Bitrate controller for VideoToolbox encoder.

webrtc/modules/video_coding/bitrate_adjuster.cc

+/*
+ *  Copyright 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/video_coding/include/bitrate_adjuster.h"
+
+#include <cmath>
+
+#include "webrtc/base/checks.h"
+#include "webrtc/base/logging.h"
+#include "webrtc/system_wrappers/include/clock.h"
+
+namespace webrtc {
+
+// Update bitrate at most once every second.
+const uint32_t BitrateAdjuster::kBitrateUpdateIntervalMs = 1000;
+
+// Update bitrate at most once every 30 frames.
+const uint32_t BitrateAdjuster::kBitrateUpdateFrameInterval = 30;
+
+// 10 percent of original.
+const float BitrateAdjuster::kBitrateTolerancePct = .1f;
+
+const float BitrateAdjuster::kBytesPerMsToBitsPerSecond = 8 * 1000;
+
+BitrateAdjuster::BitrateAdjuster(Clock* clock,
+                                 float min_adjusted_bitrate_pct,
+                                 float max_adjusted_bitrate_pct)
+    : clock_(clock),
+      min_adjusted_bitrate_pct_(min_adjusted_bitrate_pct),
+      max_adjusted_bitrate_pct_(max_adjusted_bitrate_pct),
+      bitrate_tracker_(1.5 * kBitrateUpdateIntervalMs,
+                       kBytesPerMsToBitsPerSecond) {
+  Reset();
+}
+
+void BitrateAdjuster::SetTargetBitrateBps(uint32_t bitrate_bps) {
+  rtc::CritScope cs(&crit_);
+  // If the change in target bitrate is large, update the adjusted bitrate
+  // immediately since it's likely we have gained or lost a sizeable amount of
+  // bandwidth and we'll want to respond quickly.
+  // If the change in target bitrate fits within the existing tolerance of
+  // encoder output, wait for the next adjustment time to preserve
+  // existing penalties and not forcibly reset the adjusted bitrate to target.
+  // However, if we received many small deltas within an update time
+  // window and one of them exceeds the tolerance when compared to the last
+  // target we updated against, treat it as a large change in target bitrate.
+  if (!IsWithinTolerance(bitrate_bps, target_bitrate_bps_) ||
+      !IsWithinTolerance(bitrate_bps, last_adjusted_target_bitrate_bps_)) {
+    adjusted_bitrate_bps_ = bitrate_bps;
+    last_adjusted_target_bitrate_bps_ = bitrate_bps;
+  }
+  target_bitrate_bps_ = bitrate_bps;
+}
+
+uint32_t BitrateAdjuster::GetTargetBitrateBps() const {
+  rtc::CritScope cs(&crit_);
+  return target_bitrate_bps_;
+}
+
+uint32_t BitrateAdjuster::GetAdjustedBitrateBps() const {
+  rtc::CritScope cs(&crit_);
+  return adjusted_bitrate_bps_;
+}
+
+uint32_t BitrateAdjuster::GetEstimatedBitrateBps() {
+  rtc::CritScope cs(&crit_);
+  return bitrate_tracker_.Rate(clock_->TimeInMilliseconds());
+}
+
+void BitrateAdjuster::Update(size_t frame_size) {
+  rtc::CritScope cs(&crit_);
+  uint32_t current_time_ms = clock_->TimeInMilliseconds();
+  bitrate_tracker_.Update(frame_size, current_time_ms);
+  UpdateBitrate(current_time_ms);
+}
+
+bool BitrateAdjuster::IsWithinTolerance(uint32_t bitrate_bps,
+                                        uint32_t target_bitrate_bps) {
+  if (target_bitrate_bps == 0) {
+    return false;
+  }
+  float delta = std::abs(static_cast<float>(bitrate_bps) -
+                         static_cast<float>(target_bitrate_bps));
+  float delta_pct = delta / target_bitrate_bps;
+  return delta_pct < kBitrateTolerancePct;
+}
+
+uint32_t BitrateAdjuster::GetMinAdjustedBitrateBps() const {
+  return min_adjusted_bitrate_pct_ * target_bitrate_bps_;
+}
+
+uint32_t BitrateAdjuster::GetMaxAdjustedBitrateBps() const {
+  return max_adjusted_bitrate_pct_ * target_bitrate_bps_;
+}
+
+// Only safe to call this after Update calls have stopped
+void BitrateAdjuster::Reset() {
+  rtc::CritScope cs(&crit_);
+  target_bitrate_bps_ = 0;
+  adjusted_bitrate_bps_ = 0;
+  last_adjusted_target_bitrate_bps_ = 0;
+  last_bitrate_update_time_ms_ = 0;
+  frames_since_last_update_ = 0;
+  bitrate_tracker_.Reset();
+}
+
+void BitrateAdjuster::UpdateBitrate(uint32_t current_time_ms) {
+  uint32_t time_since_last_update_ms =
+      current_time_ms - last_bitrate_update_time_ms_;
+  // Don't attempt to update bitrate unless enough time and frames have passed.
+  ++frames_since_last_update_;
+  if (time_since_last_update_ms < kBitrateUpdateIntervalMs ||
+      frames_since_last_update_ < kBitrateUpdateFrameInterval) {
+    return;
+  }
+  float estimated_bitrate_bps = bitrate_tracker_.Rate(current_time_ms);
+  float target_bitrate_bps = target_bitrate_bps_;
+  float error = target_bitrate_bps - estimated_bitrate_bps;
+
+  // Adjust if we've overshot by any amount or if we've undershot too much.
+  if (estimated_bitrate_bps > target_bitrate_bps ||
+      error > kBitrateTolerancePct * target_bitrate_bps) {
+    // Adjust the bitrate by a fraction of the error.
+    float adjustment = .5 * error;
+    float adjusted_bitrate_bps = target_bitrate_bps + adjustment;
+
+    // Clamp the adjustment.
+    float min_bitrate_bps = GetMinAdjustedBitrateBps();
+    float max_bitrate_bps = GetMaxAdjustedBitrateBps();
+    adjusted_bitrate_bps = std::max(adjusted_bitrate_bps, min_bitrate_bps);
+    adjusted_bitrate_bps = std::min(adjusted_bitrate_bps, max_bitrate_bps);
+
+    // Set the adjustment if it's not already set.
+    float last_adjusted_bitrate_bps = adjusted_bitrate_bps_;
+    if (adjusted_bitrate_bps != last_adjusted_bitrate_bps) {
+      LOG(LS_VERBOSE) << "Adjusting encoder bitrate:"
+                      << "\n  target_bitrate:"
+                      << static_cast<uint32_t>(target_bitrate_bps)
+                      << "\n  estimated_bitrate:"
+                      << static_cast<uint32_t>(estimated_bitrate_bps)
+                      << "\n  last_adjusted_bitrate:"
+                      << static_cast<uint32_t>(last_adjusted_bitrate_bps)
+                      << "\n  adjusted_bitrate:"
+                      << static_cast<uint32_t>(adjusted_bitrate_bps);
+      adjusted_bitrate_bps_ = adjusted_bitrate_bps;
+    }
+  }
+  last_bitrate_update_time_ms_ = current_time_ms;
+  frames_since_last_update_ = 0;
+  last_adjusted_target_bitrate_bps_ = target_bitrate_bps_;
+}
+
+}  // namespace webrtc