webrtc_m130/video/frame_cadence_adapter.cc

/*
 *  Copyright (c) 2021 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 "video/frame_cadence_adapter.h"

#include <algorithm>
#include <atomic>
#include <cstdint>
#include <deque>
#include <memory>
#include <utility>
#include <vector>

#include "absl/algorithm/container.h"
#include "absl/base/attributes.h"
#include "absl/cleanup/cleanup.h"
#include "api/sequence_checker.h"
#include "api/task_queue/pending_task_safety_flag.h"
#include "api/task_queue/task_queue_base.h"
#include "api/units/time_delta.h"
#include "api/units/timestamp.h"
#include "api/video/video_frame.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
#include "rtc_base/race_checker.h"
#include "rtc_base/rate_statistics.h"
#include "rtc_base/synchronization/mutex.h"
#include "rtc_base/system/no_unique_address.h"
#include "rtc_base/system/unused.h"
#include "rtc_base/task_utils/repeating_task.h"
#include "rtc_base/thread_annotations.h"
#include "rtc_base/time_utils.h"
#include "rtc_base/trace_event.h"
#include "system_wrappers/include/clock.h"
#include "system_wrappers/include/metrics.h"
#include "system_wrappers/include/ntp_time.h"

namespace webrtc {
namespace {

// Abstracts concrete modes of the cadence adapter.
class AdapterMode {
 public:
  virtual ~AdapterMode() = default;

  // Called on the worker thread for every frame that enters.
  virtual void OnFrame(Timestamp post_time,
                       bool queue_overload,
                       const VideoFrame& frame) = 0;

  // Returns the currently estimated input framerate.
  virtual absl::optional<uint32_t> GetInputFrameRateFps() = 0;

  // Updates the frame rate.
  virtual void UpdateFrameRate(Timestamp frame_timestamp) = 0;
};

// Implements a pass-through adapter. Single-threaded.
class PassthroughAdapterMode : public AdapterMode {
 public:
  explicit PassthroughAdapterMode(
      FrameCadenceAdapterInterface::Callback* callback)
      : callback_(callback) {
    sequence_checker_.Detach();
  }

  // Adapter overrides.
  void OnFrame(Timestamp post_time,
               bool queue_overload,
               const VideoFrame& frame) override {
    RTC_DCHECK_RUN_ON(&sequence_checker_);
    callback_->OnFrame(post_time, queue_overload, frame);
  }

  absl::optional<uint32_t> GetInputFrameRateFps() override {
    RTC_DCHECK_RUN_ON(&sequence_checker_);
    return last_frame_rate_;
  }

  void UpdateFrameRate(Timestamp frame_timestamp) override {
    RTC_DCHECK_RUN_ON(&sequence_checker_);
    // RateStatistics will calculate a too high rate immediately after Update.
    last_frame_rate_ = input_framerate_.Rate(frame_timestamp.ms());
    input_framerate_.Update(1, frame_timestamp.ms());
  }

 private:
  absl::optional<uint64_t> last_frame_rate_;
  FrameCadenceAdapterInterface::Callback* const callback_;
  RTC_NO_UNIQUE_ADDRESS SequenceChecker sequence_checker_;
  // Input frame rate statistics for use when not in zero-hertz mode.
  RateStatistics input_framerate_ RTC_GUARDED_BY(sequence_checker_){
      FrameCadenceAdapterInterface::kFrameRateAveragingWindowSizeMs, 1000};
};

// Implements a frame cadence adapter supporting zero-hertz input.
class ZeroHertzAdapterMode : public AdapterMode {
 public:
  ZeroHertzAdapterMode(TaskQueueBase* queue,
                       Clock* clock,
                       FrameCadenceAdapterInterface::Callback* callback,
                       double max_fps,
                       std::atomic<int>& frames_scheduled_for_processing,
                       bool zero_hertz_queue_overload);
  ~ZeroHertzAdapterMode() { refresh_frame_requester_.Stop(); }

  // Reconfigures according to parameters.
  // All spatial layer trackers are initialized as unconverged by this method.
  void ReconfigureParameters(
      const FrameCadenceAdapterInterface::ZeroHertzModeParams& params);

  // Updates spatial layer quality convergence status.
  void UpdateLayerQualityConvergence(size_t spatial_index,
                                     bool quality_converged);

  // Updates spatial layer enabled status.
  void UpdateLayerStatus(size_t spatial_index, bool enabled);

  // Adapter overrides.
  void OnFrame(Timestamp post_time,
               bool queue_overload,
               const VideoFrame& frame) override;
  absl::optional<uint32_t> GetInputFrameRateFps() override;
  void UpdateFrameRate(Timestamp frame_timestamp) override {}

  // Notified on dropped frames.
  void OnDiscardedFrame();

  // Conditionally requests a refresh frame via
  // Callback::RequestRefreshFrame.
  void ProcessKeyFrameRequest();

  // Updates the restrictions of max frame rate for the video source.
  // Always called during construction using latest `restricted_frame_delay_`.
  void UpdateVideoSourceRestrictions(absl::optional<double> max_frame_rate);

 private:
  // The tracking state of each spatial layer. Used for determining when to
  // stop repeating frames.
  struct SpatialLayerTracker {
    // If unset, the layer is disabled. Otherwise carries the quality
    // convergence status of the layer.
    absl::optional<bool> quality_converged;
  };
  // The state of a scheduled repeat.
  struct ScheduledRepeat {
    ScheduledRepeat(Timestamp origin,
                    int64_t origin_timestamp_us,
                    int64_t origin_ntp_time_ms)
        : scheduled(origin),
          idle(false),
          origin(origin),
          origin_timestamp_us(origin_timestamp_us),
          origin_ntp_time_ms(origin_ntp_time_ms) {}
    // The instant when the repeat was scheduled.
    Timestamp scheduled;
    // True if the repeat was scheduled as an idle repeat (long), false
    // otherwise.
    bool idle;
    // The moment we decided to start repeating.
    Timestamp origin;
    // The timestamp_us of the frame when we started repeating.
    int64_t origin_timestamp_us;
    // The ntp_times_ms of the frame when we started repeating.
    int64_t origin_ntp_time_ms;
  };

  // Returns true if all spatial layers can be considered to be converged in
  // terms of quality.
  // Convergence means QP has dropped to a low-enough level to warrant ceasing
  // to send identical frames at high frequency.
  bool HasQualityConverged() const RTC_RUN_ON(sequence_checker_);
  // Resets quality convergence information. HasQualityConverged() returns false
  // after this call.
  void ResetQualityConvergenceInfo() RTC_RUN_ON(sequence_checker_);
  // Processes incoming frames on a delayed cadence.
  void ProcessOnDelayedCadence(Timestamp post_time)
      RTC_RUN_ON(sequence_checker_);
  // Schedules a later repeat with delay depending on state of layer trackers
  // and if UpdateVideoSourceRestrictions has been called or not.
  // If true is passed in `idle_repeat`, the repeat is going to be
  // kZeroHertzIdleRepeatRatePeriod. Otherwise it'll be the maximum value of
  // `frame_delay` or `restricted_frame_delay_` if it has been set.
  void ScheduleRepeat(int frame_id, bool idle_repeat)
      RTC_RUN_ON(sequence_checker_);
  // Repeats a frame in the absence of incoming frames. Slows down when quality
  // convergence is attained, and stops the cadence terminally when new frames
  // have arrived.
  void ProcessRepeatedFrameOnDelayedCadence(int frame_id)
      RTC_RUN_ON(sequence_checker_);
  // Sends a frame, updating the timestamp to the current time. Also updates
  // `queue_overload_count_` based on the time it takes to encode a frame and
  // the amount of received frames while encoding. The `queue_overload`
  // parameter in the OnFrame callback will be true while
  // `queue_overload_count_` is larger than zero to allow the client to drop
  // frames and thereby mitigate delay buildups.
  // Repeated frames are sent with `post_time` set to absl::nullopt.
  void SendFrameNow(absl::optional<Timestamp> post_time,
                    const VideoFrame& frame) RTC_RUN_ON(sequence_checker_);
  // Returns the repeat duration depending on if it's an idle repeat or not.
  TimeDelta RepeatDuration(bool idle_repeat) const
      RTC_RUN_ON(sequence_checker_);
  // Returns the frame duration taking potential restrictions into account.
  TimeDelta FrameDuration() const RTC_RUN_ON(sequence_checker_);
  // Unless timer already running, starts repeatedly requesting refresh frames
  // after a grace_period. If a frame appears before the grace_period has
  // passed, the request is cancelled.
  void MaybeStartRefreshFrameRequester() RTC_RUN_ON(sequence_checker_);

  TaskQueueBase* const queue_;
  Clock* const clock_;
  FrameCadenceAdapterInterface::Callback* const callback_;

  // The configured max_fps.
  // TODO(crbug.com/1255737): support max_fps updates.
  const double max_fps_;

  // Number of frames that are currently scheduled for processing on the
  // `queue_`.
  const std::atomic<int>& frames_scheduled_for_processing_;

  // Can be used as kill-switch for the queue overload mechanism.
  const bool zero_hertz_queue_overload_enabled_;

  // How much the incoming frame sequence is delayed by.
  const TimeDelta frame_delay_ = TimeDelta::Seconds(1) / max_fps_;

  RTC_NO_UNIQUE_ADDRESS SequenceChecker sequence_checker_;
  // A queue of incoming frames and repeated frames.
  std::deque<VideoFrame> queued_frames_ RTC_GUARDED_BY(sequence_checker_);
  // The current frame ID to use when starting to repeat frames. This is used
  // for cancelling deferred repeated frame processing happening.
  int current_frame_id_ RTC_GUARDED_BY(sequence_checker_) = 0;
  // Has content when we are repeating frames.
  absl::optional<ScheduledRepeat> scheduled_repeat_
      RTC_GUARDED_BY(sequence_checker_);
  // Convergent state of each of the configured simulcast layers.
  std::vector<SpatialLayerTracker> layer_trackers_
      RTC_GUARDED_BY(sequence_checker_);
  // Repeating task handle used for requesting refresh frames until arrival, as
  // they can be dropped in various places in the capture pipeline.
  RepeatingTaskHandle refresh_frame_requester_
      RTC_GUARDED_BY(sequence_checker_);
  // Can be set by UpdateVideoSourceRestrictions when the video source restricts
  // the max frame rate.
  absl::optional<TimeDelta> restricted_frame_delay_
      RTC_GUARDED_BY(sequence_checker_);
  // Set in OnSendFrame to reflect how many future frames will be forwarded with
  // the `queue_overload` flag set to true.
  int queue_overload_count_ RTC_GUARDED_BY(sequence_checker_) = 0;

  ScopedTaskSafety safety_;
};

// Implements a frame cadence adapter supporting VSync aligned encoding.
class VSyncEncodeAdapterMode : public AdapterMode {
 public:
  VSyncEncodeAdapterMode(
      Clock* clock,
      TaskQueueBase* queue,
      rtc::scoped_refptr<PendingTaskSafetyFlag> queue_safety_flag,
      Metronome* metronome,
      TaskQueueBase* worker_queue,
      FrameCadenceAdapterInterface::Callback* callback)
      : clock_(clock),
        queue_(queue),
        queue_safety_flag_(queue_safety_flag),
        callback_(callback),
        metronome_(metronome),
        worker_queue_(worker_queue) {
    queue_sequence_checker_.Detach();
    worker_sequence_checker_.Detach();
  }

  void PrepareShutdown() {
    MutexLock lock(&queue_lock_);
    queue_ = nullptr;
  }

  // Adapter overrides.
  void OnFrame(Timestamp post_time,
               bool queue_overload,
               const VideoFrame& frame) override;

  absl::optional<uint32_t> GetInputFrameRateFps() override {
    RTC_DCHECK_RUN_ON(&queue_sequence_checker_);
    return last_frame_rate_;
  }

  void UpdateFrameRate(Timestamp frame_timestamp) override {
    RTC_DCHECK_RUN_ON(&queue_sequence_checker_);
    // RateStatistics will calculate a too high rate immediately after Update.
    last_frame_rate_ = input_framerate_.Rate(frame_timestamp.ms());
    input_framerate_.Update(1, frame_timestamp.ms());
  }

  void EncodeAllEnqueuedFrames();

 private:
  // Holds input frames coming from the client ready to be encoded.
  struct InputFrameRef {
    InputFrameRef(const VideoFrame& video_frame, Timestamp time_when_posted_us)
        : time_when_posted_us(time_when_posted_us),
          video_frame(std::move(video_frame)) {}
    Timestamp time_when_posted_us;
    const VideoFrame video_frame;
  };

  Clock* const clock_;
  // Protects `queue_`.
  // TODO: crbug.com/358040973 - We should eventually figure out a way to avoid
  // lock protection.
  Mutex queue_lock_;
  TaskQueueBase* queue_ RTC_GUARDED_BY(queue_lock_)
      RTC_PT_GUARDED_BY(queue_lock_);
  RTC_NO_UNIQUE_ADDRESS SequenceChecker queue_sequence_checker_;
  rtc::scoped_refptr<PendingTaskSafetyFlag> queue_safety_flag_;
  // Input frame rate statistics for use when not in zero-hertz mode.
  absl::optional<uint64_t> last_frame_rate_
      RTC_GUARDED_BY(queue_sequence_checker_);
  RateStatistics input_framerate_ RTC_GUARDED_BY(queue_sequence_checker_){
      FrameCadenceAdapterInterface::kFrameRateAveragingWindowSizeMs, 1000};
  FrameCadenceAdapterInterface::Callback* const callback_;

  Metronome* metronome_;
  TaskQueueBase* const worker_queue_;
  RTC_NO_UNIQUE_ADDRESS SequenceChecker worker_sequence_checker_;
  // `worker_safety_` protects tasks on the worker queue related to
  // `metronome_` since metronome usage must happen on worker thread.
  ScopedTaskSafetyDetached worker_safety_;
  Timestamp expected_next_tick_ RTC_GUARDED_BY(worker_sequence_checker_) =
      Timestamp::PlusInfinity();
  // Vector of input frames to be encoded.
  std::vector<InputFrameRef> input_queue_
      RTC_GUARDED_BY(worker_sequence_checker_);
};

class FrameCadenceAdapterImpl : public FrameCadenceAdapterInterface {
 public:
  FrameCadenceAdapterImpl(Clock* clock,
                          TaskQueueBase* queue,
                          Metronome* metronome,
                          TaskQueueBase* worker_queue,
                          const FieldTrialsView& field_trials);
  ~FrameCadenceAdapterImpl();

  // FrameCadenceAdapterInterface overrides.
  void Initialize(Callback* callback) override;
  void SetZeroHertzModeEnabled(
      absl::optional<ZeroHertzModeParams> params) override;
  absl::optional<uint32_t> GetInputFrameRateFps() override;
  void UpdateLayerQualityConvergence(size_t spatial_index,
                                     bool quality_converged) override;
  void UpdateLayerStatus(size_t spatial_index, bool enabled) override;
  void UpdateVideoSourceRestrictions(
      absl::optional<double> max_frame_rate) override;
  void ProcessKeyFrameRequest() override;

  // VideoFrameSink overrides.
  void OnFrame(const VideoFrame& frame) override;
  void OnDiscardedFrame() override;
  void OnConstraintsChanged(
      const VideoTrackSourceConstraints& constraints) override;

 private:
  void UpdateFrameRate(Timestamp frame_timestamp);
  // Called from OnFrame in both pass-through and zero-hertz mode.
  void OnFrameOnMainQueue(Timestamp post_time,
                          bool queue_overload,
                          const VideoFrame& frame) RTC_RUN_ON(queue_);

  // Returns true under all of the following conditions:
  // - constraints min fps set to 0
  // - constraints max fps set and greater than 0,
  // - field trial enabled
  // - zero-hertz mode enabled
  bool IsZeroHertzScreenshareEnabled() const RTC_RUN_ON(queue_);

  // Configures current adapter on non-ZeroHertz mode, called when Initialize or
  // MaybeReconfigureAdapters.
  void ConfigureCurrentAdapterWithoutZeroHertz();

  // Handles adapter creation on configuration changes.
  void MaybeReconfigureAdapters(bool was_zero_hertz_enabled) RTC_RUN_ON(queue_);

  Clock* const clock_;
  TaskQueueBase* const queue_;

  // Kill-switch for the queue overload mechanism in zero-hertz mode.
  const bool frame_cadence_adapter_zero_hertz_queue_overload_enabled_;

  // Field trial for using timestamp from video frames, rather than clock when
  // calculating input frame rate.
  const bool use_video_frame_timestamp_;
  // Used for verifying that timestamps are monotonically increasing.
  absl::optional<Timestamp> last_incoming_frame_timestamp_;
  bool incoming_frame_timestamp_monotonically_increasing_ = true;

  // The three possible modes we're under.
  absl::optional<PassthroughAdapterMode> passthrough_adapter_;
  absl::optional<ZeroHertzAdapterMode> zero_hertz_adapter_;
  // The `vsync_encode_adapter_` must be destroyed on the worker queue since
  // VSync metronome needs to happen on worker thread.
  std::unique_ptr<VSyncEncodeAdapterMode> vsync_encode_adapter_;
  // If set, zero-hertz mode has been enabled.
  absl::optional<ZeroHertzModeParams> zero_hertz_params_;
  // Cache for the current adapter mode.
  AdapterMode* current_adapter_mode_ = nullptr;

  // VSync encoding is used when this valid.
  Metronome* const metronome_;
  TaskQueueBase* const worker_queue_;

  // Timestamp for statistics reporting.
  absl::optional<Timestamp> zero_hertz_adapter_created_timestamp_
      RTC_GUARDED_BY(queue_);

  // Set up during Initialize.
  Callback* callback_ = nullptr;

  // The source's constraints.
  absl::optional<VideoTrackSourceConstraints> source_constraints_
      RTC_GUARDED_BY(queue_);

  // Stores the latest restriction in max frame rate set by
  // UpdateVideoSourceRestrictions. Ensures that a previously set restriction
  // can be maintained during reconstructions of the adapter.
  absl::optional<double> restricted_max_frame_rate_ RTC_GUARDED_BY(queue_);

  // Race checker for incoming frames. This is the network thread in chromium,
  // but may vary from test contexts.
  rtc::RaceChecker incoming_frame_race_checker_;

  // Number of frames that are currently scheduled for processing on the
  // `queue_`.
  std::atomic<int> frames_scheduled_for_processing_{0};

  ScopedTaskSafetyDetached safety_;
};

ZeroHertzAdapterMode::ZeroHertzAdapterMode(
    TaskQueueBase* queue,
    Clock* clock,
    FrameCadenceAdapterInterface::Callback* callback,
    double max_fps,
    std::atomic<int>& frames_scheduled_for_processing,
    bool zero_hertz_queue_overload_enabled)
    : queue_(queue),
      clock_(clock),
      callback_(callback),
      max_fps_(max_fps),
      frames_scheduled_for_processing_(frames_scheduled_for_processing),
      zero_hertz_queue_overload_enabled_(zero_hertz_queue_overload_enabled) {
  sequence_checker_.Detach();
  MaybeStartRefreshFrameRequester();
}

void ZeroHertzAdapterMode::ReconfigureParameters(
    const FrameCadenceAdapterInterface::ZeroHertzModeParams& params) {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  RTC_DLOG(LS_INFO) << __func__ << " this " << this << " num_simulcast_layers "
                    << params.num_simulcast_layers;

  // Start as unconverged.
  layer_trackers_.clear();
  layer_trackers_.resize(params.num_simulcast_layers,
                         SpatialLayerTracker{false});
}

void ZeroHertzAdapterMode::UpdateLayerQualityConvergence(
    size_t spatial_index,
    bool quality_converged) {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  TRACE_EVENT_INSTANT2(TRACE_DISABLED_BY_DEFAULT("webrtc"), __func__,
                       TRACE_EVENT_SCOPE_GLOBAL, "spatial_index", spatial_index,
                       "converged", quality_converged);
  if (spatial_index >= layer_trackers_.size())
    return;
  if (layer_trackers_[spatial_index].quality_converged.has_value())
    layer_trackers_[spatial_index].quality_converged = quality_converged;
}

void ZeroHertzAdapterMode::UpdateLayerStatus(size_t spatial_index,
                                             bool enabled) {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  TRACE_EVENT_INSTANT2(TRACE_DISABLED_BY_DEFAULT("webrtc"), __func__,
                       TRACE_EVENT_SCOPE_GLOBAL, "spatial_index", spatial_index,
                       "enabled", enabled);
  if (spatial_index >= layer_trackers_.size())
    return;
  if (enabled) {
    if (!layer_trackers_[spatial_index].quality_converged.has_value()) {
      // Assume quality has not converged until hearing otherwise.
      layer_trackers_[spatial_index].quality_converged = false;
    }
  } else {
    layer_trackers_[spatial_index].quality_converged = absl::nullopt;
  }
}

void ZeroHertzAdapterMode::OnFrame(Timestamp post_time,
                                   bool queue_overload,
                                   const VideoFrame& frame) {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  TRACE_EVENT0("webrtc", "ZeroHertzAdapterMode::OnFrame");
  refresh_frame_requester_.Stop();

  // Assume all enabled layers are unconverged after frame entry.
  ResetQualityConvergenceInfo();

  // Remove stored repeating frame if needed.
  if (scheduled_repeat_.has_value()) {
    RTC_DCHECK(queued_frames_.size() == 1);
    RTC_DLOG(LS_VERBOSE) << __func__ << " this " << this
                         << " cancel repeat and restart with original";
    queued_frames_.pop_front();
  }

  // Store the frame in the queue and schedule deferred processing.
  queued_frames_.push_back(frame);
  current_frame_id_++;
  scheduled_repeat_ = absl::nullopt;
  TimeDelta time_spent_since_post = clock_->CurrentTime() - post_time;
  queue_->PostDelayedHighPrecisionTask(
      SafeTask(safety_.flag(),
               [this, post_time] {
                 RTC_DCHECK_RUN_ON(&sequence_checker_);
                 ProcessOnDelayedCadence(post_time);
               }),
      std::max(frame_delay_ - time_spent_since_post, TimeDelta::Zero()));
}

void ZeroHertzAdapterMode::OnDiscardedFrame() {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  TRACE_EVENT0("webrtc", __func__);

  // Under zero hertz source delivery, a discarded frame ending a sequence of
  // frames which happened to contain important information can be seen as a
  // capture freeze. Avoid this by starting requesting refresh frames after a
  // grace period.
  MaybeStartRefreshFrameRequester();
}

absl::optional<uint32_t> ZeroHertzAdapterMode::GetInputFrameRateFps() {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  return max_fps_;
}

void ZeroHertzAdapterMode::UpdateVideoSourceRestrictions(
    absl::optional<double> max_frame_rate) {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  TRACE_EVENT_INSTANT1(TRACE_DISABLED_BY_DEFAULT("webrtc"), __func__,
                       TRACE_EVENT_SCOPE_GLOBAL, "max_frame_rate",
                       max_frame_rate.value_or(-1));
  if (max_frame_rate.value_or(0) > 0) {
    // Set new, validated (> 0) and restricted frame rate.
    restricted_frame_delay_ = TimeDelta::Seconds(1) / *max_frame_rate;
  } else {
    // Source reports that the frame rate is now unrestricted.
    restricted_frame_delay_ = absl::nullopt;
  }
}

void ZeroHertzAdapterMode::ProcessKeyFrameRequest() {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  TRACE_EVENT_INSTANT0("webrtc", __func__, TRACE_EVENT_SCOPE_GLOBAL);
  // If we're new and don't have a frame, there's no need to request refresh
  // frames as this was being triggered for us when zero-hz mode was set up.
  //
  // The next frame encoded will be a key frame. Reset quality convergence so we
  // don't get idle repeats shortly after, because key frames need a lot of
  // refinement frames.
  ResetQualityConvergenceInfo();

  // If we're not repeating, or we're repeating with short duration, we will
  // very soon send out a frame and don't need a refresh frame.
  if (!scheduled_repeat_.has_value() || !scheduled_repeat_->idle) {
    RTC_LOG(LS_INFO) << __func__ << " this " << this
                     << " not requesting refresh frame because of recently "
                        "incoming frame or short repeating.";
    return;
  }

  // If the repeat is scheduled within a short (i.e. frame_delay_) interval, we
  // will very soon send out a frame and don't need a refresh frame.
  Timestamp now = clock_->CurrentTime();
  if (scheduled_repeat_->scheduled + RepeatDuration(/*idle_repeat=*/true) -
          now <=
      frame_delay_) {
    RTC_LOG(LS_INFO) << __func__ << " this " << this
                     << " not requesting refresh frame because of soon "
                        "happening idle repeat";
    return;
  }

  // Cancel the current repeat and reschedule a short repeat now. No need for a
  // new refresh frame.
  RTC_LOG(LS_INFO) << __func__ << " this " << this
                   << " not requesting refresh frame and scheduling a short "
                      "repeat due to key frame request";
  ScheduleRepeat(++current_frame_id_, /*idle_repeat=*/false);
  return;
}

bool ZeroHertzAdapterMode::HasQualityConverged() const {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  // 1. Define ourselves as unconverged with no spatial layers configured. This
  // is to keep short repeating until the layer configuration comes.
  // 2. Unset layers implicitly imply that they're converged to support
  // disabling layers when they're not needed.
  const bool quality_converged =
      !layer_trackers_.empty() &&
      absl::c_all_of(layer_trackers_, [](const SpatialLayerTracker& tracker) {
        return tracker.quality_converged.value_or(true);
      });
  return quality_converged;
}

void ZeroHertzAdapterMode::ResetQualityConvergenceInfo() {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  RTC_DLOG(LS_INFO) << __func__ << " this " << this;
  for (auto& layer_tracker : layer_trackers_) {
    if (layer_tracker.quality_converged.has_value())
      layer_tracker.quality_converged = false;
  }
}

void ZeroHertzAdapterMode::ProcessOnDelayedCadence(Timestamp post_time) {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  RTC_DCHECK(!queued_frames_.empty());
  TRACE_EVENT0("webrtc", __func__);

  // Avoid sending the front frame for encoding (which could take a long time)
  // until we schedule a repeat.
  VideoFrame front_frame = queued_frames_.front();

  // If there were two or more frames stored, we do not have to schedule repeats
  // of the front frame.
  if (queued_frames_.size() > 1) {
    queued_frames_.pop_front();
  } else {
    // There's only one frame to send. Schedule a repeat sequence, which is
    // cancelled by `current_frame_id_` getting incremented should new frames
    // arrive.
    ScheduleRepeat(current_frame_id_, HasQualityConverged());
  }
  SendFrameNow(post_time, front_frame);
}

void ZeroHertzAdapterMode::ScheduleRepeat(int frame_id, bool idle_repeat) {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  Timestamp now = clock_->CurrentTime();
  if (!scheduled_repeat_.has_value()) {
    scheduled_repeat_.emplace(now, queued_frames_.front().timestamp_us(),
                              queued_frames_.front().ntp_time_ms());
  }
  scheduled_repeat_->scheduled = now;
  scheduled_repeat_->idle = idle_repeat;

  TimeDelta repeat_delay = RepeatDuration(idle_repeat);
  queue_->PostDelayedHighPrecisionTask(
      SafeTask(safety_.flag(),
               [this, frame_id] {
                 RTC_DCHECK_RUN_ON(&sequence_checker_);
                 ProcessRepeatedFrameOnDelayedCadence(frame_id);
               }),
      repeat_delay);
}

void ZeroHertzAdapterMode::ProcessRepeatedFrameOnDelayedCadence(int frame_id) {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  TRACE_EVENT0("webrtc", __func__);
  RTC_DCHECK(!queued_frames_.empty());

  // Cancel this invocation if new frames turned up.
  if (frame_id != current_frame_id_)
    return;
  RTC_DCHECK(scheduled_repeat_.has_value());

  VideoFrame& frame = queued_frames_.front();

  // Since this is a repeated frame, nothing changed compared to before.
  VideoFrame::UpdateRect empty_update_rect;
  empty_update_rect.MakeEmptyUpdate();
  frame.set_update_rect(empty_update_rect);

  // Adjust timestamps of the frame of the repeat, accounting for the actual
  // delay since we started repeating.
  //
  // NOTE: No need to update the RTP timestamp as the VideoStreamEncoder
  // overwrites it based on its chosen NTP timestamp source.
  TimeDelta total_delay = clock_->CurrentTime() - scheduled_repeat_->origin;
  if (frame.timestamp_us() > 0) {
    frame.set_timestamp_us(scheduled_repeat_->origin_timestamp_us +
                           total_delay.us());
  }
  if (frame.ntp_time_ms()) {
    frame.set_ntp_time_ms(scheduled_repeat_->origin_ntp_time_ms +
                          total_delay.ms());
  }

  // Schedule another repeat before sending the frame off which could take time.
  ScheduleRepeat(frame_id, HasQualityConverged());
  SendFrameNow(absl::nullopt, frame);
}

void ZeroHertzAdapterMode::SendFrameNow(absl::optional<Timestamp> post_time,
                                        const VideoFrame& frame) {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  TRACE_EVENT0("webrtc", __func__);

  Timestamp encode_start_time = clock_->CurrentTime();
  if (post_time.has_value()) {
    TimeDelta delay = (encode_start_time - *post_time);
    RTC_HISTOGRAM_COUNTS_10000("WebRTC.Screenshare.ZeroHz.DelayMs", delay.ms());
  }

  // Forward the frame and set `queue_overload` if is has been detected that it
  // is not possible to deliver frames at the expected rate due to slow
  // encoding.
  callback_->OnFrame(/*post_time=*/encode_start_time, queue_overload_count_ > 0,
                     frame);

  // WebRTC-ZeroHertzQueueOverload kill-switch.
  if (!zero_hertz_queue_overload_enabled_)
    return;

  // `queue_overload_count_` determines for how many future frames the
  // `queue_overload` flag will be set and it is only increased if:
  // o We are not already in an overload state.
  // o New frames have been scheduled for processing on the queue while encoding
  //   took place in OnFrame.
  // o The duration of OnFrame is longer than the current frame duration.
  // If all these conditions are fulfilled, `queue_overload_count_` is set to
  // `frames_scheduled_for_processing_` and any pending repeat is canceled since
  // new frames are available and the repeat is not needed.
  // If the adapter is already in an overload state, simply decrease
  // `queue_overload_count_` by one.
  if (queue_overload_count_ == 0) {
    const int frames_scheduled_for_processing =
        frames_scheduled_for_processing_.load(std::memory_order_relaxed);
    if (frames_scheduled_for_processing > 0) {
      TimeDelta encode_time = clock_->CurrentTime() - encode_start_time;
      if (encode_time > FrameDuration()) {
        queue_overload_count_ = frames_scheduled_for_processing;
        // Invalidates any outstanding repeat to avoid sending pending repeat
        // directly after too long encode.
        current_frame_id_++;
      }
    }
  } else {
    queue_overload_count_--;
  }
  RTC_HISTOGRAM_BOOLEAN("WebRTC.Screenshare.ZeroHz.QueueOverload",
                        queue_overload_count_ > 0);
}

TimeDelta ZeroHertzAdapterMode::FrameDuration() const {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  return std::max(frame_delay_, restricted_frame_delay_.value_or(frame_delay_));
}

TimeDelta ZeroHertzAdapterMode::RepeatDuration(bool idle_repeat) const {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  return idle_repeat
             ? FrameCadenceAdapterInterface::kZeroHertzIdleRepeatRatePeriod
             : FrameDuration();
}

void ZeroHertzAdapterMode::MaybeStartRefreshFrameRequester() {
  RTC_DCHECK_RUN_ON(&sequence_checker_);
  if (!refresh_frame_requester_.Running()) {
    refresh_frame_requester_ = RepeatingTaskHandle::DelayedStart(
        queue_,
        FrameCadenceAdapterInterface::kOnDiscardedFrameRefreshFramePeriod *
            frame_delay_,
        [this] {
          RTC_DLOG(LS_VERBOSE) << __func__ << " RequestRefreshFrame";
          if (callback_)
            callback_->RequestRefreshFrame();
          return frame_delay_;
        });
  }
}

void VSyncEncodeAdapterMode::OnFrame(Timestamp post_time,
                                     bool queue_overload,
                                     const VideoFrame& frame) {
  // We expect `metronome_` and `EncodeAllEnqueuedFrames()` runs on
  // `worker_queue_`.
  if (!worker_queue_->IsCurrent()) {
    worker_queue_->PostTask(SafeTask(
        worker_safety_.flag(), [this, post_time, queue_overload, frame] {
          OnFrame(post_time, queue_overload, frame);
        }));
    return;
  }

  RTC_DCHECK_RUN_ON(&worker_sequence_checker_);
  TRACE_EVENT0("webrtc", "VSyncEncodeAdapterMode::OnFrame");

  input_queue_.emplace_back(std::move(frame), post_time);

  // The `metronome_` tick period maybe throttled in some case, so here we only
  // align encode task to VSync event when `metronome_` tick period is less
  // than 34ms (30Hz).
  static constexpr TimeDelta kMaxAllowedDelay = TimeDelta::Millis(34);
  if (metronome_->TickPeriod() <= kMaxAllowedDelay) {
    // The metronome is ticking frequently enough that it is worth the extra
    // delay.
    metronome_->RequestCallOnNextTick(
        SafeTask(worker_safety_.flag(), [this] { EncodeAllEnqueuedFrames(); }));
  } else {
    // The metronome is ticking too infrequently, encode immediately.
    EncodeAllEnqueuedFrames();
  }
}

void VSyncEncodeAdapterMode::EncodeAllEnqueuedFrames() {
  RTC_DCHECK_RUN_ON(&worker_sequence_checker_);
  TRACE_EVENT0("webrtc", "VSyncEncodeAdapterMode::EncodeAllEnqueuedFrames");

  // Local time in webrtc time base.
  Timestamp post_time = clock_->CurrentTime();

  for (auto& input : input_queue_) {
    TRACE_EVENT1("webrtc", "FrameCadenceAdapterImpl::EncodeAllEnqueuedFrames",
                 "VSyncEncodeDelay",
                 (post_time - input.time_when_posted_us).ms());

    const VideoFrame frame = std::move(input.video_frame);
    MutexLock lock(&queue_lock_);
    if (queue_) {
      queue_->PostTask(SafeTask(queue_safety_flag_, [this, post_time, frame] {
        {
          MutexLock lock(&queue_lock_);
          if (!queue_) {
            return;
          }
          RTC_DCHECK_RUN_ON(queue_);
        }

        // TODO(b/304158952): Support more refined queue overload control.
        // Not running under mutex is safe since `callback_` existence is
        // guaranteed to exist as long as running encode queue tasks exist.
        callback_->OnFrame(post_time, /*queue_overload=*/false, frame);
      }));
    }
  }

  input_queue_.clear();
}

FrameCadenceAdapterImpl::FrameCadenceAdapterImpl(
    Clock* clock,
    TaskQueueBase* queue,
    Metronome* metronome,
    TaskQueueBase* worker_queue,
    const FieldTrialsView& field_trials)
    : clock_(clock),
      queue_(queue),
      frame_cadence_adapter_zero_hertz_queue_overload_enabled_(
          !field_trials.IsDisabled("WebRTC-ZeroHertzQueueOverload")),
      use_video_frame_timestamp_(field_trials.IsEnabled(
          "WebRTC-FrameCadenceAdapter-UseVideoFrameTimestamp")),
      metronome_(metronome),
      worker_queue_(worker_queue) {}

FrameCadenceAdapterImpl::~FrameCadenceAdapterImpl() {
  RTC_DLOG(LS_VERBOSE) << __func__ << " this " << this;

  // VSync adapter needs to be destroyed on worker queue when metronome is
  // valid.
  if (metronome_) {
    vsync_encode_adapter_->PrepareShutdown();
    absl::Cleanup cleanup = [adapter = std::move(vsync_encode_adapter_)] {};
    worker_queue_->PostTask([cleanup = std::move(cleanup)] {});
  }

  RTC_HISTOGRAM_BOOLEAN(
      "WebRTC.Video.InputFrameTimestampMonotonicallyIncreasing",
      incoming_frame_timestamp_monotonically_increasing_);
}

void FrameCadenceAdapterImpl::Initialize(Callback* callback) {
  callback_ = callback;
  // Use VSync encode mode if metronome is valid, otherwise passthrough mode
  // would be used.
  if (metronome_) {
    vsync_encode_adapter_ = std::make_unique<VSyncEncodeAdapterMode>(
        clock_, queue_, safety_.flag(), metronome_, worker_queue_, callback_);
  } else {
    passthrough_adapter_.emplace(callback);
  }
  ConfigureCurrentAdapterWithoutZeroHertz();
}

void FrameCadenceAdapterImpl::SetZeroHertzModeEnabled(
    absl::optional<ZeroHertzModeParams> params) {
  RTC_DCHECK_RUN_ON(queue_);
  bool was_zero_hertz_enabled = zero_hertz_params_.has_value();
  zero_hertz_params_ = params;
  MaybeReconfigureAdapters(was_zero_hertz_enabled);
}

absl::optional<uint32_t> FrameCadenceAdapterImpl::GetInputFrameRateFps() {
  RTC_DCHECK_RUN_ON(queue_);
  return current_adapter_mode_->GetInputFrameRateFps();
}

void FrameCadenceAdapterImpl::UpdateFrameRate(Timestamp frame_timestamp) {
  RTC_DCHECK_RUN_ON(queue_);
  // The frame rate need not be updated for the zero-hertz adapter. The
  // vsync encode and passthrough adapter however uses it. Always pass frames
  // into the vsync encode or passthrough to keep the estimation alive should
  // there be an adapter switch.
  if (metronome_) {
    RTC_CHECK(vsync_encode_adapter_);
    vsync_encode_adapter_->UpdateFrameRate(frame_timestamp);
  } else {
    RTC_CHECK(passthrough_adapter_);
    passthrough_adapter_->UpdateFrameRate(frame_timestamp);
  }
}

void FrameCadenceAdapterImpl::UpdateLayerQualityConvergence(
    size_t spatial_index,
    bool quality_converged) {
  if (zero_hertz_adapter_.has_value())
    zero_hertz_adapter_->UpdateLayerQualityConvergence(spatial_index,
                                                       quality_converged);
}

void FrameCadenceAdapterImpl::UpdateLayerStatus(size_t spatial_index,
                                                bool enabled) {
  if (zero_hertz_adapter_.has_value())
    zero_hertz_adapter_->UpdateLayerStatus(spatial_index, enabled);
}

void FrameCadenceAdapterImpl::UpdateVideoSourceRestrictions(
    absl::optional<double> max_frame_rate) {
  RTC_DCHECK_RUN_ON(queue_);
  // Store the restriction to ensure that it can be reapplied in possible
  // future adapter creations on configuration changes.
  restricted_max_frame_rate_ = max_frame_rate;
  if (zero_hertz_adapter_) {
    zero_hertz_adapter_->UpdateVideoSourceRestrictions(max_frame_rate);
  }
}

void FrameCadenceAdapterImpl::ProcessKeyFrameRequest() {
  RTC_DCHECK_RUN_ON(queue_);
  if (zero_hertz_adapter_)
    zero_hertz_adapter_->ProcessKeyFrameRequest();
}

void FrameCadenceAdapterImpl::OnFrame(const VideoFrame& frame) {
  // This method is called on the network thread under Chromium, or other
  // various contexts in test.
  RTC_DCHECK_RUNS_SERIALIZED(&incoming_frame_race_checker_);
  TRACE_EVENT0("webrtc", "FrameCadenceAdapterImpl::OnFrame");

  // Local time in webrtc time base.
  Timestamp post_time = clock_->CurrentTime();
  frames_scheduled_for_processing_.fetch_add(1, std::memory_order_relaxed);
  queue_->PostTask(SafeTask(safety_.flag(), [this, post_time, frame] {
    RTC_DCHECK_RUN_ON(queue_);
    if (zero_hertz_adapter_created_timestamp_.has_value()) {
      TimeDelta time_until_first_frame =
          clock_->CurrentTime() - *zero_hertz_adapter_created_timestamp_;
      zero_hertz_adapter_created_timestamp_ = absl::nullopt;
      RTC_HISTOGRAM_COUNTS_10000(
          "WebRTC.Screenshare.ZeroHz.TimeUntilFirstFrameMs",
          time_until_first_frame.ms());
    }

    const int frames_scheduled_for_processing =
        frames_scheduled_for_processing_.fetch_sub(1,
                                                   std::memory_order_relaxed);
    OnFrameOnMainQueue(post_time, frames_scheduled_for_processing > 1,
                       std::move(frame));
  }));
}

void FrameCadenceAdapterImpl::OnDiscardedFrame() {
  callback_->OnDiscardedFrame();
  queue_->PostTask(SafeTask(safety_.flag(), [this] {
    RTC_DCHECK_RUN_ON(queue_);
    if (zero_hertz_adapter_) {
      zero_hertz_adapter_->OnDiscardedFrame();
    }
  }));
}

void FrameCadenceAdapterImpl::OnConstraintsChanged(
    const VideoTrackSourceConstraints& constraints) {
  RTC_LOG(LS_INFO) << __func__ << " this " << this << " min_fps "
                   << constraints.min_fps.value_or(-1) << " max_fps "
                   << constraints.max_fps.value_or(-1);
  queue_->PostTask(SafeTask(safety_.flag(), [this, constraints] {
    RTC_DCHECK_RUN_ON(queue_);
    bool was_zero_hertz_enabled = IsZeroHertzScreenshareEnabled();
    source_constraints_ = constraints;
    MaybeReconfigureAdapters(was_zero_hertz_enabled);
  }));
}

void FrameCadenceAdapterImpl::OnFrameOnMainQueue(Timestamp post_time,
                                                 bool queue_overload,
                                                 const VideoFrame& frame) {
  RTC_DCHECK_RUN_ON(queue_);
  current_adapter_mode_->OnFrame(post_time, queue_overload, frame);
  if (last_incoming_frame_timestamp_ &&
      last_incoming_frame_timestamp_ >=
          Timestamp::Micros(frame.timestamp_us())) {
    RTC_LOG(LS_ERROR)
        << "Incoming frame timestamp is not monotonically increasing"
        << " current: " << frame.timestamp_us()
        << " last: " << last_incoming_frame_timestamp_.value().us();
    incoming_frame_timestamp_monotonically_increasing_ = false;
  }
  last_incoming_frame_timestamp_ = Timestamp::Micros(frame.timestamp_us());
  Timestamp update_frame_rate_timestamp =
      use_video_frame_timestamp_ ? *last_incoming_frame_timestamp_ : post_time;
  UpdateFrameRate(update_frame_rate_timestamp);
}

bool FrameCadenceAdapterImpl::IsZeroHertzScreenshareEnabled() const {
  RTC_DCHECK_RUN_ON(queue_);
  return source_constraints_.has_value() &&
         source_constraints_->max_fps.value_or(-1) > 0 &&
         source_constraints_->min_fps.value_or(-1) == 0 &&
         zero_hertz_params_.has_value();
}

void FrameCadenceAdapterImpl::ConfigureCurrentAdapterWithoutZeroHertz() {
  // Enable VSyncEncodeAdapterMode if metronome is valid.
  if (metronome_) {
    RTC_CHECK(vsync_encode_adapter_);
    current_adapter_mode_ = vsync_encode_adapter_.get();
  } else {
    RTC_CHECK(passthrough_adapter_);
    current_adapter_mode_ = &passthrough_adapter_.value();
  }
}

void FrameCadenceAdapterImpl::MaybeReconfigureAdapters(
    bool was_zero_hertz_enabled) {
  RTC_DCHECK_RUN_ON(queue_);
  bool is_zero_hertz_enabled = IsZeroHertzScreenshareEnabled();
  if (is_zero_hertz_enabled) {
    bool max_fps_has_changed = GetInputFrameRateFps().value_or(-1) !=
                               source_constraints_->max_fps.value_or(-1);
    if (!was_zero_hertz_enabled || max_fps_has_changed) {
      RTC_LOG(LS_INFO) << "Zero hertz mode enabled (max_fps="
                       << source_constraints_->max_fps.value() << ")";
      zero_hertz_adapter_.emplace(
          queue_, clock_, callback_, source_constraints_->max_fps.value(),
          frames_scheduled_for_processing_,
          frame_cadence_adapter_zero_hertz_queue_overload_enabled_);
      zero_hertz_adapter_->UpdateVideoSourceRestrictions(
          restricted_max_frame_rate_);
      zero_hertz_adapter_created_timestamp_ = clock_->CurrentTime();
    }
    zero_hertz_adapter_->ReconfigureParameters(zero_hertz_params_.value());
    current_adapter_mode_ = &zero_hertz_adapter_.value();
  } else {
    if (was_zero_hertz_enabled) {
      zero_hertz_adapter_ = absl::nullopt;
      RTC_LOG(LS_INFO) << "Zero hertz mode disabled.";
    }
    ConfigureCurrentAdapterWithoutZeroHertz();
  }
}

}  // namespace

std::unique_ptr<FrameCadenceAdapterInterface>
FrameCadenceAdapterInterface::Create(Clock* clock,
                                     TaskQueueBase* queue,
                                     Metronome* metronome,
                                     TaskQueueBase* worker_queue,
                                     const FieldTrialsView& field_trials) {
  return std::make_unique<FrameCadenceAdapterImpl>(clock, queue, metronome,
                                                   worker_queue, field_trials);
}

}  // namespace webrtc