arranged items so they are inputs of folder rather than outputs

app/project/item/sequence/sequence.cpp

@@ -46,10 +46,9 @@ const QString Sequence::kTrackInputFormat = QStringLiteral("track_in_%1");
 
 const uint64_t Sequence::kVideoParamEditMask = VideoParamEdit::kWidthHeight | VideoParamEdit::kInterlacing | VideoParamEdit::kFrameRate | VideoParamEdit::kPixelAspect;
 
-#define super Item
+#define super Node
 
 Sequence::Sequence(bool viewer_only_mode) :
-  Item(!viewer_only_mode, true),
   video_frame_cache_(this),
   audio_playback_cache_(this),
   operation_stack_(0)
@@ -104,7 +103,7 @@ QIcon Sequence::icon() const
   return icon::Sequence;
 }
 
-QString Sequence::duration()
+QString Sequence::duration() const
 {
   rational timeline_length = GetLength();
 
@@ -113,7 +112,7 @@ QString Sequence::duration()
   return Timecode::timestamp_to_timecode(timestamp, video_params().time_base(), Core::instance()->GetTimecodeDisplay());
 }
 
-QString Sequence::rate()
+QString Sequence::rate() const
 {
   return tr("%1 FPS").arg(video_params().time_base().flipped().toDouble());
 }
@@ -341,7 +340,7 @@ void Sequence::InvalidateCache(const TimeRange& range, const QString& from, int
   super::InvalidateCache(range, from, element, job_time);
 }
 
-rational Sequence::GetLength()
+const rational& Sequence::GetLength() const
 {
   return last_length_;
 }

app/project/item/sequence/sequence.h

@@ -31,7 +31,6 @@
 #include "node/output/track/tracklist.h"
 #include "node/traverser.h"
 #include "project/item/footage/footage.h"
-#include "project/item/item.h"
 #include "render/audioparams.h"
 #include "render/audioplaybackcache.h"
 #include "render/framehashcache.h"
@@ -46,7 +45,7 @@ namespace olive {
 /**
  * @brief The main timeline object, an graph of edited clips that forms a complete edit
  */
-class Sequence : public Item, public TimelinePoints
+class Sequence : public Node, public TimelinePoints
 {
   Q_OBJECT
 public:
@@ -83,8 +82,8 @@ public:
 
   virtual QIcon icon() const override;
 
-  virtual QString duration() override;
-  virtual QString rate() override;
+  virtual QString duration() const override;
+  virtual QString rate() const override;
 
   void set_default_parameters();
 
@@ -136,7 +135,7 @@ public:
     SetStandardValue(kAudioParamsInput, QVariant::fromValue(audio));
   }
 
-  rational GetLength();
+  const rational &GetLength() const;
 
   virtual void Retranslate() override;
 
@@ -173,6 +172,11 @@ public:
     return uuid_;
   }
 
+  virtual bool IsItem() const override
+  {
+    return true;
+  }
+
 signals:
   void TimebaseChanged(const rational&);