Adding FecController to audio network adaptor.

webrtc/modules/audio_coding/audio_network_adaptor/fec_controller.cc

+/*
+ *  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.
+ */
+
+#include <utility>
+
+#include "webrtc/base/checks.h"
+#include "webrtc/modules/audio_coding/audio_network_adaptor/fec_controller.h"

[hlundin-webrtc, 2016/09/19 14:46:43]

fec_controller.h first of all.

[minyue-webrtc, 2016/09/20 11:58:43]

Done.

+
+namespace webrtc {
+
+FecController::Config::Threshold::Threshold(int low_bandwidth_bps,
+                                            float low_bandwidth_packet_loss,
+                                            int high_bandwidth_bps,
+                                            float high_bandwidth_packet_loss)
+    : low_bandwidth_bps(low_bandwidth_bps),
+      low_bandwidth_packet_loss(low_bandwidth_packet_loss),
+      high_bandwidth_bps(high_bandwidth_bps),
+      high_bandwidth_packet_loss(high_bandwidth_packet_loss) {}
+
+FecController::Config::Config(bool initial_fec_enabled,
+                              const Threshold& fec_enabling_threshold,
+                              const Threshold& fec_disabling_threshold,
+                              int time_constant_ms,
+                              Clock* clock)
+    : initial_fec_enabled(initial_fec_enabled),
+      fec_enabling_threshold(fec_enabling_threshold),
+      fec_disabling_threshold(fec_disabling_threshold),
+      time_constant_ms(time_constant_ms),
+      clock(clock) {}
+
+FecController::FecController(const Config& config)
+    : config_(config),
+      fec_enabled_(config.initial_fec_enabled),
+      packet_loss_smoothed_(
+          new SmoothingFilterImpl(config_.time_constant_ms, config_.clock)),
+      fec_enabling_threshold_info(config_.fec_enabling_threshold),
+      fec_disabling_threshold_info(config_.fec_disabling_threshold) {
+  RTC_DCHECK_LE(fec_enabling_threshold_info.slope, 0);

[hlundin-webrtc, 2016/09/19 14:46:43]

Are these checks enough to make sure the lines don't intersect?

[minyue-webrtc, 2016/09/20 11:58:43]

No, this cannot guarantee no-intersection. they only checks the vertical and
horizontal parts of the curve. Let me try to add intersection detection.

+  RTC_DCHECK_LE(fec_enabling_threshold_info.slope, 0);
+  RTC_DCHECK_GE(config_.fec_enabling_threshold.low_bandwidth_bps,
+                config_.fec_disabling_threshold.low_bandwidth_bps);
+  RTC_DCHECK_GE(config_.fec_enabling_threshold.high_bandwidth_packet_loss,
+                config_.fec_disabling_threshold.high_bandwidth_packet_loss);
+}
+
+FecController::FecController(const Config& config,
+                             std::unique_ptr<SmoothingFilter> smoothing_filter)
+    : FecController(config) {
+  packet_loss_smoothed_ = std::move(smoothing_filter);
+}
+
+FecController::~FecController() = default;
+
+void FecController::MakeDecision(
+    const NetworkMetrics& metrics,
+    AudioNetworkAdaptor::EncoderRuntimeConfig* config) {
+  RTC_DCHECK(!config->enable_fec);
+  RTC_DCHECK(!config->uplink_packet_loss_fraction);
+
+  if (metrics.uplink_packet_loss_fraction)
+    packet_loss_smoothed_->AddSample(*metrics.uplink_packet_loss_fraction);
+
+  fec_enabled_ = fec_enabled_ ? !FecDisablingDecision(metrics)
+                              : FecEnablingDecision(metrics);
+
+  config->enable_fec = rtc::Optional<bool>(fec_enabled_);
+
+  if (fec_enabled_) {
+    auto packet_loss_fraction = packet_loss_smoothed_->GetAverage();
+    config->uplink_packet_loss_fraction = rtc::Optional<float>(
+        packet_loss_fraction ? *packet_loss_fraction : 0.0);
+  } else {
+    config->uplink_packet_loss_fraction = rtc::Optional<float>(0.0);
+  }
+}
+
+FecController::ThresholdInfo::ThresholdInfo(
+    const Config::Threshold& threshold) {
+  int bandwidth_diff_bps =
+      threshold.high_bandwidth_bps - threshold.low_bandwidth_bps;
+  float packet_loss_diff = threshold.high_bandwidth_packet_loss -
+                           threshold.low_bandwidth_packet_loss;
+  slope = packet_loss_diff / bandwidth_diff_bps;

[hlundin-webrtc, 2016/09/19 14:46:43]

How is bandwidth_diff_bps protected from being 0?

[minyue-webrtc, 2016/09/20 11:58:43]

good catch.

+  offset =
+      threshold.low_bandwidth_packet_loss - slope * threshold.low_bandwidth_bps;
+}
+
+float FecController::GetPacketLossThreshold(
+    int bandwidth_bps,
+    const FecController::ThresholdInfo& threshold_info) const {
+  return threshold_info.offset + threshold_info.slope * bandwidth_bps;
+}
+
+bool FecController::FecEnablingDecision(const NetworkMetrics& metrics) const {
+  if (!metrics.uplink_bandwidth_bps)
+    return false;
+
+  auto packet_loss = packet_loss_smoothed_->GetAverage();
+  if (!packet_loss)
+    return false;
+
+  if (*metrics.uplink_bandwidth_bps >=
+          config_.fec_enabling_threshold.high_bandwidth_bps &&
+      *packet_loss >= config_.fec_enabling_threshold.high_bandwidth_packet_loss)
+    return true;
+
+  if (*metrics.uplink_bandwidth_bps <
+          config_.fec_enabling_threshold.high_bandwidth_bps &&
+      *metrics.uplink_bandwidth_bps >=
+          config_.fec_enabling_threshold.low_bandwidth_bps &&
+      *packet_loss >= GetPacketLossThreshold(*metrics.uplink_bandwidth_bps,
+                                             fec_enabling_threshold_info))
+    return true;
+
+  return false;
+}
+
+bool FecController::FecDisablingDecision(const NetworkMetrics& metrics) const {
+  if (!metrics.uplink_bandwidth_bps)
+    return false;
+
+  auto packet_loss = packet_loss_smoothed_->GetAverage();
+  if (!packet_loss)
+    return false;
+
+  if (*metrics.uplink_bandwidth_bps <=
+      config_.fec_disabling_threshold.low_bandwidth_bps)
+    return true;
+
+  if (*metrics.uplink_bandwidth_bps >=
+          config_.fec_disabling_threshold.high_bandwidth_bps &&
+      *packet_loss <=
+          config_.fec_disabling_threshold.high_bandwidth_packet_loss)
+    return true;
+
+  if (*metrics.uplink_bandwidth_bps >
+          config_.fec_disabling_threshold.low_bandwidth_bps &&
+      *metrics.uplink_bandwidth_bps <
+          config_.fec_disabling_threshold.high_bandwidth_bps &&
+      *packet_loss <= GetPacketLossThreshold(*metrics.uplink_bandwidth_bps,
+                                             fec_disabling_threshold_info))
+    return true;
+
+  return false;
+}
+
+}  // namespace webrtc