1 files changed, 268 insertions, 0 deletions
diff --git a/third_party/libwebrtc/modules/video_coding/utility/frame_dropper.cc b/third_party/libwebrtc/modules/video_coding/utility/frame_dropper.cc
new file mode 100644
index 0000000000..8ea8a8e268
--- /dev/null
+++ b/third_party/libwebrtc/modules/video_coding/utility/frame_dropper.cc
@@ -0,0 +1,268 @@
+/*
+ *  Copyright (c) 2011 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 "modules/video_coding/utility/frame_dropper.h"
+
+#include <algorithm>
+
+namespace webrtc {
+
+namespace {
+
+const float kDefaultFrameSizeAlpha = 0.9f;
+const float kDefaultKeyFrameRatioAlpha = 0.99f;
+// 1 key frame every 10th second in 30 fps.
+const float kDefaultKeyFrameRatioValue = 1 / 300.0f;
+
+const float kDefaultDropRatioAlpha = 0.9f;
+const float kDefaultDropRatioValue = 0.96f;
+// Maximum duration over which frames are continuously dropped.
+const float kDefaultMaxDropDurationSecs = 4.0f;
+
+// Default target bitrate.
+// TODO(isheriff): Should this be higher to avoid dropping too many packets when
+// the bandwidth is unknown at the start ?
+const float kDefaultTargetBitrateKbps = 300.0f;
+const float kDefaultIncomingFrameRate = 30;
+const float kLeakyBucketSizeSeconds = 0.5f;
+
+// A delta frame that is bigger than `kLargeDeltaFactor` times the average
+// delta frame is a large frame that is spread out for accumulation.
+const int kLargeDeltaFactor = 3;
+
+// Cap on the frame size accumulator to prevent excessive drops.
+const float kAccumulatorCapBufferSizeSecs = 3.0f;
+}  // namespace
+
+FrameDropper::FrameDropper()
+    : key_frame_ratio_(kDefaultKeyFrameRatioAlpha),
+      delta_frame_size_avg_kbits_(kDefaultFrameSizeAlpha),
+      drop_ratio_(kDefaultDropRatioAlpha, kDefaultDropRatioValue),
+      enabled_(true),
+      max_drop_duration_secs_(kDefaultMaxDropDurationSecs) {
+  Reset();
+}
+
+FrameDropper::~FrameDropper() = default;
+
+void FrameDropper::Reset() {
+  key_frame_ratio_.Reset(kDefaultKeyFrameRatioAlpha);
+  key_frame_ratio_.Apply(1.0f, kDefaultKeyFrameRatioValue);
+  delta_frame_size_avg_kbits_.Reset(kDefaultFrameSizeAlpha);
+
+  accumulator_ = 0.0f;
+  accumulator_max_ = kDefaultTargetBitrateKbps / 2;
+  target_bitrate_ = kDefaultTargetBitrateKbps;
+  incoming_frame_rate_ = kDefaultIncomingFrameRate;
+
+  large_frame_accumulation_count_ = 0;
+  large_frame_accumulation_chunk_size_ = 0;
+  large_frame_accumulation_spread_ = 0.5 * kDefaultIncomingFrameRate;
+
+  drop_next_ = false;
+  drop_ratio_.Reset(0.9f);
+  drop_ratio_.Apply(0.0f, 0.0f);
+  drop_count_ = 0;
+  was_below_max_ = true;
+}
+
+void FrameDropper::Enable(bool enable) {
+  enabled_ = enable;
+}
+
+void FrameDropper::Fill(size_t framesize_bytes, bool delta_frame) {
+  if (!enabled_) {
+    return;
+  }
+  float framesize_kbits = 8.0f * static_cast<float>(framesize_bytes) / 1000.0f;
+  if (!delta_frame) {
+    key_frame_ratio_.Apply(1.0, 1.0);
+    // Do not spread if we are already doing it (or we risk dropping bits that
+    // need accumulation). Given we compute the key frame ratio and spread
+    // based on that, this should not normally happen.
+    if (large_frame_accumulation_count_ == 0) {
+      if (key_frame_ratio_.filtered() > 1e-5 &&
+          1 / key_frame_ratio_.filtered() < large_frame_accumulation_spread_) {
+        large_frame_accumulation_count_ =
+            static_cast<int32_t>(1 / key_frame_ratio_.filtered() + 0.5);
+      } else {
+        large_frame_accumulation_count_ =
+            static_cast<int32_t>(large_frame_accumulation_spread_ + 0.5);
+      }
+      large_frame_accumulation_chunk_size_ =
+          framesize_kbits / large_frame_accumulation_count_;
+      framesize_kbits = 0;
+    }
+  } else {
+    // Identify if it is an unusually large delta frame and spread accumulation
+    // if that is the case.
+    if (delta_frame_size_avg_kbits_.filtered() != -1 &&
+        (framesize_kbits >
+         kLargeDeltaFactor * delta_frame_size_avg_kbits_.filtered()) &&
+        large_frame_accumulation_count_ == 0) {
+      large_frame_accumulation_count_ =
+          static_cast<int32_t>(large_frame_accumulation_spread_ + 0.5);
+      large_frame_accumulation_chunk_size_ =
+          framesize_kbits / large_frame_accumulation_count_;
+      framesize_kbits = 0;
+    } else {
+      delta_frame_size_avg_kbits_.Apply(1, framesize_kbits);
+    }
+    key_frame_ratio_.Apply(1.0, 0.0);
+  }
+  // Change the level of the accumulator (bucket)
+  accumulator_ += framesize_kbits;
+  CapAccumulator();
+}
+
+void FrameDropper::Leak(uint32_t input_framerate) {
+  if (!enabled_) {
+    return;
+  }
+  if (input_framerate < 1) {
+    return;
+  }
+  if (target_bitrate_ < 0.0f) {
+    return;
+  }
+  // Add lower bound for large frame accumulation spread.
+  large_frame_accumulation_spread_ = std::max(0.5 * input_framerate, 5.0);
+  // Expected bits per frame based on current input frame rate.
+  float expected_bits_per_frame = target_bitrate_ / input_framerate;
+  if (large_frame_accumulation_count_ > 0) {
+    expected_bits_per_frame -= large_frame_accumulation_chunk_size_;
+    --large_frame_accumulation_count_;
+  }
+  accumulator_ -= expected_bits_per_frame;
+  if (accumulator_ < 0.0f) {
+    accumulator_ = 0.0f;
+  }
+  UpdateRatio();
+}
+
+void FrameDropper::UpdateRatio() {
+  if (accumulator_ > 1.3f * accumulator_max_) {
+    // Too far above accumulator max, react faster.
+    drop_ratio_.UpdateBase(0.8f);
+  } else {
+    // Go back to normal reaction.
+    drop_ratio_.UpdateBase(0.9f);
+  }
+  if (accumulator_ > accumulator_max_) {
+    // We are above accumulator max, and should ideally drop a frame. Increase
+    // the drop_ratio_ and drop the frame later.
+    if (was_below_max_) {
+      drop_next_ = true;
+    }
+    drop_ratio_.Apply(1.0f, 1.0f);
+    drop_ratio_.UpdateBase(0.9f);
+  } else {
+    drop_ratio_.Apply(1.0f, 0.0f);
+  }
+  was_below_max_ = accumulator_ < accumulator_max_;
+}
+
+// This function signals when to drop frames to the caller. It makes use of the
+// drop_ratio_ to smooth out the drops over time.
+bool FrameDropper::DropFrame() {
+  if (!enabled_) {
+    return false;
+  }
+  if (drop_next_) {
+    drop_next_ = false;
+    drop_count_ = 0;
+  }
+
+  if (drop_ratio_.filtered() >= 0.5f) {  // Drops per keep
+    // Limit is the number of frames we should drop between each kept frame
+    // to keep our drop ratio. limit is positive in this case.
+    float denom = 1.0f - drop_ratio_.filtered();
+    if (denom < 1e-5) {
+      denom = 1e-5f;
+    }
+    int32_t limit = static_cast<int32_t>(1.0f / denom - 1.0f + 0.5f);
+    // Put a bound on the max amount of dropped frames between each kept
+    // frame, in terms of frame rate and window size (secs).
+    int max_limit =
+        static_cast<int>(incoming_frame_rate_ * max_drop_duration_secs_);
+    if (limit > max_limit) {
+      limit = max_limit;
+    }
+    if (drop_count_ < 0) {
+      // Reset the drop_count_ since it was negative and should be positive.
+      drop_count_ = -drop_count_;
+    }
+    if (drop_count_ < limit) {
+      // As long we are below the limit we should drop frames.
+      drop_count_++;
+      return true;
+    } else {
+      // Only when we reset drop_count_ a frame should be kept.
+      drop_count_ = 0;
+      return false;
+    }
+  } else if (drop_ratio_.filtered() > 0.0f &&
+             drop_ratio_.filtered() < 0.5f) {  // Keeps per drop
+    // Limit is the number of frames we should keep between each drop
+    // in order to keep the drop ratio. limit is negative in this case,
+    // and the drop_count_ is also negative.
+    float denom = drop_ratio_.filtered();
+    if (denom < 1e-5) {
+      denom = 1e-5f;
+    }
+    int32_t limit = -static_cast<int32_t>(1.0f / denom - 1.0f + 0.5f);
+    if (drop_count_ > 0) {
+      // Reset the drop_count_ since we have a positive
+      // drop_count_, and it should be negative.
+      drop_count_ = -drop_count_;
+    }
+    if (drop_count_ > limit) {
+      if (drop_count_ == 0) {
+        // Drop frames when we reset drop_count_.
+        drop_count_--;
+        return true;
+      } else {
+        // Keep frames as long as we haven't reached limit.
+        drop_count_--;
+        return false;
+      }
+    } else {
+      drop_count_ = 0;
+      return false;
+    }
+  }
+  drop_count_ = 0;
+  return false;
+}
+
+void FrameDropper::SetRates(float bitrate, float incoming_frame_rate) {
+  // Bit rate of -1 means infinite bandwidth.
+  accumulator_max_ = bitrate * kLeakyBucketSizeSeconds;
+  if (target_bitrate_ > 0.0f && bitrate < target_bitrate_ &&
+      accumulator_ > accumulator_max_) {
+    // Rescale the accumulator level if the accumulator max decreases
+    accumulator_ = bitrate / target_bitrate_ * accumulator_;
+  }
+  target_bitrate_ = bitrate;
+  CapAccumulator();
+  incoming_frame_rate_ = incoming_frame_rate;
+}
+
+// Put a cap on the accumulator, i.e., don't let it grow beyond some level.
+// This is a temporary fix for screencasting where very large frames from
+// encoder will cause very slow response (too many frame drops).
+// TODO(isheriff): Remove this now that large delta frames are also spread out ?
+void FrameDropper::CapAccumulator() {
+  float max_accumulator = target_bitrate_ * kAccumulatorCapBufferSizeSecs;
+  if (accumulator_ > max_accumulator) {
+    accumulator_ = max_accumulator;
+  }
+}
+}  // namespace webrtc