Refactor NACK bitrate allocation

webrtc/modules/pacing/paced_sender.h

Index: webrtc/modules/pacing/paced_sender.h
diff --git a/webrtc/modules/pacing/paced_sender.h b/webrtc/modules/pacing/paced_sender.h
index 1d9f2de2614d14567ca1b15d2d8e17e9770d007b..35873be013938a8c007d6a720436fdc33dd99733 100644
--- a/webrtc/modules/pacing/paced_sender.h
+++ b/webrtc/modules/pacing/paced_sender.h
@@ -15,6 +15,7 @@
 #include <memory>
 #include <set>
 
+#include "webrtc/base/rate_statistics.h"
 #include "webrtc/base/thread_annotations.h"
 #include "webrtc/modules/include/module.h"
 #include "webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h"
@@ -108,6 +109,16 @@ class PacedSender : public Module, public RtpPacketSender {
                     size_t bytes,
                     bool retransmission) override;
 
+  // Try to allocate bitrate for sending a retransmission. This may fail if too
+  // much retransmission is requested in relation to payload.
+  bool AllocateRetransmissionBitrate(size_t bytes) override;

[danilchap, 2016/06/23 12:46:12]

this function doesn't seem to allocate(reserve) bitrate(speed), but checks if
retransmission is allowed because of bitrate.
It also assume the packet would be then retransmitted and updates rate because
of it.
May be remove this function from interface, and call it from InsertPacket
instead (that would be allowed to fail now).
i.e. in PacedPacket::InsertPacket 
have code like
if (retransmission) {
  if (!HasBandwidthForRetransmission()) {
    return false;
  }
  retransmission_rate_.Update(bytes, now_ms);
}

[sprang_webrtc, 2016/06/28 09:12:32]

Actually, having this in the pacer didn't work well. I've moved it out to a
separate interface and renamed it RateLimiter.

+
+  // The current retransmission bitrate, in bps.
+  int CurrentRetransmissionBitrate() override;
+
+  // Set the current RTT. Used to determine maximum retransmission bitrate.
+  void OnRttUpdate(int64_t rtt);
+
   // Returns the time since the oldest queued packet was enqueued.
   virtual int64_t QueueInMs() const;
 
@@ -166,6 +177,11 @@ class PacedSender : public Module, public RtpPacketSender {
 
   std::unique_ptr<paced_sender::PacketQueue> packets_ GUARDED_BY(critsect_);
   uint64_t packet_counter_;
+
+  // Average retransmission bitrate, incoming to the pacer. Limits
+  // retransmission bitrate in relation to payload bitrate.
+  RateStatistics retransmission_rate_ GUARDED_BY(critsect_);
+  int64_t rtt_ms_ GUARDED_BY(critsect_);
 };
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_PACING_PACED_SENDER_H_