derive clips, tracks, and sequences from the same base

timeline/timelineobject.cpp

@@ -0,0 +1,29 @@
+#include "timelineobject.h"
+
+TimelineObject::TimelineObject()
+{  
+}
+
+TimelineObject::~TimelineObject()
+{
+}
+
+int TimelineObject::MediaWidth()
+{
+  return SequenceWidth();
+}
+
+int TimelineObject::MediaHeight()
+{
+  return SequenceHeight();
+}
+
+double TimelineObject::MediaFrameRate()
+{
+  return SequenceFrameRate();
+}
+
+NodeGraph *TimelineObject::pipeline()
+{
+  return &pipeline_;
+}