decoder/renderer: no longer index automatically as part of the retrieve

functions

Indexing is a lengthy process and had a high chance of getting RenderWorkers
stuck doing it rather than being responsive to cache requests. This commit
introduces a system where workers never index media, but instead signal that
media is not ready to their RenderBackends which ensure that the media gets
indexed and re-queues the affected frames when those indexes are ready.

app/render/backend/renderbackend.h

@@ -31,7 +31,7 @@ public:
   void CancelQueue();
 
 public slots:
-  void InvalidateCache(const rational &start_range, const rational &end_range);
+  void InvalidateCache(const TimeRange &range);
 
   bool Compile();
 
@@ -145,6 +145,19 @@ private:
 
   RenderCancelDialog* cancel_dialog_;
 
+  struct FootageWaitInfo {
+    StreamPtr stream;
+    TimeRange affected_range;
+    rational stream_time;
+  };
+
+  QList<FootageWaitInfo> footage_wait_info_;
+
+private slots:
+  void FootageUnavailable(StreamPtr stream, Decoder::RetrieveState state, const TimeRange& path, const rational& stream_time);
+
+  void IndexUpdated(Stream *stream);
+
 };
 
 #endif // RENDERBACKEND_H