From 9d04a78f731b88887c3816d7dc00bb11356fc587 Mon Sep 17 00:00:00 2001
From: Markus Handell <handellm@webrtc.org>
Date: Thu, 12 May 2022 18:38:57 +0200
Subject: [PATCH] ZeroHertz: expose time to first frame statistic.

Bug: chromium:1324120
Change-Id: Ie609da309427ca5d2ff8585a8dc730586553c725
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/262247
Auto-Submit: Markus Handell <handellm@webrtc.org>
Commit-Queue: Markus Handell <handellm@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36867}
---
 video/BUILD.gn                          |  1 +
 video/frame_cadence_adapter.cc          | 16 ++++++++++++++++
 video/frame_cadence_adapter_unittest.cc | 16 ++++++++++++++++
 3 files changed, 33 insertions(+)

diff --git a/video/BUILD.gn b/video/BUILD.gn
index 51e846c677..71f4fc9742 100644
--- a/video/BUILD.gn
+++ b/video/BUILD.gn
@@ -305,6 +305,7 @@ rtc_library("frame_cadence_adapter") {
     "../api:sequence_checker",
     "../api/task_queue",
     "../api/units:time_delta",
+    "../api/units:timestamp",
     "../api/video:video_frame",
     "../rtc_base:checks",
     "../rtc_base:logging",
diff --git a/video/frame_cadence_adapter.cc b/video/frame_cadence_adapter.cc
index 7fc7939fdf..879cff71a1 100644
--- a/video/frame_cadence_adapter.cc
+++ b/video/frame_cadence_adapter.cc
@@ -21,6 +21,7 @@
 #include "api/sequence_checker.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"
@@ -184,6 +185,7 @@ class ZeroHertzAdapterMode : public AdapterMode {
   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_;
@@ -264,6 +266,10 @@ class FrameCadenceAdapterImpl : public FrameCadenceAdapterInterface {
   // Cache for the current adapter mode.
   AdapterMode* current_adapter_mode_ = nullptr;
 
+  // Timestamp for statistics reporting.
+  absl::optional<Timestamp> zero_hertz_adapter_created_timestamp_
+      RTC_GUARDED_BY(queue_);
+
   // Set up during Initialize.
   Callback* callback_ = nullptr;
 
@@ -619,6 +625,15 @@ void FrameCadenceAdapterImpl::OnFrame(const VideoFrame& frame) {
   frames_scheduled_for_processing_.fetch_add(1, std::memory_order_relaxed);
   queue_->PostTask(ToQueuedTask(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);
@@ -673,6 +688,7 @@ void FrameCadenceAdapterImpl::MaybeReconfigureAdapters(
         should_request_refresh_frame_ = false;
         callback_->RequestRefreshFrame();
       }
+      zero_hertz_adapter_created_timestamp_ = clock_->CurrentTime();
     }
     zero_hertz_adapter_->ReconfigureParameters(zero_hertz_params_.value());
     current_adapter_mode_ = &zero_hertz_adapter_.value();
diff --git a/video/frame_cadence_adapter_unittest.cc b/video/frame_cadence_adapter_unittest.cc
index 4770f051b7..823c1a2a6b 100644
--- a/video/frame_cadence_adapter_unittest.cc
+++ b/video/frame_cadence_adapter_unittest.cc
@@ -902,6 +902,22 @@ TEST_F(FrameCadenceAdapterMetricsTest, RecordsMinLtMaxConstraintIfSetOnFrame) {
       ElementsAre(Pair(60 * 4.0 + 5.0 - 1, 1)));
 }
 
+TEST_F(FrameCadenceAdapterMetricsTest, RecordsTimeUntilFirstFrame) {
+  MockCallback callback;
+  test::ScopedKeyValueConfig no_field_trials;
+  auto adapter = CreateAdapter(no_field_trials, time_controller_.GetClock());
+  adapter->Initialize(&callback);
+  adapter->SetZeroHertzModeEnabled(
+      FrameCadenceAdapterInterface::ZeroHertzModeParams{});
+  adapter->OnConstraintsChanged(VideoTrackSourceConstraints{0, 5.0});
+  time_controller_.AdvanceTime(TimeDelta::Millis(666));
+  adapter->OnFrame(CreateFrame());
+  DepleteTaskQueues();
+  EXPECT_THAT(
+      metrics::Samples("WebRTC.Screenshare.ZeroHz.TimeUntilFirstFrameMs"),
+      ElementsAre(Pair(666, 1)));
+}
+
 TEST(FrameCadenceAdapterRealTimeTest, TimestampsDoNotDrift) {
   // This regression test must be performed in realtime because of limitations
   // in GlobalSimulatedTimeController.