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 "webrtc/modules/audio_coding/audio_network_adaptor/fec_controller.h"
+
+#include <limits>
+#include <utility>
+
+#include "webrtc/base/checks.h"
+
+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);
+  RTC_DCHECK_LE(fec_enabling_threshold_info_.slope, 0);
+  RTC_DCHECK_LE(
+      GetPacketLossThreshold(config_.fec_enabling_threshold.low_bandwidth_bps,
+                             config_.fec_disabling_threshold,
+                             fec_disabling_threshold_info_),
+      config_.fec_enabling_threshold.low_bandwidth_packet_loss);
+  RTC_DCHECK_LE(
+      GetPacketLossThreshold(config_.fec_enabling_threshold.high_bandwidth_bps,
+                             config_.fec_disabling_threshold,
+                             fec_disabling_threshold_info_),
+      config_.fec_enabling_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);

[michaelt, 2016/09/21 12:51:54]

OPUS uses the packet loss information not only for FEC. OPUS can educing
dependencies among blocks while encoding the input audio, when FEC is off but
packet loss is sent to OPUS.
So it would be good to send packet loss even when FEC is off. 

[minyue-webrtc, 2016/09/21 13:37:52]

Good point!

+  }
+}
+
+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 = bandwidth_diff_bps == 0 ? 0.0 : packet_loss_diff / bandwidth_diff_bps;
+  offset =
+      threshold.low_bandwidth_packet_loss - slope * threshold.low_bandwidth_bps;
+}
+
+float FecController::GetPacketLossThreshold(
+    int bandwidth_bps,
+    const Config::Threshold& threshold,
+    const ThresholdInfo& threshold_info) const {
+  if (bandwidth_bps < threshold.low_bandwidth_bps)
+    return std::numeric_limits<float>::max();
+  if (bandwidth_bps >= threshold.high_bandwidth_bps)
+    return threshold.high_bandwidth_packet_loss;
+  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;
+
+  return *packet_loss >= GetPacketLossThreshold(*metrics.uplink_bandwidth_bps,
+                                                config_.fec_enabling_threshold,
+                                                fec_enabling_threshold_info_);
+}
+
+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;
+
+  return *packet_loss <= GetPacketLossThreshold(*metrics.uplink_bandwidth_bps,
+                                                config_.fec_disabling_threshold,
+                                                fec_disabling_threshold_info_);
+}
+
+}  // namespace webrtc