Add watch time metrics for HTML5 media playback.

media/blink/watch_time_reporter.cc

Index: media/blink/watch_time_reporter.cc
diff --git a/media/blink/watch_time_reporter.cc b/media/blink/watch_time_reporter.cc
new file mode 100644
index 0000000000000000000000000000000000000000..73b9c877f2a6f5acd4241ddbacbcb6b484c3c010
--- /dev/null
+++ b/media/blink/watch_time_reporter.cc
@@ -0,0 +1,259 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/blink/watch_time_reporter.h"
+
+#include "base/power_monitor/power_monitor.h"
+
+namespace media {
+
+// The minimum amount of media playback which can elapse before we'll report
+// watch time metrics for a playback.
+constexpr base::TimeDelta kMinimumElapsedWatchTime =
+    base::TimeDelta::FromSeconds(7);
+
+// The minimum width and height of videos to report watch time metrics for.
+constexpr gfx::Size kMinimumVideoSize = gfx::Size(200, 200);
+
+const char WatchTimeReporter::kHistogramAudioVideoAll[] =
+    "Media.WatchTime.AudioVideo.All";
+const char WatchTimeReporter::kHistogramAudioVideoMse[] =
+    "Media.WatchTime.AudioVideo.MSE";
+const char WatchTimeReporter::kHistogramAudioVideoEme[] =
+    "Media.WatchTime.AudioVideo.EME";
+const char WatchTimeReporter::kHistogramAudioVideoSrc[] =
+    "Media.WatchTime.AudioVideo.SRC";
+const char WatchTimeReporter::kHistogramAudioVideoBattery[] =
+    "Media.WatchTime.AudioVideo.Battery";
+const char WatchTimeReporter::kHistogramAudioVideoAc[] =
+    "Media.WatchTime.AudioVideo.AC";
+
+WatchTimeReporter::WatchTimeReporter(bool has_audio,
+                                     bool has_video,
+                                     bool is_mse,
+                                     bool is_encrypted,
+                                     scoped_refptr<MediaLog> media_log,
+                                     const gfx::Size& initial_video_size,
+                                     const GetMediaTimeCB& get_media_time_cb)
+    : has_audio_(has_audio),
+      has_video_(has_video),
+      is_mse_(is_mse),
+      is_encrypted_(is_encrypted),
+      media_log_(std::move(media_log)),
+      initial_video_size_(initial_video_size),
+      get_media_time_cb_(get_media_time_cb) {
+  DCHECK(!get_media_time_cb_.is_null());
+  DCHECK(has_audio_ || has_video_);
+  if (has_video_)
+    DCHECK(!initial_video_size_.IsEmpty());
+  base::PowerMonitor::Get()->AddObserver(this);
+}
+
+WatchTimeReporter::~WatchTimeReporter() {
+  // If the timer is still running, finalize immediately, this is our last
+  // chance to capture metrics.
+  if (reporting_timer_.IsRunning())
+    MaybeFinalizeWatchTime(FinalizeTime::IMMEDIATELY);
+
+  base::PowerMonitor::Get()->RemoveObserver(this);
+}
+
+void WatchTimeReporter::OnPlaying() {
+  is_playing_ = true;
+  MaybeStartReportingTimer(get_media_time_cb_.Run());
+}
+
+void WatchTimeReporter::OnPaused() {
+  is_playing_ = false;
+  MaybeFinalizeWatchTime(FinalizeTime::ON_NEXT_UPDATE);
+}
+
+void WatchTimeReporter::OnSeeking() {
+  if (!reporting_timer_.IsRunning())
+    return;
+
+  // Seek is a special case that does not have hysteresis, when this is called
+  // the seek is imminent, so finalize the previous playback immediately.
+
+  // Don't trample an existing end timestamp.
+  if (end_timestamp_ != kNoTimestamp)
+    end_timestamp_ = get_media_time_cb_.Run();
+  UpdateWatchTime();
+}
+
+void WatchTimeReporter::OnVolumeChange(double volume) {
+  const double old_volume = volume_;
+  volume_ = volume;
+
+  // We're only interesting in transitions in and out of the muted state.
+  if (!old_volume && volume)
+    MaybeStartReportingTimer(get_media_time_cb_.Run());
+  else if (old_volume && !volume_)
+    MaybeFinalizeWatchTime(FinalizeTime::ON_NEXT_UPDATE);
+}
+
+void WatchTimeReporter::OnShown() {
+  is_visible_ = true;
+  MaybeStartReportingTimer(get_media_time_cb_.Run());
+}
+
+void WatchTimeReporter::OnHidden() {
+  is_visible_ = false;
+  MaybeFinalizeWatchTime(FinalizeTime::ON_NEXT_UPDATE);
+}
+
+void WatchTimeReporter::OnPowerStateChange(bool on_battery_power) {
+  if (!reporting_timer_.IsRunning())
+    return;
+
+  // Defer changing |is_on_battery_power_| until the next watch time report to
+  // avoid momentary power changes from affecting the results.
+  if (is_on_battery_power_ != on_battery_power) {
+    end_timestamp_for_power_ = get_media_time_cb_.Run();
+
+    // Restart the reporting timer so the full hysteresis is afforded.
+    reporting_timer_.Start(FROM_HERE, reporting_interval_, this,
+                           &WatchTimeReporter::UpdateWatchTime);
+    return;
+  }
+
+  end_timestamp_for_power_ = kNoTimestamp;
+}
+
+bool WatchTimeReporter::ShouldReportWatchTime() {
+  // Only report watch time for media of sufficient size with both audio and
+  // video tracks present.
+  return has_audio_ && has_video_ &&
+         initial_video_size_.height() >= kMinimumVideoSize.height() &&
+         initial_video_size_.width() >= kMinimumVideoSize.width();
+}
+
+void WatchTimeReporter::MaybeStartReportingTimer(
+    base::TimeDelta start_timestamp) {
+  // Don't start the timer if any of our state indicates we shouldn't; this
+  // check is important since the various event handlers do not have to care
+  // about the state of other events.
+  if (!ShouldReportWatchTime() || !is_playing_ || !volume_ || !is_visible_) {
+    // If we reach this point the timer should already have been stopped or
+    // there is a pending finalize in flight.
+    DCHECK(!reporting_timer_.IsRunning() || end_timestamp_ != kNoTimestamp);
+    return;
+  }
+
+  // If we haven't finalized the last watch time metrics yet, count this
+  // playback as a continuation of the previous metrics.
+  if (end_timestamp_ != kNoTimestamp) {
+    DCHECK(reporting_timer_.IsRunning());
+    end_timestamp_ = kNoTimestamp;
+    return;
+  }
+
+  // Don't restart the timer if it's already running.
+  if (reporting_timer_.IsRunning())
+    return;
+
+  last_media_timestamp_ = end_timestamp_for_power_ = kNoTimestamp;
+  is_on_battery_power_ = base::PowerMonitor::Get()->IsOnBatteryPower();
+  start_timestamp_ = start_timestamp_for_power_ = start_timestamp;
+  reporting_timer_.Start(FROM_HERE, reporting_interval_, this,
+                         &WatchTimeReporter::UpdateWatchTime);
+}
+
+void WatchTimeReporter::MaybeFinalizeWatchTime(FinalizeTime finalize_time) {
+  // Don't finalize if the timer is already stopped.
+  if (!reporting_timer_.IsRunning())
+    return;
+
+  // Don't trample an existing finalize; the first takes precedence.
+  if (end_timestamp_ == kNoTimestamp)
+    end_timestamp_ = get_media_time_cb_.Run();
+
+  if (finalize_time == FinalizeTime::IMMEDIATELY) {
+    UpdateWatchTime();
+    return;
+  }
+
+  // Always restart the timer when finalizing, so that we allow for the full
+  // length of |kReportingInterval| to elapse for hysteresis purposes.
+  DCHECK_EQ(finalize_time, FinalizeTime::ON_NEXT_UPDATE);
+  reporting_timer_.Start(FROM_HERE, reporting_interval_, this,
+                         &WatchTimeReporter::UpdateWatchTime);
+}
+
+void WatchTimeReporter::UpdateWatchTime() {
+  DCHECK(ShouldReportWatchTime());
+
+  const bool is_finalizing = end_timestamp_ != kNoTimestamp;
+  const bool is_power_change_pending = end_timestamp_for_power_ != kNoTimestamp;
+
+  // If we're finalizing the log, use the media time value at the time of
+  // finalization.
+  const base::TimeDelta current_timestamp =
+      is_finalizing ? end_timestamp_ : get_media_time_cb_.Run();
+  const base::TimeDelta elapsed = current_timestamp - start_timestamp_;
+
+  // Only report watch time after some minimum amount has elapsed. Don't update
+  // watch time if media time hasn't changed since the last run; this may occur
+  // if a seek is taking some time to complete or the playback is stalled for
+  // some reason.
+  if (elapsed >= kMinimumElapsedWatchTime &&
+      last_media_timestamp_ != current_timestamp) {
+    last_media_timestamp_ = current_timestamp;
+
+    std::unique_ptr<MediaLogEvent> log_event =
+        media_log_->CreateEvent(MediaLogEvent::Type::WATCH_TIME_UPDATE);
+
+    log_event->params.SetDoubleWithoutPathExpansion(kHistogramAudioVideoAll,
+                                                    elapsed.InSecondsF());
+    if (is_mse_)
+      log_event->params.SetDoubleWithoutPathExpansion(kHistogramAudioVideoMse,
+                                                      elapsed.InSecondsF());
+    else
+      log_event->params.SetDoubleWithoutPathExpansion(kHistogramAudioVideoSrc,
+                                                      elapsed.InSecondsF());
+    if (is_encrypted_)
+      log_event->params.SetDoubleWithoutPathExpansion(kHistogramAudioVideoEme,
+                                                      elapsed.InSecondsF());
+
+    // Record watch time using the last known value for |is_on_battery_power_|;
+    // if there's a |pending_power_change_| use that to accurately finalize the
+    // last bits of time in the previous bucket.
+    const base::TimeDelta elapsed_power =
+        (is_power_change_pending ? end_timestamp_for_power_
+                                 : current_timestamp) -
+        start_timestamp_for_power_;
+
+    // Again, only update watch time if enough time has elapsed; we need to
+    // recheck the elapsed time here since the power source can change anytime.
+    if (elapsed_power >= kMinimumElapsedWatchTime) {
+      if (is_on_battery_power_) {
+        log_event->params.SetDoubleWithoutPathExpansion(
+            kHistogramAudioVideoBattery, elapsed_power.InSecondsF());
+      } else {
+        log_event->params.SetDoubleWithoutPathExpansion(
+            kHistogramAudioVideoAc, elapsed_power.InSecondsF());
+      }
+    }
+
+    DVLOG(2) << "Sending watch time update.";
+    media_log_->AddEvent(std::move(log_event));
+  }
+
+  if (is_power_change_pending) {
+    // Invert battery power status here instead of using the value returned by
+    // the PowerObserver since there may be a pending OnPowerStateChange().
+    is_on_battery_power_ = !is_on_battery_power_;
+
+    start_timestamp_for_power_ = end_timestamp_for_power_;
+    end_timestamp_for_power_ = kNoTimestamp;
+  }
+
+  // Stop the timer if this is supposed to be our last tick.
+  if (is_finalizing) {
+    end_timestamp_ = kNoTimestamp;
+    reporting_timer_.Stop();
+  }
+}
+
+}  // namespace media