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 "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;
+
+// 5 percent of original.
+const uint32_t BitrateAdjuster::kBitrateTolerancePct = 5;
+
+BitrateAdjuster::BitrateAdjuster(Clock* clock)
+    : clock_(clock),
+      bitrate_tracker_(1.5 * kBitrateUpdateIntervalMs, 8) {
+  Reset();
+}
+
+void BitrateAdjuster::SetTargetBitrate(uint32_t bitrate_kbit) {
+  rtc::CritScope cs(&crit_);
+  target_bitrate_kbit_ = bitrate_kbit;
+  // If we haven't had time to determine what adjustment is required yet then
+  // just use the target.
+  adjusted_bitrate_kbit_ = target_bitrate_kbit_;
+}
+
+uint32_t BitrateAdjuster::GetTargetBitrate() const {
+  rtc::CritScope cs(&crit_);
+  return target_bitrate_kbit_;
+}
+
+uint32_t BitrateAdjuster::GetAdjustedBitrate() const {
+  rtc::CritScope cs(&crit_);
+  return adjusted_bitrate_kbit_;
+}
+
+uint32_t BitrateAdjuster::GetEstimatedBitrate() {
+  rtc::CritScope cs(&crit_);
+  return bitrate_tracker_.Rate(clock_->TimeInMilliseconds());
+}
+
+uint32_t BitrateAdjuster::GetMinAdjustedBitrate() const {
+  rtc::CritScope cs(&crit_);
+  // Half of target bitrate.
+  return target_bitrate_kbit_ / 2;
+}
+
+uint32_t BitrateAdjuster::GetMaxAdjustedBitrate() const {
+  rtc::CritScope cs(&crit_);
+  // 95% of target bitrate. In practice we know that the VideoToolbox encoder
+  // on iOS overshoots regularly. Setting it to 95% seems to reduce
+  // oscillations.
+  return .95 * target_bitrate_kbit_;
+}
+
+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);
+}
+
+// Only safe to call this after Update calls have stopped
+void BitrateAdjuster::Reset() {
+  rtc::CritScope cs(&crit_);
+  target_bitrate_kbit_ = 0;

[pbos-webrtc, 2016/02/19 11:26:39]

Can this whole thing operate on bps_ instead?

[tkchin_webrtc, 2016/02/19 23:30:05]

Done.

+  adjusted_bitrate_kbit_ = 0;
+  last_bitrate_update_time_ms_ = 0;
+  frames_since_last_update_ = 0;
+  bitrate_tracker_.Reset();
+}
+
+void BitrateAdjuster::UpdateBitrate(uint32_t current_time_ms) {
+  rtc::CritScope cs(&crit_);
+  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 bitrate = bitrate_tracker_.Rate(current_time_ms);
+  float target_bitrate = target_bitrate_kbit_;
+  float error = target_bitrate - bitrate;
+
+  // Adjust if we've overshot by any amount or if we've undershot too much.
+  if (bitrate > target_bitrate ||
+      error * 100 > kBitrateTolerancePct * target_bitrate) {
+    // Adjust the bitrate by a fraction of the error.
+    float adjustment = .5 * error;
+    float adjusted_bitrate = target_bitrate + adjustment;
+
+    // Clamp the adjustment to [0.5 * target, 0.95 * target].
+    float min_bitrate = GetMinAdjustedBitrate();
+    float max_bitrate = GetMaxAdjustedBitrate();
+    adjusted_bitrate = std::max(adjusted_bitrate, min_bitrate);

[pbos-webrtc, 2016/02/19 11:26:39]

units on all of these (_bps preferred)

[tkchin_webrtc, 2016/02/19 23:30:05]

Done.

+    adjusted_bitrate = std::min(adjusted_bitrate, max_bitrate);
+
+    // Set the adjustment if it's not already set.
+    float last_adjusted_bitrate = adjusted_bitrate_kbit_;
+    if (adjusted_bitrate != last_adjusted_bitrate) {
+      LOG(LS_VERBOSE) << "Adjusting encoder bitrate:"
+                      << "\n  target_bitrate:" << target_bitrate
+                      << "\n  actual_bitrate:" << bitrate
+                      << "\n  last_adjusted_bitrate:"
+                      << static_cast<uint32_t>(last_adjusted_bitrate)
+                      << "\n  adjusted_bitrate:"
+                      << static_cast<uint32_t>(adjusted_bitrate);
+      adjusted_bitrate_kbit_ = adjusted_bitrate;
+    }
+  }
+  last_bitrate_update_time_ms_ = current_time_ms;
+  frames_since_last_update_ = 0;
+}
+
+}  // namespace webrtc