viewer: allow queue some time to catch up

app/widget/viewer/viewer.cpp

@@ -95,7 +95,8 @@ ViewerWidget::ViewerWidget(QWidget *parent) :
   connect(display_widget_, &ViewerDisplayWidget::DragEntered, this, &ViewerWidget::DragEntered);
   connect(display_widget_, &ViewerDisplayWidget::Dropped, this, &ViewerWidget::Dropped);
   connect(display_widget_, &ViewerDisplayWidget::TextureChanged, this, &ViewerWidget::TextureChanged);
-  connect(display_widget_, &ViewerDisplayWidget::QueueStarved, this, &ViewerWidget::ForceRequeueFromCurrentTime);
+  connect(display_widget_, &ViewerDisplayWidget::QueueStarved, this, &ViewerWidget::QueueStarved);
+  connect(display_widget_, &ViewerDisplayWidget::QueueNoLongerStarved, this, &ViewerWidget::QueueNoLongerStarved);
   connect(display_widget_, &ViewerDisplayWidget::CreateAddableAt, this, &ViewerWidget::CreateAddableAt);
   connect(sizer_, &ViewerSizer::RequestScale, display_widget_, &ViewerDisplayWidget::SetMatrixZoom);
   connect(sizer_, &ViewerSizer::RequestTranslate, display_widget_, &ViewerDisplayWidget::SetMatrixTranslate);
@@ -636,6 +637,24 @@ void ViewerWidget::ReceivedAudioBufferForScrubbing()
   delete watcher;
 }
 
+void ViewerWidget::QueueStarved()
+{
+  static const int kMaximumWaitTime = 250;
+  qint64 now = QDateTime::currentMSecsSinceEpoch();
+
+  if (!queue_starved_start_) {
+    queue_starved_start_ = now;
+  } else if (now > queue_starved_start_ + kMaximumWaitTime) {
+    ForceRequeueFromCurrentTime();
+    queue_starved_start_ = 0;
+  }
+}
+
+void ViewerWidget::QueueNoLongerStarved()
+{
+  queue_starved_start_ = 0;
+}
+
 void ViewerWidget::ForceRequeueFromCurrentTime()
 {
   ClearVideoAutoCacherQueue();
@@ -732,6 +751,8 @@ void ViewerWidget::PlayInternal(int speed, bool in_to_out_only)
 
   controls_->ShowPauseButton();
 
+  queue_starved_start_ = 0;
+
   // Attempt to fill playback queue
   if (display_widget_->isVisible() || !windows_.isEmpty()) {
     prequeue_length_ = DeterminePlaybackQueueSize();

app/widget/viewer/viewer.h

@@ -274,6 +274,8 @@ private:
   Track::Reference recording_track_;
   QString recording_filename_;
 
+  qint64 queue_starved_start_;
+
 private slots:
   void PlaybackTimerUpdate();
 
@@ -321,6 +323,9 @@ private slots:
 
   void ReceivedAudioBufferForScrubbing();
 
+  void QueueStarved();
+  void QueueNoLongerStarved();
+
   void ForceRequeueFromCurrentTime();
 
   void UpdateAudioProcessor();

app/widget/viewer/viewerdisplay.cpp

@@ -67,7 +67,8 @@ ViewerDisplayWidget::ViewerDisplayWidget(QWidget *parent) :
   frames_skipped_(0),
   show_widget_background_(false),
   push_mode_(kPushNull),
-  add_band_(nullptr)
+  add_band_(nullptr),
+  queue_starved_(false)
 {
   connect(Core::instance(), &Core::ToolChanged, this, &ViewerDisplayWidget::ToolChanged);
 
@@ -894,6 +895,7 @@ void ViewerDisplayWidget::Pause()
   disconnect(this, &ViewerDisplayWidget::frameSwapped, this, &ViewerDisplayWidget::UpdateFromQueue);
 
   queue_.clear();
+  queue_starved_ = false;
 }
 
 void ViewerDisplayWidget::UpdateFromQueue()
@@ -905,6 +907,7 @@ void ViewerDisplayWidget::UpdateFromQueue()
   bool popped = false;
 
   if (queue_.empty()) {
+    queue_starved_ = true;
     emit QueueStarved();
   } else {
     while (!queue_.empty()) {
@@ -914,6 +917,11 @@ void ViewerDisplayWidget::UpdateFromQueue()
 
         // Frame was in queue, no need to decode anything
         SetImage(pf.frame);
+
+        if (queue_starved_) {
+          queue_starved_ = false;
+          emit QueueNoLongerStarved();
+        }
         return;
 
       } else if (pf.timestamp > time) {
@@ -936,6 +944,7 @@ void ViewerDisplayWidget::UpdateFromQueue()
         }
 
         if (queue_.empty()) {
+          queue_starved_ = true;
           emit QueueStarved();
           break;
         }

app/widget/viewer/viewerdisplay.h

@@ -212,6 +212,8 @@ signals:
 
   void QueueStarved();
 
+  void QueueNoLongerStarved();
+
   void CreateAddableAt(const QRectF &rect);
 
 protected:
@@ -384,6 +386,8 @@ private:
   QRubberBand *add_band_;
   QPoint add_band_start_;
 
+  bool queue_starved_;
+
 private slots:
   void EmitColorAtCursor(QMouseEvent* e);