allow concurrent decoders for different blocks

app/node/traverser.cpp

@@ -350,7 +350,9 @@ NodeValueTable NodeTraverser::GenerateBlockTable(const Track *track, const TimeR
   NodeValueTable table;
 
   if (active_block) {
+    block_stack_.push_back(active_block);
     table = GenerateTable(active_block, Track::TransformRangeForBlock(active_block, range), track);
+    block_stack_.pop_back();
   }
 
   return table;

app/node/traverser.h

@@ -151,6 +151,11 @@ protected:
 
   void ResolveJobs(NodeValue &value, const TimeRange &range);
 
+  Block *GetCurrentBlock() const
+  {
+    return block_stack_.empty() ? nullptr : block_stack_.back();
+  }
+
 private:
   void PreProcessRow(const TimeRange &range, NodeValueRow &row);
 
@@ -167,6 +172,8 @@ private:
   const Node *transform_now_;
   QTransform *transform_;
 
+  std::list<Block*> block_stack_;
+
 };
 
 }