   PacketStatusIterator NextPacketStatus(PacketStatusIterator it);
 
   const size_t min_window_size_;
   const size_t max_window_size_;
+  const size_t min_pairs_num_for_rplr_;
 
   PacketStatus packet_status_window_;
   // |ref_packet_status_| points to the oldest item in |packet_status_window_|.
   PacketStatusIterator ref_packet_status_;
 
   size_t num_received_packets_;
   size_t num_lost_packets_;
-  size_t num_consecutive_losses_;
-  size_t num_consecutive_old_reports_;
+  size_t num_known_status_pairs_;
+  size_t num_loss_followed_by_reception_pairs_;
+  size_t num_consecutive_old_reports_;  // TODO(eladalon): Upcoming CL removes.
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_VOICE_ENGINE_TRANSPORT_FEEDBACK_PACKET_LOSS_TRACKER_H_