Reland "FrameCadenceAdapter: align video encoding to metronome"

This is a reland of commit b39c2a8464

Original change's description:
> FrameCadenceAdapter: align video encoding to metronome
>
> This CL aligns the video encoding tasks to metronome tick which
> similar with the metronome decoding.
>
> Design doc: https://docs.google.com/document/d/18PvEgS-DehClK6twCSCATOlX-j9acmXd-3vjb0tR9-Y
>
> Bug: b/304158952
> Change-Id: I262bd4a5097fdaeed559b9d7391a059ae86e2d63
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/327460
> Reviewed-by: Markus Handell <handellm@webrtc.org>
> Reviewed-by: Harald Alvestrand <hta@webrtc.org>
> Reviewed-by: Henrik Boström <hbos@webrtc.org>
> Commit-Queue: Zhaoliang Ma <zhaoliang.ma@intel.com>
> Cr-Commit-Position: refs/heads/main@{#41469}

Bug: b/304158952
Change-Id: Icf4e1ad91f5c98f3c32a88ffe4d6277e907353e6
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/333464
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Markus Handell <handellm@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#41479}

api/metronome/test/fake_metronome.cc

@@ -49,6 +49,10 @@ void ForcedTickMetronome::Tick() {
 FakeMetronome::FakeMetronome(TimeDelta tick_period)
     : tick_period_(tick_period) {}
 
+void FakeMetronome::SetTickPeriod(TimeDelta tick_period) {
+  tick_period_ = tick_period;
+}
+
 void FakeMetronome::RequestCallOnNextTick(
     absl::AnyInvocable<void() &&> callback) {
   TaskQueueBase* current = TaskQueueBase::Current();

api/metronome/test/fake_metronome.h

@@ -55,12 +55,14 @@ class FakeMetronome : public Metronome {
  public:
   explicit FakeMetronome(TimeDelta tick_period);
 
+  void SetTickPeriod(TimeDelta tick_period);
+
   // Metronome implementation.
   void RequestCallOnNextTick(absl::AnyInvocable<void() &&> callback) override;
   TimeDelta TickPeriod() const override;
 
  private:
-  const TimeDelta tick_period_;
+  TimeDelta tick_period_;
   std::vector<absl::AnyInvocable<void() &&>> callbacks_;
 };
 

api/peer_connection_interface.h

@@ -1442,6 +1442,10 @@ struct RTC_EXPORT PeerConnectionFactoryDependencies final {
       transport_controller_send_factory;
   // Metronome used for decoding, must be called on the worker thread.
   std::unique_ptr<Metronome> decode_metronome;
+  // Metronome used for encoding, must be called on the worker thread.
+  // TODO(b/304158952): Consider merging into a single metronome for all codec
+  // usage.
+  std::unique_ptr<Metronome> encode_metronome;
 
   // Media specific dependencies. Unused when `media_factory == nullptr`.
   rtc::scoped_refptr<AudioDeviceModule> adm;

call/call.cc

@@ -889,10 +889,11 @@ webrtc::VideoSendStream* Call::CreateVideoSendStream(
   VideoSendStream* send_stream = new VideoSendStream(
       &env_.clock(), num_cpu_cores_, &env_.task_queue_factory(),
       network_thread_, call_stats_->AsRtcpRttStats(), transport_send_.get(),
-      bitrate_allocator_.get(), video_send_delay_stats_.get(),
-      &env_.event_log(), std::move(config), std::move(encoder_config),
-      suspended_video_send_ssrcs_, suspended_video_payload_states_,
-      std::move(fec_controller), env_.field_trials());
+      config_.encode_metronome, bitrate_allocator_.get(),
+      video_send_delay_stats_.get(), &env_.event_log(), std::move(config),
+      std::move(encoder_config), suspended_video_send_ssrcs_,
+      suspended_video_payload_states_, std::move(fec_controller),
+      env_.field_trials());
 
   for (uint32_t ssrc : ssrcs) {
     RTC_DCHECK(video_send_ssrcs_.find(ssrc) == video_send_ssrcs_.end());

call/call_config.h

@@ -69,6 +69,7 @@ struct CallConfig {
       rtp_transport_controller_send_factory = nullptr;
 
   Metronome* decode_metronome = nullptr;
+  Metronome* encode_metronome = nullptr;
 
   // The burst interval of the pacer, see TaskQueuePacedSender constructor.
   absl::optional<TimeDelta> pacer_burst_interval;

pc/peer_connection_factory.cc

@@ -103,7 +103,8 @@ PeerConnectionFactory::PeerConnectionFactory(
           (dependencies->transport_controller_send_factory)
               ? std::move(dependencies->transport_controller_send_factory)
               : std::make_unique<RtpTransportControllerSendFactory>()),
-      decode_metronome_(std::move(dependencies->decode_metronome)) {}
+      decode_metronome_(std::move(dependencies->decode_metronome)),
+      encode_metronome_(std::move(dependencies->encode_metronome)) {}
 
 PeerConnectionFactory::PeerConnectionFactory(
     PeerConnectionFactoryDependencies dependencies)
@@ -119,6 +120,7 @@ PeerConnectionFactory::~PeerConnectionFactory() {
   worker_thread()->BlockingCall([this] {
     RTC_DCHECK_RUN_ON(worker_thread());
     decode_metronome_ = nullptr;
+    encode_metronome_ = nullptr;
   });
 }
 
@@ -344,6 +346,7 @@ std::unique_ptr<Call> PeerConnectionFactory::CreateCall_w(
   call_config.rtp_transport_controller_send_factory =
       transport_controller_send_factory_.get();
   call_config.decode_metronome = decode_metronome_.get();
+  call_config.encode_metronome = encode_metronome_.get();
   call_config.pacer_burst_interval = configuration.pacer_burst_interval;
   return context_->call_factory()->CreateCall(call_config);
 }

pc/peer_connection_factory.h

@@ -148,6 +148,7 @@ class PeerConnectionFactory : public PeerConnectionFactoryInterface {
   const std::unique_ptr<RtpTransportControllerSendFactoryInterface>
       transport_controller_send_factory_;
   std::unique_ptr<Metronome> decode_metronome_ RTC_GUARDED_BY(worker_thread());
+  std::unique_ptr<Metronome> encode_metronome_ RTC_GUARDED_BY(worker_thread());
 };
 
 }  // namespace webrtc

video/BUILD.gn

@@ -92,6 +92,7 @@ rtc_library("video") {
     "../api/crypto:frame_decryptor_interface",
     "../api/crypto:options",
     "../api/environment",
+    "../api/metronome",
     "../api/task_queue",
     "../api/task_queue:pending_task_safety_flag",
     "../api/units:data_rate",
@@ -230,6 +231,7 @@ rtc_library("frame_cadence_adapter") {
   deps = [
     "../api:field_trials_view",
     "../api:sequence_checker",
+    "../api/metronome",
     "../api/task_queue",
     "../api/task_queue:pending_task_safety_flag",
     "../api/units:time_delta",
@@ -253,6 +255,7 @@ rtc_library("frame_cadence_adapter") {
   absl_deps = [
     "//third_party/abseil-cpp/absl/algorithm:container",
     "//third_party/abseil-cpp/absl/base:core_headers",
+    "//third_party/abseil-cpp/absl/cleanup:cleanup",
   ]
 }
 

video/frame_cadence_adapter.cc

@@ -19,6 +19,7 @@
 
 #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"
@@ -234,10 +235,81 @@ class ZeroHertzAdapterMode : public AdapterMode {
   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();
+  }
+
+  // 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 input_framerate_.Rate(clock_->TimeInMilliseconds());
+  }
+
+  void UpdateFrameRate() override {
+    RTC_DCHECK_RUN_ON(&queue_sequence_checker_);
+    input_framerate_.Update(1, clock_->TimeInMilliseconds());
+  }
+
+  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_;
+  TaskQueueBase* queue_;
+  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.
+  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();
 
@@ -273,6 +345,10 @@ class FrameCadenceAdapterImpl : public FrameCadenceAdapterInterface {
   // - 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_);
 
@@ -283,14 +359,21 @@ class FrameCadenceAdapterImpl : public FrameCadenceAdapterInterface {
   // 0 Hz.
   const bool zero_hertz_screenshare_enabled_;
 
-  // The two possible modes we're under.
+  // 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_);
@@ -620,23 +703,98 @@ void ZeroHertzAdapterMode::MaybeStartRefreshFrameRequester() {
   }
 }
 
+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);
+    queue_->PostTask(SafeTask(queue_safety_flag_, [this, post_time, frame] {
+      RTC_DCHECK_RUN_ON(queue_);
+
+      // TODO(b/304158952): Support more refined queue overload control.
+      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),
       zero_hertz_screenshare_enabled_(
-          !field_trials.IsDisabled("WebRTC-ZeroHertzScreenshare")) {}
+          !field_trials.IsDisabled("WebRTC-ZeroHertzScreenshare")),
+      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_) {
+    absl::Cleanup cleanup = [adapter = std::move(vsync_encode_adapter_)] {};
+    worker_queue_->PostTask([cleanup = std::move(cleanup)] {});
+  }
 }
 
 void FrameCadenceAdapterImpl::Initialize(Callback* callback) {
   callback_ = callback;
-  passthrough_adapter_.emplace(clock_, callback);
-  current_adapter_mode_ = &passthrough_adapter_.value();
+  // 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(clock_, callback);
+  }
+  ConfigureCurrentAdapterWithoutZeroHertz();
 }
 
 void FrameCadenceAdapterImpl::SetZeroHertzModeEnabled(
@@ -655,9 +813,16 @@ absl::optional<uint32_t> FrameCadenceAdapterImpl::GetInputFrameRateFps() {
 void FrameCadenceAdapterImpl::UpdateFrameRate() {
   RTC_DCHECK_RUN_ON(queue_);
   // The frame rate need not be updated for the zero-hertz adapter. The
-  // passthrough adapter however uses it. Always pass frames into the
-  // passthrough to keep the estimation alive should there be an adapter switch.
-  passthrough_adapter_->UpdateFrameRate();
+  // 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();
+  } else {
+    RTC_CHECK(passthrough_adapter_);
+    passthrough_adapter_->UpdateFrameRate();
+  }
 }
 
 void FrameCadenceAdapterImpl::UpdateLayerQualityConvergence(
@@ -757,6 +922,17 @@ bool FrameCadenceAdapterImpl::IsZeroHertzScreenshareEnabled() const {
          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_);
@@ -780,7 +956,7 @@ void FrameCadenceAdapterImpl::MaybeReconfigureAdapters(
       zero_hertz_adapter_ = absl::nullopt;
       RTC_LOG(LS_INFO) << "Zero hertz mode disabled.";
     }
-    current_adapter_mode_ = &passthrough_adapter_.value();
+    ConfigureCurrentAdapterWithoutZeroHertz();
   }
 }
 
@@ -789,8 +965,11 @@ void FrameCadenceAdapterImpl::MaybeReconfigureAdapters(
 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, field_trials);
+  return std::make_unique<FrameCadenceAdapterImpl>(clock, queue, metronome,
+                                                   worker_queue, field_trials);
 }
 
 }  // namespace webrtc

video/frame_cadence_adapter.h

@@ -15,6 +15,7 @@
 
 #include "absl/base/attributes.h"
 #include "api/field_trials_view.h"
+#include "api/metronome/metronome.h"
 #include "api/task_queue/task_queue_base.h"
 #include "api/units/time_delta.h"
 #include "api/video/video_frame.h"
@@ -81,6 +82,8 @@ class FrameCadenceAdapterInterface
   static std::unique_ptr<FrameCadenceAdapterInterface> Create(
       Clock* clock,
       TaskQueueBase* queue,
+      Metronome* metronome,
+      TaskQueueBase* worker_queue,
       const FieldTrialsView& field_trials);
 
   // Call before using the rest of the API.

video/frame_cadence_adapter_unittest.cc

@@ -14,6 +14,7 @@
 #include <vector>
 
 #include "absl/functional/any_invocable.h"
+#include "api/metronome/test/fake_metronome.h"
 #include "api/task_queue/default_task_queue_factory.h"
 #include "api/task_queue/task_queue_base.h"
 #include "api/task_queue/task_queue_factory.h"
@@ -64,8 +65,9 @@ VideoFrame CreateFrameWithTimestamps(
 std::unique_ptr<FrameCadenceAdapterInterface> CreateAdapter(
     const FieldTrialsView& field_trials,
     Clock* clock) {
-  return FrameCadenceAdapterInterface::Create(clock, TaskQueueBase::Current(),
-                                              field_trials);
+  return FrameCadenceAdapterInterface::Create(
+      clock, TaskQueueBase::Current(), /*metronome=*/nullptr,
+      /*worker_queue=*/nullptr, field_trials);
 }
 
 class MockCallback : public FrameCadenceAdapterInterface::Callback {
@@ -593,7 +595,8 @@ TEST(FrameCadenceAdapterTest, IgnoresDropInducedCallbacksPostDestruction) {
   auto queue = time_controller.GetTaskQueueFactory()->CreateTaskQueue(
       "queue", TaskQueueFactory::Priority::NORMAL);
   auto adapter = FrameCadenceAdapterInterface::Create(
-      time_controller.GetClock(), queue.get(), enabler);
+      time_controller.GetClock(), queue.get(), /*metronome=*/nullptr,
+      /*worker_queue=*/nullptr, enabler);
   queue->PostTask([&adapter, &callback] {
     adapter->Initialize(callback.get());
     adapter->SetZeroHertzModeEnabled(
@@ -609,6 +612,82 @@ TEST(FrameCadenceAdapterTest, IgnoresDropInducedCallbacksPostDestruction) {
   time_controller.AdvanceTime(3 * TimeDelta::Seconds(1) / kMaxFps);
 }
 
+TEST(FrameCadenceAdapterTest, EncodeFramesAreAlignedWithMetronomeTick) {
+  ZeroHertzFieldTrialEnabler enabler;
+  GlobalSimulatedTimeController time_controller(Timestamp::Zero());
+  // Here the metronome interval is 33ms, because the metronome is not
+  // infrequent then the encode tasks are aligned with the tick period.
+  static constexpr TimeDelta kTickPeriod = TimeDelta::Millis(33);
+  auto queue = time_controller.GetTaskQueueFactory()->CreateTaskQueue(
+      "queue", TaskQueueFactory::Priority::NORMAL);
+  auto worker_queue = time_controller.GetTaskQueueFactory()->CreateTaskQueue(
+      "work_queue", TaskQueueFactory::Priority::NORMAL);
+  static test::FakeMetronome metronome(kTickPeriod);
+  auto adapter = FrameCadenceAdapterInterface::Create(
+      time_controller.GetClock(), queue.get(), &metronome, worker_queue.get(),
+      enabler);
+  MockCallback callback;
+  adapter->Initialize(&callback);
+  auto frame = CreateFrame();
+
+  // `callback->OnFrame()` would not be called if only 32ms went by after
+  // `adapter->OnFrame()`.
+  EXPECT_CALL(callback, OnFrame(_, false, _)).Times(0);
+  adapter->OnFrame(frame);
+  time_controller.AdvanceTime(TimeDelta::Millis(32));
+  Mock::VerifyAndClearExpectations(&callback);
+
+  // `callback->OnFrame()` should be called if 33ms went by after
+  // `adapter->OnFrame()`.
+  EXPECT_CALL(callback, OnFrame(_, false, _)).Times(1);
+  time_controller.AdvanceTime(TimeDelta::Millis(1));
+  Mock::VerifyAndClearExpectations(&callback);
+
+  // `callback->OnFrame()` would not be called if only 32ms went by after
+  // `adapter->OnFrame()`.
+  EXPECT_CALL(callback, OnFrame(_, false, _)).Times(0);
+  // Send two frame before next tick.
+  adapter->OnFrame(frame);
+  adapter->OnFrame(frame);
+  time_controller.AdvanceTime(TimeDelta::Millis(32));
+  Mock::VerifyAndClearExpectations(&callback);
+
+  // `callback->OnFrame()` should be called if 33ms went by after
+  // `adapter->OnFrame()`.
+  EXPECT_CALL(callback, OnFrame(_, false, _)).Times(2);
+  time_controller.AdvanceTime(TimeDelta::Millis(1));
+  Mock::VerifyAndClearExpectations(&callback);
+
+  // Change the metronome tick period to 67ms (15Hz).
+  metronome.SetTickPeriod(TimeDelta::Millis(67));
+  // Expect the encode would happen immediately.
+  EXPECT_CALL(callback, OnFrame(_, false, _)).Times(1);
+  adapter->OnFrame(frame);
+  time_controller.AdvanceTime(TimeDelta::Zero());
+  Mock::VerifyAndClearExpectations(&callback);
+
+  // Change the metronome tick period to 16ms (60Hz).
+  metronome.SetTickPeriod(TimeDelta::Millis(16));
+  // Expect the encode would not happen if only 15ms went by after
+  // `adapter->OnFrame()`.
+  EXPECT_CALL(callback, OnFrame(_, false, _)).Times(0);
+  adapter->OnFrame(frame);
+  time_controller.AdvanceTime(TimeDelta::Millis(15));
+  Mock::VerifyAndClearExpectations(&callback);
+  // `callback->OnFrame()` should be called if 16ms went by after
+  // `adapter->OnFrame()`.
+  EXPECT_CALL(callback, OnFrame(_, false, _)).Times(1);
+  time_controller.AdvanceTime(TimeDelta::Millis(1));
+  Mock::VerifyAndClearExpectations(&callback);
+
+  rtc::Event finalized;
+  queue->PostTask([&] {
+    adapter = nullptr;
+    finalized.Set();
+  });
+  finalized.Wait(rtc::Event::kForever);
+}
+
 class FrameCadenceAdapterSimulcastLayersParamTest
     : public ::testing::TestWithParam<int> {
  public:

video/video_send_stream.cc

@@ -114,6 +114,7 @@ std::unique_ptr<VideoStreamEncoder> CreateVideoStreamEncoder(
     VideoStreamEncoder::BitrateAllocationCallbackType
         bitrate_allocation_callback_type,
     const FieldTrialsView& field_trials,
+    Metronome* metronome,
     webrtc::VideoEncoderFactory::EncoderSelectorInterface* encoder_selector) {
   std::unique_ptr<TaskQueueBase, TaskQueueDeleter> encoder_queue =
       task_queue_factory->CreateTaskQueue("EncoderQueue",
@@ -122,8 +123,9 @@ std::unique_ptr<VideoStreamEncoder> CreateVideoStreamEncoder(
   return std::make_unique<VideoStreamEncoder>(
       clock, num_cpu_cores, stats_proxy, encoder_settings,
       std::make_unique<OveruseFrameDetector>(stats_proxy),
-      FrameCadenceAdapterInterface::Create(clock, encoder_queue_ptr,
-                                           field_trials),
+      FrameCadenceAdapterInterface::Create(
+          clock, encoder_queue_ptr, metronome,
+          /*worker_queue=*/TaskQueueBase::Current(), field_trials),
       std::move(encoder_queue), bitrate_allocation_callback_type, field_trials,
       encoder_selector);
 }
@@ -139,6 +141,7 @@ VideoSendStream::VideoSendStream(
     TaskQueueBase* network_queue,
     RtcpRttStats* call_stats,
     RtpTransportControllerSendInterface* transport,
+    Metronome* metronome,
     BitrateAllocatorInterface* bitrate_allocator,
     SendDelayStats* send_delay_stats,
     RtcEventLog* event_log,
@@ -161,6 +164,7 @@ VideoSendStream::VideoSendStream(
           config_.encoder_settings,
           GetBitrateAllocationCallbackType(config_, field_trials),
           field_trials,
+          metronome,
           config_.encoder_selector)),
       encoder_feedback_(
           clock,

video/video_send_stream.h

@@ -18,6 +18,7 @@
 
 #include "api/fec_controller.h"
 #include "api/field_trials_view.h"
+#include "api/metronome/metronome.h"
 #include "api/sequence_checker.h"
 #include "api/task_queue/pending_task_safety_flag.h"
 #include "call/bitrate_allocator.h"
@@ -62,6 +63,7 @@ class VideoSendStream : public webrtc::VideoSendStream {
       TaskQueueBase* network_queue,
       RtcpRttStats* call_stats,
       RtpTransportControllerSendInterface* transport,
+      Metronome* metronome,
       BitrateAllocatorInterface* bitrate_allocator,
       SendDelayStats* send_delay_stats,
       RtcEventLog* event_log,

video/video_stream_encoder_unittest.cc

@@ -875,8 +875,9 @@ class VideoStreamEncoderTest : public ::testing::Test {
         "EncoderQueue", TaskQueueFactory::Priority::NORMAL);
     TaskQueueBase* encoder_queue_ptr = encoder_queue.get();
     std::unique_ptr<FrameCadenceAdapterInterface> cadence_adapter =
-        FrameCadenceAdapterInterface::Create(time_controller_.GetClock(),
-                                             encoder_queue_ptr, field_trials_);
+        FrameCadenceAdapterInterface::Create(
+            time_controller_.GetClock(), encoder_queue_ptr,
+            /*metronome=*/nullptr, /*worker_queue=*/nullptr, field_trials_);
     video_stream_encoder_ = std::make_unique<VideoStreamEncoderUnderTest>(
         &time_controller_, std::move(cadence_adapter), std::move(encoder_queue),
         stats_proxy_.get(), video_send_config_.encoder_settings,
@@ -9556,7 +9557,7 @@ TEST(VideoStreamEncoderFrameCadenceTest,
       "WebRTC-ZeroHertzScreenshare/Enabled/");
   auto adapter = FrameCadenceAdapterInterface::Create(
       factory.GetTimeController()->GetClock(), encoder_queue.get(),
-      field_trials);
+      /*metronome=*/nullptr, /*worker_queue=*/nullptr, field_trials);
   FrameCadenceAdapterInterface* adapter_ptr = adapter.get();
 
   MockVideoSourceInterface mock_source;