render: queue audio alongside video

Previously, audio was all queued first and would therefore all have to
finish before any video frames could start caching. No longer! Now they're
queued side by side so users won't have to wait for audio to finish before
their cached frames come in.

app/render/backend/renderbackend.cpp

@@ -175,18 +175,19 @@ void RenderBackend::SetVideoDownloadMatrix(const QMatrix4x4 &mat)
   video_download_matrix_ = mat;
 }
 
-QList<TimeRange> RenderBackend::SplitRangeIntoChunks(const TimeRange &r)
+std::list<TimeRange> RenderBackend::SplitRangeIntoChunks(const TimeRange &r)
 {
+  // FIXME: Magic number
   const int chunk_size = 2;
 
-  QList<TimeRange> split_ranges;
+  std::list<TimeRange> split_ranges;
 
   int start_time = qFloor(r.in().toDouble() / static_cast<double>(chunk_size)) * chunk_size;
   int end_time = qCeil(r.out().toDouble() / static_cast<double>(chunk_size)) * chunk_size;
 
   for (int i=start_time; i<end_time; i+=chunk_size) {
-    split_ranges.append(TimeRange(qMax(r.in(), rational(i)),
-                                  qMin(r.out(), rational(i + chunk_size))));
+    split_ranges.push_back(TimeRange(qMax(r.in(), rational(i)),
+                                     qMin(r.out(), rational(i + chunk_size))));
   }
 
   return split_ranges;

app/render/backend/renderbackend.h

@@ -87,7 +87,7 @@ public:
 
   void SetVideoDownloadMatrix(const QMatrix4x4& mat);
 
-  static QList<TimeRange> SplitRangeIntoChunks(const TimeRange& r);
+  static std::list<TimeRange> SplitRangeIntoChunks(const TimeRange& r);
 
 public slots:
   void NodeGraphChanged(NodeInput *source);

app/task/render/render.cpp

@@ -74,16 +74,14 @@ void RenderTask::Render(const TimeRangeList& video_range,
   double total_length = 0;
   double video_frame_sz = video_params_.time_base().toDouble();
 
+  std::list<TimeRange> audio_queue;
   std::list<RangeSampleFuturePair> audio_lookup_table;
   if (!audio_range.isEmpty()) {
     foreach (const TimeRange& r, audio_range) {
       total_length += r.length().toDouble();
 
-      QList<TimeRange> ranges = RenderBackend::SplitRangeIntoChunks(r);
-
-      foreach (const TimeRange& split, ranges) {
-        audio_lookup_table.push_back({split, backend_.RenderAudio(split)});
-      }
+      std::list<TimeRange> ranges = RenderBackend::SplitRangeIntoChunks(r);
+      audio_queue.insert(audio_queue.end(), ranges.begin(), ranges.end());
     }
   }
 
@@ -123,6 +121,7 @@ void RenderTask::Render(const TimeRangeList& video_range,
   while (!IsCancelled()
          && (!render_lookup_table.empty()
              || !frame_queue.empty()
+             || !audio_queue.empty()
              || !download_futures.empty()
              || !audio_lookup_table.empty())) {
 
@@ -168,6 +167,11 @@ void RenderTask::Render(const TimeRangeList& video_range,
       frame_queue.pop_front();
     }
 
+    if (!audio_queue.empty()) {
+      audio_lookup_table.push_back({audio_queue.front(), backend_.RenderAudio(audio_queue.front())});
+      audio_queue.pop_front();
+    }
+
     i = render_lookup_table.begin();
 
     while (!IsCancelled() && i != render_lookup_table.end()) {