Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 593 insertions, 0 deletions

diff --git a/third_party/libwebrtc/call/bitrate_allocator.cc b/third_party/libwebrtc/call/bitrate_allocator.cc
new file mode 100644
index 0000000000..2684a1650e
--- /dev/null
+++ b/third_party/libwebrtc/call/bitrate_allocator.cc
@@ -0,0 +1,593 @@
+/*
+ *  Copyright (c) 2015 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 "call/bitrate_allocator.h"
+
+#include <algorithm>
+#include <cmath>
+#include <memory>
+#include <utility>
+
+#include "absl/algorithm/container.h"
+#include "api/units/data_rate.h"
+#include "api/units/time_delta.h"
+#include "rtc_base/checks.h"
+#include "rtc_base/logging.h"
+#include "rtc_base/numerics/safe_minmax.h"
+#include "system_wrappers/include/clock.h"
+#include "system_wrappers/include/metrics.h"
+
+namespace webrtc {
+
+namespace {
+using bitrate_allocator_impl::AllocatableTrack;
+
+// Allow packets to be transmitted in up to 2 times max video bitrate if the
+// bandwidth estimate allows it.
+const uint8_t kTransmissionMaxBitrateMultiplier = 2;
+const int kDefaultBitrateBps = 300000;
+
+// Require a bitrate increase of max(10%, 20kbps) to resume paused streams.
+const double kToggleFactor = 0.1;
+const uint32_t kMinToggleBitrateBps = 20000;
+
+const int64_t kBweLogIntervalMs = 5000;
+
+double MediaRatio(uint32_t allocated_bitrate, uint32_t protection_bitrate) {
+  RTC_DCHECK_GT(allocated_bitrate, 0);
+  if (protection_bitrate == 0)
+    return 1.0;
+
+  uint32_t media_bitrate = allocated_bitrate - protection_bitrate;
+  return media_bitrate / static_cast<double>(allocated_bitrate);
+}
+
+bool EnoughBitrateForAllObservers(
+    const std::vector<AllocatableTrack>& allocatable_tracks,
+    uint32_t bitrate,
+    uint32_t sum_min_bitrates) {
+  if (bitrate < sum_min_bitrates)
+    return false;
+
+  uint32_t extra_bitrate_per_observer =
+      (bitrate - sum_min_bitrates) /
+      static_cast<uint32_t>(allocatable_tracks.size());
+  for (const auto& observer_config : allocatable_tracks) {
+    if (observer_config.config.min_bitrate_bps + extra_bitrate_per_observer <
+        observer_config.MinBitrateWithHysteresis()) {
+      return false;
+    }
+  }
+  return true;
+}
+
+// Splits `bitrate` evenly to observers already in `allocation`.
+// `include_zero_allocations` decides if zero allocations should be part of
+// the distribution or not. The allowed max bitrate is `max_multiplier` x
+// observer max bitrate.
+void DistributeBitrateEvenly(
+    const std::vector<AllocatableTrack>& allocatable_tracks,
+    uint32_t bitrate,
+    bool include_zero_allocations,
+    int max_multiplier,
+    std::map<BitrateAllocatorObserver*, int>* allocation) {
+  RTC_DCHECK_EQ(allocation->size(), allocatable_tracks.size());
+
+  std::multimap<uint32_t, const AllocatableTrack*> list_max_bitrates;
+  for (const auto& observer_config : allocatable_tracks) {
+    if (include_zero_allocations ||
+        allocation->at(observer_config.observer) != 0) {
+      list_max_bitrates.insert(
+          {observer_config.config.max_bitrate_bps, &observer_config});
+    }
+  }
+  auto it = list_max_bitrates.begin();
+  while (it != list_max_bitrates.end()) {
+    RTC_DCHECK_GT(bitrate, 0);
+    uint32_t extra_allocation =
+        bitrate / static_cast<uint32_t>(list_max_bitrates.size());
+    uint32_t total_allocation =
+        extra_allocation + allocation->at(it->second->observer);
+    bitrate -= extra_allocation;
+    if (total_allocation > max_multiplier * it->first) {
+      // There is more than we can fit for this observer, carry over to the
+      // remaining observers.
+      bitrate += total_allocation - max_multiplier * it->first;
+      total_allocation = max_multiplier * it->first;
+    }
+    // Finally, update the allocation for this observer.
+    allocation->at(it->second->observer) = total_allocation;
+    it = list_max_bitrates.erase(it);
+  }
+}
+
+// From the available `bitrate`, each observer will be allocated a
+// proportional amount based upon its bitrate priority. If that amount is
+// more than the observer's capacity, it will be allocated its capacity, and
+// the excess bitrate is still allocated proportionally to other observers.
+// Allocating the proportional amount means an observer with twice the
+// bitrate_priority of another will be allocated twice the bitrate.
+void DistributeBitrateRelatively(
+    const std::vector<AllocatableTrack>& allocatable_tracks,
+    uint32_t remaining_bitrate,
+    const std::map<BitrateAllocatorObserver*, int>& observers_capacities,
+    std::map<BitrateAllocatorObserver*, int>* allocation) {
+  RTC_DCHECK_EQ(allocation->size(), allocatable_tracks.size());
+  RTC_DCHECK_EQ(observers_capacities.size(), allocatable_tracks.size());
+
+  struct PriorityRateObserverConfig {
+    BitrateAllocatorObserver* allocation_key;
+    // The amount of bitrate bps that can be allocated to this observer.
+    int capacity_bps;
+    double bitrate_priority;
+  };
+
+  double bitrate_priority_sum = 0;
+  std::vector<PriorityRateObserverConfig> priority_rate_observers;
+  for (const auto& observer_config : allocatable_tracks) {
+    priority_rate_observers.push_back(PriorityRateObserverConfig{
+        observer_config.observer,
+        observers_capacities.at(observer_config.observer),
+        observer_config.config.bitrate_priority});
+    bitrate_priority_sum += observer_config.config.bitrate_priority;
+  }
+
+  // Iterate in the order observers can be allocated their full capacity.
+
+  // We want to sort by which observers will be allocated their full capacity
+  // first. By dividing each observer's capacity by its bitrate priority we
+  // are "normalizing" the capacity of an observer by the rate it will be
+  // filled. This is because the amount allocated is based upon bitrate
+  // priority. We allocate twice as much bitrate to an observer with twice the
+  // bitrate priority of another.
+  absl::c_sort(priority_rate_observers, [](const auto& a, const auto& b) {
+    return a.capacity_bps / a.bitrate_priority <
+           b.capacity_bps / b.bitrate_priority;
+  });
+  size_t i;
+  for (i = 0; i < priority_rate_observers.size(); ++i) {
+    const auto& priority_rate_observer = priority_rate_observers[i];
+    // We allocate the full capacity to an observer only if its relative
+    // portion from the remaining bitrate is sufficient to allocate its full
+    // capacity. This means we aren't greedily allocating the full capacity, but
+    // that it is only done when there is also enough bitrate to allocate the
+    // proportional amounts to all other observers.
+    double observer_share =
+        priority_rate_observer.bitrate_priority / bitrate_priority_sum;
+    double allocation_bps = observer_share * remaining_bitrate;
+    bool enough_bitrate = allocation_bps >= priority_rate_observer.capacity_bps;
+    if (!enough_bitrate)
+      break;
+    allocation->at(priority_rate_observer.allocation_key) +=
+        priority_rate_observer.capacity_bps;
+    remaining_bitrate -= priority_rate_observer.capacity_bps;
+    bitrate_priority_sum -= priority_rate_observer.bitrate_priority;
+  }
+
+  // From the remaining bitrate, allocate the proportional amounts to the
+  // observers that aren't allocated their max capacity.
+  for (; i < priority_rate_observers.size(); ++i) {
+    const auto& priority_rate_observer = priority_rate_observers[i];
+    double fraction_allocated =
+        priority_rate_observer.bitrate_priority / bitrate_priority_sum;
+    allocation->at(priority_rate_observer.allocation_key) +=
+        fraction_allocated * remaining_bitrate;
+  }
+}
+
+// Allocates bitrate to observers when there isn't enough to allocate the
+// minimum to all observers.
+std::map<BitrateAllocatorObserver*, int> LowRateAllocation(
+    const std::vector<AllocatableTrack>& allocatable_tracks,
+    uint32_t bitrate) {
+  std::map<BitrateAllocatorObserver*, int> allocation;
+  // Start by allocating bitrate to observers enforcing a min bitrate, hence
+  // remaining_bitrate might turn negative.
+  int64_t remaining_bitrate = bitrate;
+  for (const auto& observer_config : allocatable_tracks) {
+    int32_t allocated_bitrate = 0;
+    if (observer_config.config.enforce_min_bitrate)
+      allocated_bitrate = observer_config.config.min_bitrate_bps;
+
+    allocation[observer_config.observer] = allocated_bitrate;
+    remaining_bitrate -= allocated_bitrate;
+  }
+
+  // Allocate bitrate to all previously active streams.
+  if (remaining_bitrate > 0) {
+    for (const auto& observer_config : allocatable_tracks) {
+      if (observer_config.config.enforce_min_bitrate ||
+          observer_config.LastAllocatedBitrate() == 0)
+        continue;
+
+      uint32_t required_bitrate = observer_config.MinBitrateWithHysteresis();
+      if (remaining_bitrate >= required_bitrate) {
+        allocation[observer_config.observer] = required_bitrate;
+        remaining_bitrate -= required_bitrate;
+      }
+    }
+  }
+
+  // Allocate bitrate to previously paused streams.
+  if (remaining_bitrate > 0) {
+    for (const auto& observer_config : allocatable_tracks) {
+      if (observer_config.LastAllocatedBitrate() != 0)
+        continue;
+
+      // Add a hysteresis to avoid toggling.
+      uint32_t required_bitrate = observer_config.MinBitrateWithHysteresis();
+      if (remaining_bitrate >= required_bitrate) {
+        allocation[observer_config.observer] = required_bitrate;
+        remaining_bitrate -= required_bitrate;
+      }
+    }
+  }
+
+  // Split a possible remainder evenly on all streams with an allocation.
+  if (remaining_bitrate > 0)
+    DistributeBitrateEvenly(allocatable_tracks, remaining_bitrate, false, 1,
+                            &allocation);
+
+  RTC_DCHECK_EQ(allocation.size(), allocatable_tracks.size());
+  return allocation;
+}
+
+// Allocates bitrate to all observers when the available bandwidth is enough
+// to allocate the minimum to all observers but not enough to allocate the
+// max bitrate of each observer.
+
+// Allocates the bitrate based on the bitrate priority of each observer. This
+// bitrate priority defines the priority for bitrate to be allocated to that
+// observer in relation to other observers. For example with two observers, if
+// observer 1 had a bitrate_priority = 1.0, and observer 2 has a
+// bitrate_priority = 2.0, the expected behavior is that observer 2 will be
+// allocated twice the bitrate as observer 1 above the each observer's
+// min_bitrate_bps values, until one of the observers hits its max_bitrate_bps.
+std::map<BitrateAllocatorObserver*, int> NormalRateAllocation(
+    const std::vector<AllocatableTrack>& allocatable_tracks,
+    uint32_t bitrate,
+    uint32_t sum_min_bitrates) {
+  std::map<BitrateAllocatorObserver*, int> allocation;
+  std::map<BitrateAllocatorObserver*, int> observers_capacities;
+  for (const auto& observer_config : allocatable_tracks) {
+    allocation[observer_config.observer] =
+        observer_config.config.min_bitrate_bps;
+    observers_capacities[observer_config.observer] =
+        observer_config.config.max_bitrate_bps -
+        observer_config.config.min_bitrate_bps;
+  }
+
+  bitrate -= sum_min_bitrates;
+
+  // TODO(srte): Implement fair sharing between prioritized streams, currently
+  // they are treated on a first come first serve basis.
+  for (const auto& observer_config : allocatable_tracks) {
+    int64_t priority_margin = observer_config.config.priority_bitrate_bps -
+                              allocation[observer_config.observer];
+    if (priority_margin > 0 && bitrate > 0) {
+      int64_t extra_bitrate = std::min<int64_t>(priority_margin, bitrate);
+      allocation[observer_config.observer] +=
+          rtc::dchecked_cast<int>(extra_bitrate);
+      observers_capacities[observer_config.observer] -= extra_bitrate;
+      bitrate -= extra_bitrate;
+    }
+  }
+
+  // From the remaining bitrate, allocate a proportional amount to each observer
+  // above the min bitrate already allocated.
+  if (bitrate > 0)
+    DistributeBitrateRelatively(allocatable_tracks, bitrate,
+                                observers_capacities, &allocation);
+
+  return allocation;
+}
+
+// Allocates bitrate to observers when there is enough available bandwidth
+// for all observers to be allocated their max bitrate.
+std::map<BitrateAllocatorObserver*, int> MaxRateAllocation(
+    const std::vector<AllocatableTrack>& allocatable_tracks,
+    uint32_t bitrate,
+    uint32_t sum_max_bitrates) {
+  std::map<BitrateAllocatorObserver*, int> allocation;
+
+  for (const auto& observer_config : allocatable_tracks) {
+    allocation[observer_config.observer] =
+        observer_config.config.max_bitrate_bps;
+    bitrate -= observer_config.config.max_bitrate_bps;
+  }
+  DistributeBitrateEvenly(allocatable_tracks, bitrate, true,
+                          kTransmissionMaxBitrateMultiplier, &allocation);
+  return allocation;
+}
+
+// Allocates zero bitrate to all observers.
+std::map<BitrateAllocatorObserver*, int> ZeroRateAllocation(
+    const std::vector<AllocatableTrack>& allocatable_tracks) {
+  std::map<BitrateAllocatorObserver*, int> allocation;
+  for (const auto& observer_config : allocatable_tracks)
+    allocation[observer_config.observer] = 0;
+  return allocation;
+}
+
+std::map<BitrateAllocatorObserver*, int> AllocateBitrates(
+    const std::vector<AllocatableTrack>& allocatable_tracks,
+    uint32_t bitrate) {
+  if (allocatable_tracks.empty())
+    return std::map<BitrateAllocatorObserver*, int>();
+
+  if (bitrate == 0)
+    return ZeroRateAllocation(allocatable_tracks);
+
+  uint32_t sum_min_bitrates = 0;
+  uint32_t sum_max_bitrates = 0;
+  for (const auto& observer_config : allocatable_tracks) {
+    sum_min_bitrates += observer_config.config.min_bitrate_bps;
+    sum_max_bitrates += observer_config.config.max_bitrate_bps;
+  }
+
+  // Not enough for all observers to get an allocation, allocate according to:
+  // enforced min bitrate -> allocated bitrate previous round -> restart paused
+  // streams.
+  if (!EnoughBitrateForAllObservers(allocatable_tracks, bitrate,
+                                    sum_min_bitrates))
+    return LowRateAllocation(allocatable_tracks, bitrate);
+
+  // All observers will get their min bitrate plus a share of the rest. This
+  // share is allocated to each observer based on its bitrate_priority.
+  if (bitrate <= sum_max_bitrates)
+    return NormalRateAllocation(allocatable_tracks, bitrate, sum_min_bitrates);
+
+  // All observers will get up to transmission_max_bitrate_multiplier_ x max.
+  return MaxRateAllocation(allocatable_tracks, bitrate, sum_max_bitrates);
+}
+
+}  // namespace
+
+BitrateAllocator::BitrateAllocator(LimitObserver* limit_observer)
+    : limit_observer_(limit_observer),
+      last_target_bps_(0),
+      last_stable_target_bps_(0),
+      last_non_zero_bitrate_bps_(kDefaultBitrateBps),
+      last_fraction_loss_(0),
+      last_rtt_(0),
+      last_bwe_period_ms_(1000),
+      num_pause_events_(0),
+      last_bwe_log_time_(0) {
+  sequenced_checker_.Detach();
+}
+
+BitrateAllocator::~BitrateAllocator() {
+  RTC_HISTOGRAM_COUNTS_100("WebRTC.Call.NumberOfPauseEvents",
+                           num_pause_events_);
+}
+
+void BitrateAllocator::UpdateStartRate(uint32_t start_rate_bps) {
+  RTC_DCHECK_RUN_ON(&sequenced_checker_);
+  last_non_zero_bitrate_bps_ = start_rate_bps;
+}
+
+void BitrateAllocator::OnNetworkEstimateChanged(TargetTransferRate msg) {
+  RTC_DCHECK_RUN_ON(&sequenced_checker_);
+  last_target_bps_ = msg.target_rate.bps();
+  last_stable_target_bps_ = msg.stable_target_rate.bps();
+  last_non_zero_bitrate_bps_ =
+      last_target_bps_ > 0 ? last_target_bps_ : last_non_zero_bitrate_bps_;
+
+  int loss_ratio_255 = msg.network_estimate.loss_rate_ratio * 255;
+  last_fraction_loss_ =
+      rtc::dchecked_cast<uint8_t>(rtc::SafeClamp(loss_ratio_255, 0, 255));
+  last_rtt_ = msg.network_estimate.round_trip_time.ms();
+  last_bwe_period_ms_ = msg.network_estimate.bwe_period.ms();
+
+  // Periodically log the incoming BWE.
+  int64_t now = msg.at_time.ms();
+  if (now > last_bwe_log_time_ + kBweLogIntervalMs) {
+    RTC_LOG(LS_INFO) << "Current BWE " << last_target_bps_;
+    last_bwe_log_time_ = now;
+  }
+
+  auto allocation = AllocateBitrates(allocatable_tracks_, last_target_bps_);
+  auto stable_bitrate_allocation =
+      AllocateBitrates(allocatable_tracks_, last_stable_target_bps_);
+
+  for (auto& config : allocatable_tracks_) {
+    uint32_t allocated_bitrate = allocation[config.observer];
+    uint32_t allocated_stable_target_rate =
+        stable_bitrate_allocation[config.observer];
+    BitrateAllocationUpdate update;
+    update.target_bitrate = DataRate::BitsPerSec(allocated_bitrate);
+    update.stable_target_bitrate =
+        DataRate::BitsPerSec(allocated_stable_target_rate);
+    update.packet_loss_ratio = last_fraction_loss_ / 256.0;
+    update.round_trip_time = TimeDelta::Millis(last_rtt_);
+    update.bwe_period = TimeDelta::Millis(last_bwe_period_ms_);
+    update.cwnd_reduce_ratio = msg.cwnd_reduce_ratio;
+    uint32_t protection_bitrate = config.observer->OnBitrateUpdated(update);
+
+    if (allocated_bitrate == 0 && config.allocated_bitrate_bps > 0) {
+      if (last_target_bps_ > 0)
+        ++num_pause_events_;
+      // The protection bitrate is an estimate based on the ratio between media
+      // and protection used before this observer was muted.
+      uint32_t predicted_protection_bps =
+          (1.0 - config.media_ratio) * config.config.min_bitrate_bps;
+      RTC_LOG(LS_INFO) << "Pausing observer " << config.observer
+                       << " with configured min bitrate "
+                       << config.config.min_bitrate_bps
+                       << " and current estimate of " << last_target_bps_
+                       << " and protection bitrate "
+                       << predicted_protection_bps;
+    } else if (allocated_bitrate > 0 && config.allocated_bitrate_bps == 0) {
+      if (last_target_bps_ > 0)
+        ++num_pause_events_;
+      RTC_LOG(LS_INFO) << "Resuming observer " << config.observer
+                       << ", configured min bitrate "
+                       << config.config.min_bitrate_bps
+                       << ", current allocation " << allocated_bitrate
+                       << " and protection bitrate " << protection_bitrate;
+    }
+
+    // Only update the media ratio if the observer got an allocation.
+    if (allocated_bitrate > 0)
+      config.media_ratio = MediaRatio(allocated_bitrate, protection_bitrate);
+    config.allocated_bitrate_bps = allocated_bitrate;
+  }
+  UpdateAllocationLimits();
+}
+
+void BitrateAllocator::AddObserver(BitrateAllocatorObserver* observer,
+                                   MediaStreamAllocationConfig config) {
+  RTC_DCHECK_RUN_ON(&sequenced_checker_);
+  RTC_DCHECK_GT(config.bitrate_priority, 0);
+  RTC_DCHECK(std::isnormal(config.bitrate_priority));
+  auto it = absl::c_find_if(
+      allocatable_tracks_,
+      [observer](const auto& config) { return config.observer == observer; });
+  // Update settings if the observer already exists, create a new one otherwise.
+  if (it != allocatable_tracks_.end()) {
+    it->config = config;
+  } else {
+    allocatable_tracks_.push_back(AllocatableTrack(observer, config));
+  }
+
+  if (last_target_bps_ > 0) {
+    // Calculate a new allocation and update all observers.
+
+    auto allocation = AllocateBitrates(allocatable_tracks_, last_target_bps_);
+    auto stable_bitrate_allocation =
+        AllocateBitrates(allocatable_tracks_, last_stable_target_bps_);
+    for (auto& config : allocatable_tracks_) {
+      uint32_t allocated_bitrate = allocation[config.observer];
+      uint32_t allocated_stable_bitrate =
+          stable_bitrate_allocation[config.observer];
+      BitrateAllocationUpdate update;
+      update.target_bitrate = DataRate::BitsPerSec(allocated_bitrate);
+      update.stable_target_bitrate =
+          DataRate::BitsPerSec(allocated_stable_bitrate);
+      update.packet_loss_ratio = last_fraction_loss_ / 256.0;
+      update.round_trip_time = TimeDelta::Millis(last_rtt_);
+      update.bwe_period = TimeDelta::Millis(last_bwe_period_ms_);
+      uint32_t protection_bitrate = config.observer->OnBitrateUpdated(update);
+      config.allocated_bitrate_bps = allocated_bitrate;
+      if (allocated_bitrate > 0)
+        config.media_ratio = MediaRatio(allocated_bitrate, protection_bitrate);
+    }
+  } else {
+    // Currently, an encoder is not allowed to produce frames.
+    // But we still have to return the initial config bitrate + let the
+    // observer know that it can not produce frames.
+
+    BitrateAllocationUpdate update;
+    update.target_bitrate = DataRate::Zero();
+    update.stable_target_bitrate = DataRate::Zero();
+    update.packet_loss_ratio = last_fraction_loss_ / 256.0;
+    update.round_trip_time = TimeDelta::Millis(last_rtt_);
+    update.bwe_period = TimeDelta::Millis(last_bwe_period_ms_);
+    observer->OnBitrateUpdated(update);
+  }
+  UpdateAllocationLimits();
+}
+
+void BitrateAllocator::UpdateAllocationLimits() {
+  BitrateAllocationLimits limits;
+  for (const auto& config : allocatable_tracks_) {
+    uint32_t stream_padding = config.config.pad_up_bitrate_bps;
+    if (config.config.enforce_min_bitrate) {
+      limits.min_allocatable_rate +=
+          DataRate::BitsPerSec(config.config.min_bitrate_bps);
+    } else if (config.allocated_bitrate_bps == 0) {
+      stream_padding =
+          std::max(config.MinBitrateWithHysteresis(), stream_padding);
+    }
+    limits.max_padding_rate += DataRate::BitsPerSec(stream_padding);
+    limits.max_allocatable_rate +=
+        DataRate::BitsPerSec(config.config.max_bitrate_bps);
+  }
+
+  if (limits.min_allocatable_rate == current_limits_.min_allocatable_rate &&
+      limits.max_allocatable_rate == current_limits_.max_allocatable_rate &&
+      limits.max_padding_rate == current_limits_.max_padding_rate) {
+    return;
+  }
+  current_limits_ = limits;
+
+  RTC_LOG(LS_INFO) << "UpdateAllocationLimits : total_requested_min_bitrate: "
+                   << ToString(limits.min_allocatable_rate)
+                   << ", total_requested_padding_bitrate: "
+                   << ToString(limits.max_padding_rate)
+                   << ", total_requested_max_bitrate: "
+                   << ToString(limits.max_allocatable_rate);
+
+  limit_observer_->OnAllocationLimitsChanged(limits);
+}
+
+void BitrateAllocator::RemoveObserver(BitrateAllocatorObserver* observer) {
+  RTC_DCHECK_RUN_ON(&sequenced_checker_);
+  for (auto it = allocatable_tracks_.begin(); it != allocatable_tracks_.end();
+       ++it) {
+    if (it->observer == observer) {
+      allocatable_tracks_.erase(it);
+      break;
+    }
+  }
+
+  UpdateAllocationLimits();
+}
+
+int BitrateAllocator::GetStartBitrate(
+    BitrateAllocatorObserver* observer) const {
+  RTC_DCHECK_RUN_ON(&sequenced_checker_);
+  auto it = absl::c_find_if(
+      allocatable_tracks_,
+      [observer](const auto& config) { return config.observer == observer; });
+  if (it == allocatable_tracks_.end()) {
+    // This observer hasn't been added yet, just give it its fair share.
+    return last_non_zero_bitrate_bps_ /
+           static_cast<int>((allocatable_tracks_.size() + 1));
+  } else if (it->allocated_bitrate_bps == -1) {
+    // This observer hasn't received an allocation yet, so do the same.
+    return last_non_zero_bitrate_bps_ /
+           static_cast<int>(allocatable_tracks_.size());
+  } else {
+    // This observer already has an allocation.
+    return it->allocated_bitrate_bps;
+  }
+}
+
+uint32_t bitrate_allocator_impl::AllocatableTrack::LastAllocatedBitrate()
+    const {
+  // Return the configured minimum bitrate for newly added observers, to avoid
+  // requiring an extra high bitrate for the observer to get an allocated
+  // bitrate.
+  return allocated_bitrate_bps == -1 ? config.min_bitrate_bps
+                                     : allocated_bitrate_bps;
+}
+
+uint32_t bitrate_allocator_impl::AllocatableTrack::MinBitrateWithHysteresis()
+    const {
+  uint32_t min_bitrate = config.min_bitrate_bps;
+  if (LastAllocatedBitrate() == 0) {
+    min_bitrate += std::max(static_cast<uint32_t>(kToggleFactor * min_bitrate),
+                            kMinToggleBitrateBps);
+  }
+  // Account for protection bitrate used by this observer in the previous
+  // allocation.
+  // Note: the ratio will only be updated when the stream is active, meaning a
+  // paused stream won't get any ratio updates. This might lead to waiting a bit
+  // longer than necessary if the network condition improves, but this is to
+  // avoid too much toggling.
+  if (media_ratio > 0.0 && media_ratio < 1.0)
+    min_bitrate += min_bitrate * (1.0 - media_ratio);
+
+  return min_bitrate;
+}
+
+}  // namespace webrtc