[Chromecast] Log playback stall event.

chromecast/media/cma/pipeline/media_pipeline_impl.cc

Index: chromecast/media/cma/pipeline/media_pipeline_impl.cc
diff --git a/chromecast/media/cma/pipeline/media_pipeline_impl.cc b/chromecast/media/cma/pipeline/media_pipeline_impl.cc
index 68fcaa72e67c5834f50f1e1f40019f885e26603d..7f326364527291746de82f1c2ba054d412895bdd 100644
--- a/chromecast/media/cma/pipeline/media_pipeline_impl.cc
+++ b/chromecast/media/cma/pipeline/media_pipeline_impl.cc
@@ -51,6 +51,9 @@ const base::TimeDelta kTimeUpdateInterval(
 // kTimeUpdateInterval * kStatisticsUpdatePeriod.
 const int kStatisticsUpdatePeriod = 4;
 
+// Stall duration threshold that triggers a playback stall event.
+constexpr int kPlaybackStallEventThreshold = 2500;
+
 void LogEstimatedBitrate(int decoded_bytes,
                          base::TimeDelta elapsed_time,
                          const char* tag,
@@ -87,6 +90,8 @@ MediaPipelineImpl::MediaPipelineImpl()
       statistics_rolling_counter_(0),
       audio_bytes_for_bitrate_estimation_(0),
       video_bytes_for_bitrate_estimation_(0),
+      playback_stalled_(false),
+      playback_stalled_notification_sent_(false),
       weak_factory_(this) {
   CMALOG(kLogControl) << __FUNCTION__;
   weak_this_ = weak_factory_.GetWeakPtr();
@@ -423,6 +428,55 @@ void MediaPipelineImpl::OnBufferingNotification(bool is_buffering) {
   }
 }
 
+void MediaPipelineImpl::CheckForPlaybackStall(base::TimeDelta media_time,
+                                              base::TimeTicks current_stc) {

[kmackay, 2016/06/03 17:37:05]

what does 'stc' stand for?

[ejason, 2016/06/03 19:20:15]

System time clock. I simply re-used the existing nomenclature from
UpdateMediaTime() (line 528). I'm open to changing this if you want, I don't
feel strongly one way or the other. 

+  DCHECK(media_time != ::media::kNoTimestamp());
+
+  // A playback stall is defined as a scenario where the underlying media
+  // pipeline has unexpectedly stopped making forward progress. The pipeline is
+  // NOT stalled if:
+  //
+  // 1. Media time is progressing
+  // 2. The backend is paused
+  // 3. We are currently buffering (this is captured in a separate event)
+  if (media_time != last_media_time_ ||
+      backend_state_ != BACKEND_STATE_PLAYING ||
+      (buffering_controller_ && buffering_controller_->IsBuffering())) {
+    if (playback_stalled_) {
+      // Transition out of the stalled condition.
+      base::TimeDelta stall_duration = current_stc - playback_stalled_time_;
+      CMALOG(kLogControl)
+          << "Transitioning out of stalled state. Stall duration was "
+          << stall_duration.InMilliseconds() << " ms";
+      playback_stalled_ = false;
+      playback_stalled_notification_sent_ = false;
+    }
+    return;
+  }
+
+  // Check to see if this is a new stall condition.
+  if (!playback_stalled_) {
+    playback_stalled_ = true;
+    playback_stalled_time_ = current_stc;
+    return;
+  }
+
+  // If we are in an existing stall, check to see if we've been stalled for more
+  // than 2.5 s. If so, send a single notification of the stall event.
+  if (!playback_stalled_notification_sent_) {
+    base::TimeDelta current_stall_duration =
+        current_stc - playback_stalled_time_;
+    if (current_stall_duration.InMilliseconds() >=
+        kPlaybackStallEventThreshold) {
+      CMALOG(kLogControl) << "Playback stalled";
+      metrics::CastMetricsHelper::GetInstance()->RecordApplicationEvent(
+          "Cast.Platform.PlaybackStall");
+      playback_stalled_notification_sent_ = true;
+    }
+    return;
+  }
+}
+
 void MediaPipelineImpl::UpdateMediaTime() {
   pending_time_update_task_ = false;
   if ((backend_state_ != BACKEND_STATE_PLAYING) &&
@@ -473,6 +527,8 @@ void MediaPipelineImpl::UpdateMediaTime() {
   }
   base::TimeTicks stc = base::TimeTicks::Now();
 
+  CheckForPlaybackStall(media_time, stc);
+
   base::TimeDelta max_rendering_time = media_time;
   if (buffering_controller_) {
     buffering_controller_->SetMediaTime(media_time);