1 files changed, 57 insertions, 0 deletions
diff --git a/cast/standalone_sender/streaming_video_encoder.cc b/cast/standalone_sender/streaming_video_encoder.cc
new file mode 100644
index 00000000..0e15ab2c
--- /dev/null
+++ b/cast/standalone_sender/streaming_video_encoder.cc
@@ -0,0 +1,57 @@
+// Copyright 2021 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "cast/standalone_sender/streaming_video_encoder.h"
+
+#include "util/chrono_helpers.h"
+
+namespace openscreen {
+namespace cast {
+
+StreamingVideoEncoder::StreamingVideoEncoder(const Parameters& params,
+                                             TaskRunner* task_runner,
+                                             Sender* sender)
+    : params_(params), main_task_runner_(task_runner), sender_(sender) {
+  OSP_DCHECK_LE(1, params_.num_encode_threads);
+  OSP_DCHECK_LE(kMinQuantizer, params_.min_quantizer);
+  OSP_DCHECK_LE(params_.min_quantizer, params_.max_cpu_saver_quantizer);
+  OSP_DCHECK_LE(params_.max_cpu_saver_quantizer, params_.max_quantizer);
+  OSP_DCHECK_LE(params_.max_quantizer, kMaxQuantizer);
+  OSP_DCHECK_LT(0.0, params_.max_time_utilization);
+  OSP_DCHECK_LE(params_.max_time_utilization, 1.0);
+  OSP_DCHECK(main_task_runner_);
+  OSP_DCHECK(sender_);
+}
+
+StreamingVideoEncoder::~StreamingVideoEncoder() {}
+
+void StreamingVideoEncoder::UpdateSpeedSettingForNextFrame(const Stats& stats) {
+  OSP_DCHECK_EQ(std::this_thread::get_id(), encode_thread_.get_id());
+
+  // Combine the speed setting that was used to encode the last frame, and the
+  // quantizer the encoder chose into a single speed metric.
+  const double speed = current_speed_setting_ +
+                       kEquivalentEncodingSpeedStepPerQuantizerStep *
+                           std::max(0, stats.quantizer - params_.min_quantizer);
+
+  // Like |Stats::perfect_quantizer|, this computes a "hindsight" speed setting
+  // for the last frame, one that may have potentially allowed for a
+  // better-quality quantizer choice by the encoder, while also keeping CPU
+  // utilization within budget.
+  const double perfect_speed =
+      speed * stats.time_utilization() / params_.max_time_utilization;
+
+  // Update the ideal speed setting, to be used for the next frame. An
+  // exponentially-decaying weighted average is used here to smooth-out noise.
+  // The weight is based on the duration of the frame that was encoded.
+  constexpr Clock::duration kDecayHalfLife = milliseconds(120);
+  const double ticks = stats.frame_duration.count();
+  const double weight = ticks / (ticks + kDecayHalfLife.count());
+  ideal_speed_setting_ =
+      weight * perfect_speed + (1.0 - weight) * ideal_speed_setting_;
+  OSP_DCHECK(std::isfinite(ideal_speed_setting_));
+}
+
+}  // namespace cast
+}  // namespace openscreen