First-order-FEC recoverability calculation

webrtc/voice_engine/transport_feedback_packet_loss_tracker.h

Index: webrtc/voice_engine/transport_feedback_packet_loss_tracker.h
diff --git a/webrtc/voice_engine/transport_feedback_packet_loss_tracker.h b/webrtc/voice_engine/transport_feedback_packet_loss_tracker.h
index 099c20e92feae469c06591eaf578fba10f3d54ce..bf8fcef4664139060b2a96a2485ca0321a0b702c 100644
--- a/webrtc/voice_engine/transport_feedback_packet_loss_tracker.h
+++ b/webrtc/voice_engine/transport_feedback_packet_loss_tracker.h
@@ -26,20 +26,24 @@ 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;
@@ -67,6 +71,7 @@ class TransportFeedbackPacketLossTracker final {
 
   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_|.
@@ -74,8 +79,9 @@ class TransportFeedbackPacketLossTracker final {
 
   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