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/*
* 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