(1) remove most uses of MementoCommand for Playlist and Region (2) move frozen state from Region into Stateful, renamed "suspend property changes" (3) successive changes to a Property (scalar) after clear_history() do not keep resetting the old value (fixes region trim)

git-svn-id: svn://localhost/ardour2/branches/3.0@6720 d708f5d6-7413-0410-9779-e7cbd77b26cf

35 files changed, 326 insertions, 362 deletions

diff --git a/gtk2_ardour/audio_region_editor.cc b/gtk2_ardour/audio_region_editor.cc
index e246c04391..adbb1e04ea 100644
--- a/gtk2_ardour/audio_region_editor.cc
+++ b/gtk2_ardour/audio_region_editor.cc
@@ -18,6 +18,7 @@
 */
 
 #include "pbd/memento_command.h"
+#include "pbd/stateful_diff_command.h"
 
 #include "ardour/session.h"
 #include "ardour/audioregion.h"
@@ -256,10 +257,9 @@ AudioRegionEditor::position_clock_changed ()
 	boost::shared_ptr<Playlist> pl = _region->playlist();
 
 	if (pl) {
-		XMLNode &before = pl->get_state();
+		_region->clear_history ();
 		_region->set_position (position_clock.current_time(), this);
-		XMLNode &after = pl->get_state();
-		_session->add_command(new MementoCommand<Playlist>(*pl, &before, &after));
+		_session->add_command(new StatefulDiffCommand (_region));
 	}
 
 	_session->commit_reversible_command ();
@@ -273,10 +273,9 @@ AudioRegionEditor::end_clock_changed ()
 	boost::shared_ptr<Playlist> pl = _region->playlist();
 
 	if (pl) {
-		XMLNode &before = pl->get_state();
+                _region->clear_history ();
 		_region->trim_end (end_clock.current_time(), this);
-		XMLNode &after = pl->get_state();
-		_session->add_command(new MementoCommand<Playlist>(*pl, &before, &after));
+		_session->add_command(new StatefulDiffCommand (_region));
 	}
 
 	_session->commit_reversible_command ();
@@ -294,10 +293,9 @@ AudioRegionEditor::length_clock_changed ()
 	boost::shared_ptr<Playlist> pl = _region->playlist();
 
 	if (pl) {
-		XMLNode &before = pl->get_state();
+                _region->clear_history ();
 		_region->trim_end (_region->position() + frames - 1, this);
-		XMLNode &after = pl->get_state();
-		_session->add_command(new MementoCommand<Playlist>(*pl, &before, &after));
+		_session->add_command(new StatefulDiffCommand (_region));
 	}
 
 	_session->commit_reversible_command ();
@@ -404,10 +402,9 @@ AudioRegionEditor::sync_offset_absolute_clock_changed ()
 {
 	_session->begin_reversible_command (_("change region sync point"));
 
-	XMLNode& before = _region->get_state ();
+        _region->clear_history ();
 	_region->set_sync_position (sync_offset_absolute_clock.current_time());
-	XMLNode& after = _region->get_state ();
-	_session->add_command (new MementoCommand<AudioRegion> (*_region.get(), &before, &after));
+	_session->add_command (new StatefulDiffCommand (_region));
 	
 	_session->commit_reversible_command ();
 }
@@ -417,10 +414,9 @@ AudioRegionEditor::sync_offset_relative_clock_changed ()
 {
 	_session->begin_reversible_command (_("change region sync point"));
 
-	XMLNode& before = _region->get_state ();
+        _region->clear_history ();
 	_region->set_sync_position (sync_offset_relative_clock.current_time() + _region->position ());
-	XMLNode& after = _region->get_state ();
-	_session->add_command (new MementoCommand<AudioRegion> (*_region.get(), &before, &after));
+	_session->add_command (new StatefulDiffCommand (_region));
 	
 	_session->commit_reversible_command ();
 }
diff --git a/gtk2_ardour/audio_region_view.cc b/gtk2_ardour/audio_region_view.cc
index 438867c9dc..7a0e76606e 100644
--- a/gtk2_ardour/audio_region_view.cc
+++ b/gtk2_ardour/audio_region_view.cc
@@ -267,8 +267,8 @@ AudioRegionView::audio_region() const
 void
 AudioRegionView::region_changed (const PropertyChange& what_changed)
 {
-	ENSURE_GUI_THREAD (*this, &AudioRegionView::region_changed, what_changed)
-	//cerr << "AudioRegionView::region_changed() called" << endl;
+	ENSURE_GUI_THREAD (*this, &AudioRegionView::region_changed, what_changed);
+        // cerr << "AudioRegionView::region_changed() called" << endl;
 
 	RegionView::region_changed (what_changed);
 
@@ -276,7 +276,7 @@ AudioRegionView::region_changed (const PropertyChange& what_changed)
 		region_scale_amplitude_changed ();
 	}
 	if (what_changed.contains (ARDOUR::Properties::fade_in)) {
-			fade_in_changed ();
+                fade_in_changed ();
 	}
 	if (what_changed.contains (ARDOUR::Properties::fade_out)) {
 		fade_out_changed ();
@@ -1022,6 +1022,10 @@ AudioRegionView::add_gain_point_event (ArdourCanvas::Item *item, GdkEvent *ev)
 
 	gain_line->view_to_model_coord (x, y);
 
+        /* XXX STATEFUL: can't convert to stateful diff until we 
+           can represent automation data with it.
+        */
+
 	trackview.session()->begin_reversible_command (_("add gain control point"));
 	XMLNode &before = audio_region()->envelope()->get_state();
 
diff --git a/gtk2_ardour/audio_streamview.cc b/gtk2_ardour/audio_streamview.cc
index 640120516c..ac95bf63c2 100644
--- a/gtk2_ardour/audio_streamview.cc
+++ b/gtk2_ardour/audio_streamview.cc
@@ -660,10 +660,10 @@ AudioStreamView::update_rec_regions ()
 
 					if (nlen != region->length()) {
 
-						region->freeze ();
+						region->suspend_property_changes ();
 						region->set_position (_trackview.get_diskstream()->get_capture_start_frame(n), this);
 						region->set_length (nlen, this);
-						region->thaw ();
+						region->resume_property_changes ();
 
 						if (origlen == 1) {
 							/* our special initial length */
@@ -685,10 +685,10 @@ AudioStreamView::update_rec_regions ()
 
 					if (region->source_length(0) >= region->start() + nlen) {
 
-						region->freeze ();
+						region->suspend_property_changes ();
 						region->set_position (_trackview.get_diskstream()->get_capture_start_frame(n), this);
 						region->set_length (nlen, this);
-						region->thaw ();
+						region->resume_property_changes ();
 
 						if (origlen == 1) {
 							/* our special initial length */
diff --git a/gtk2_ardour/editor_audio_import.cc b/gtk2_ardour/editor_audio_import.cc
index 05056f3829..201659d7b4 100644
--- a/gtk2_ardour/editor_audio_import.cc
+++ b/gtk2_ardour/editor_audio_import.cc
@@ -29,6 +29,7 @@
 #include "pbd/pthread_utils.h"
 #include "pbd/basename.h"
 #include "pbd/shortpath.h"
+#include "pbd/stateful_diff_command.h"
 
 #include <gtkmm2ext/choice.h>
 
@@ -840,9 +841,9 @@ Editor::finish_bringing_in_material (boost::shared_ptr<Region> region, uint32_t
 		boost::shared_ptr<Playlist> playlist = existing_track->diskstream()->playlist();
 		boost::shared_ptr<Region> copy (RegionFactory::create (region, region->properties()));
 		begin_reversible_command (_("insert file"));
-		XMLNode &before = playlist->get_state();
+                playlist->clear_history ();
 		playlist->add_region (copy, pos);
-		_session->add_command (new MementoCommand<Playlist>(*playlist, &before, &playlist->get_state()));
+		_session->add_command (new StatefulDiffCommand (playlist));
 		commit_reversible_command ();
 		break;
 	}
diff --git a/gtk2_ardour/editor_drag.cc b/gtk2_ardour/editor_drag.cc
index 2922ad19bb..cd6e5148f6 100644
--- a/gtk2_ardour/editor_drag.cc
+++ b/gtk2_ardour/editor_drag.cc
@@ -1425,9 +1425,9 @@ RegionInsertDrag::finished (GdkEvent* /*event*/, bool /*movement_occurred*/)
 	boost::shared_ptr<Playlist> playlist = dest_rtv->playlist();
 
 	_editor->begin_reversible_command (_("insert region"));
-	XMLNode& before = playlist->get_state ();
+        playlist->clear_history ();
 	playlist->add_region (_primary->region (), _last_frame_position);
-	_editor->session()->add_command (new MementoCommand<Playlist> (*playlist, &before, &playlist->get_state()));
+	_editor->session()->add_command (new StatefulDiffCommand (playlist));
 	_editor->commit_reversible_command ();
 
 	delete _primary;
@@ -1772,7 +1772,8 @@ TrimDrag::motion (GdkEvent* event, bool first_move)
 
 		for (list<RegionView*>::const_iterator i = _views.begin(); i != _views.end(); ++i) {
 			(*i)->fake_set_opaque(false);
-			(*i)->region()->freeze ();
+                        (*i)->region()->clear_history ();
+			(*i)->region()->suspend_property_changes ();
 
 			AudioRegionView* const arv = dynamic_cast<AudioRegionView*>(*i);
 
@@ -1784,7 +1785,6 @@ TrimDrag::motion (GdkEvent* event, bool first_move)
 			insert_result = _editor->motion_frozen_playlists.insert (pl);
 
 			if (insert_result.second) {
-				_editor->session()->add_command(new MementoCommand<Playlist>(*pl, &pl->get_state(), 0));
 				pl->freeze();
 			}
 		}
@@ -1867,13 +1867,13 @@ TrimDrag::finished (GdkEvent* event, bool movement_occurred)
 			for (list<RegionView*>::const_iterator i = _views.begin(); i != _views.end(); ++i) {
 				_editor->thaw_region_after_trim (**i);
 				(*i)->fake_set_opaque (true);
+                                if (_have_transaction) {
+                                        _editor->session()->add_command (new StatefulDiffCommand ((*i)->region()));
+                                }
 			}
 		}
 		for (set<boost::shared_ptr<Playlist> >::iterator p = _editor->motion_frozen_playlists.begin(); p != _editor->motion_frozen_playlists.end(); ++p) {
 			(*p)->thaw ();
-			if (_have_transaction) {
-				_editor->session()->add_command (new MementoCommand<Playlist>(*(*p).get(), 0, &(*p)->get_state()));
-			}
 		}
 
 		_editor->motion_frozen_playlists.clear ();
diff --git a/gtk2_ardour/editor_keyboard.cc b/gtk2_ardour/editor_keyboard.cc
index ea40b43f50..e6936232cd 100644
--- a/gtk2_ardour/editor_keyboard.cc
+++ b/gtk2_ardour/editor_keyboard.cc
@@ -17,13 +17,14 @@
 
 */
 
+#include "pbd/memento_command.h"
+#include "pbd/stateful_diff_command.h"
+
 #include "ardour/audioregion.h"
 #include "ardour/playlist.h"
 #include "ardour/session.h"
 #include "ardour/location.h"
 
-#include "pbd/memento_command.h"
-
 #include "editor.h"
 #include "region_view.h"
 #include "selection.h"
@@ -33,6 +34,7 @@
 #include "i18n.h"
 
 using namespace ARDOUR;
+using namespace PBD;
 
 void
 Editor::kbd_driver (sigc::slot<void,GdkEvent*> theslot, bool use_track_canvas, bool use_time_canvas, bool can_select)
@@ -89,11 +91,9 @@ Editor::kbd_mute_unmute_region ()
 
 		for (RegionSelection::iterator i = selection->regions.begin(); i != selection->regions.end(); ++i) {
 
-			XMLNode &before = (*i)->region()->playlist()->get_state ();
+			(*i)->region()->playlist()->clear_history ();
 			(*i)->region()->set_muted (!(*i)->region()->muted ());
-			XMLNode &after = (*i)->region()->playlist()->get_state ();
-
-			_session->add_command (new MementoCommand<ARDOUR::Playlist>(*((*i)->region()->playlist()), &before, &after));
+			_session->add_command (new StatefulDiffCommand ((*i)->region()->playlist()));
 
 		}
 
@@ -102,12 +102,9 @@ Editor::kbd_mute_unmute_region ()
 	} else if (entered_regionview) {
 
 		begin_reversible_command (_("mute region"));
-		XMLNode &before = entered_regionview->region()->playlist()->get_state();
-
+                entered_regionview->region()->playlist()->clear_history ();
 		entered_regionview->region()->set_muted (!entered_regionview->region()->muted());
-
-		XMLNode &after = entered_regionview->region()->playlist()->get_state();
-		_session->add_command (new MementoCommand<ARDOUR::Playlist>(*(entered_regionview->region()->playlist()), &before, &after));
+		_session->add_command (new StatefulDiffCommand (entered_regionview->region()->playlist()));
 		commit_reversible_command();
 
 	}
diff --git a/gtk2_ardour/editor_mouse.cc b/gtk2_ardour/editor_mouse.cc
index 5820218a2a..ee28ff6804 100644
--- a/gtk2_ardour/editor_mouse.cc
+++ b/gtk2_ardour/editor_mouse.cc
@@ -31,6 +31,7 @@
 #include <gtkmm2ext/tearoff.h>
 #include "pbd/memento_command.h"
 #include "pbd/basename.h"
+#include "pbd/stateful_diff_command.h"
 
 #include "ardour_ui.h"
 #include "actions.h"
@@ -2287,23 +2288,17 @@ Editor::point_trim (GdkEvent* event, nframes64_t new_bound)
 				}
 
 				if (!(*i)->region()->locked()) {
-					boost::shared_ptr<Playlist> pl = (*i)->region()->playlist();
-					XMLNode &before = pl->get_state();
-
+					(*i)->region()->clear_history ();
 					(*i)->region()->trim_front (new_bound, this);
-
-					XMLNode &after = pl->get_state();
-					_session->add_command(new MementoCommand<Playlist>(*pl.get(), &before, &after));
+					_session->add_command(new StatefulDiffCommand ((*i)->region()));
 				}
 			}
 
 		} else {
 			if (!rv->region()->locked()) {
-				boost::shared_ptr<Playlist> pl = rv->region()->playlist();
-				XMLNode &before = pl->get_state();
+				rv->region()->clear_history ();
 				rv->region()->trim_front (new_bound, this);
-				XMLNode &after = pl->get_state();
-				_session->add_command(new MementoCommand<Playlist>(*pl.get(), &before, &after));
+				_session->add_command(new StatefulDiffCommand (rv->region()));
 			}
 		}
 
@@ -2318,22 +2313,18 @@ Editor::point_trim (GdkEvent* event, nframes64_t new_bound)
 			for (list<RegionView*>::const_iterator i = selection->regions.by_layer().begin(); i != selection->regions.by_layer().end(); ++i)
 			{
 				if (!(*i)->region()->locked()) {
-					boost::shared_ptr<Playlist> pl = (*i)->region()->playlist();
-					XMLNode &before = pl->get_state();
+					(*i)->region()->clear_history();
 					(*i)->region()->trim_end (new_bound, this);
-					XMLNode &after = pl->get_state();
-					_session->add_command(new MementoCommand<Playlist>(*pl.get(), &before, &after));
+					_session->add_command(new StatefulDiffCommand ((*i)->region()));
 				}
 			}
 
 		} else {
 
 			if (!rv->region()->locked()) {
-				boost::shared_ptr<Playlist> pl = rv->region()->playlist();
-				XMLNode &before = pl->get_state();
+				rv->region()->clear_history ();
 				rv->region()->trim_end (new_bound, this);
-				XMLNode &after = pl->get_state();
-				_session->add_command (new MementoCommand<Playlist>(*pl.get(), &before, &after));
+				_session->add_command (new StatefulDiffCommand (rv->region()));
 			}
 		}
 
@@ -2354,7 +2345,7 @@ Editor::thaw_region_after_trim (RegionView& rv)
 		return;
 	}
 
-	region->thaw ();
+	region->resume_property_changes ();
 
 	AudioRegionView* arv = dynamic_cast<AudioRegionView*>(&rv);
 
@@ -2453,11 +2444,10 @@ Editor::mouse_brush_insert_region (RegionView* rv, nframes64_t pos)
 	boost::shared_ptr<Playlist> playlist = rtv->playlist();
 	double speed = rtv->get_diskstream()->speed();
 
-	XMLNode &before = playlist->get_state();
+        playlist->clear_history ();
 	boost::shared_ptr<Region> new_region (RegionFactory::create (rv->region()));
-	playlist->add_region (new_region, (nframes64_t) (pos * speed));
-	XMLNode &after = playlist->get_state();
-	_session->add_command(new MementoCommand<Playlist>(*playlist.get(), &before, &after));
+        playlist->add_region (new_region, (nframes64_t) (pos * speed));
+	_session->add_command (new StatefulDiffCommand (playlist));
 
 	// playlist is frozen, so we have to update manually XXX this is disgusting
 
@@ -2560,10 +2550,9 @@ Editor::start_selection_grab (ArdourCanvas::Item* /*item*/, GdkEvent* event)
 
 	boost::shared_ptr<Playlist> playlist = clicked_axisview->playlist();
 
-	XMLNode *before = &(playlist->get_state());
+        playlist->clear_history ();
 	clicked_routeview->playlist()->add_region (region, selection->time[clicked_selection].start);
-	XMLNode *after = &(playlist->get_state());
-	_session->add_command(new MementoCommand<Playlist>(*playlist, before, after));
+	_session->add_command(new StatefulDiffCommand (playlist));
 
 	commit_reversible_command ();
 
diff --git a/gtk2_ardour/editor_ops.cc b/gtk2_ardour/editor_ops.cc
index c3800b21fb..6eaf1fb41a 100644
--- a/gtk2_ardour/editor_ops.cc
+++ b/gtk2_ardour/editor_ops.cc
@@ -323,10 +323,9 @@ Editor::nudge_forward (bool next, bool force_playhead)
 				distance = next_distance;
 			}
 
-                        XMLNode &before = r->playlist()->get_state();
+                        r->clear_history ();
 			r->set_position (r->position() + distance, this);
-                        XMLNode &after = r->playlist()->get_state();
-			_session->add_command (new MementoCommand<Playlist>(*(r->playlist()), &before, &after));
+			_session->add_command (new StatefulDiffCommand (r));
 		}
 
 		commit_reversible_command ();
@@ -403,16 +402,15 @@ Editor::nudge_backward (bool next, bool force_playhead)
 			if (next) {
 				distance = next_distance;
 			}
-
-                        XMLNode &before = r->playlist()->get_state();
+                        
+                        r->clear_history ();
 
 			if (r->position() > distance) {
 				r->set_position (r->position() - distance, this);
 			} else {
 				r->set_position (0, this);
 			}
-                        XMLNode &after = r->playlist()->get_state();
-			_session->add_command(new MementoCommand<Playlist>(*(r->playlist()), &before, &after));
+			_session->add_command (new StatefulDiffCommand (r));
 		}
 
 		commit_reversible_command ();
@@ -493,10 +491,9 @@ Editor::nudge_forward_capture_offset ()
 		for (RegionSelection::iterator i = rs.begin(); i != rs.end(); ++i) {
 			boost::shared_ptr<Region> r ((*i)->region());
 
-			XMLNode &before = r->playlist()->get_state();
+                        r->clear_history ();
 			r->set_position (r->position() + distance, this);
-			XMLNode &after = r->playlist()->get_state();
-			_session->add_command(new MementoCommand<Playlist>(*(r->playlist()), &before, &after));
+			_session->add_command(new StatefulDiffCommand (r));
 		}
 
 		commit_reversible_command ();
@@ -523,15 +520,14 @@ Editor::nudge_backward_capture_offset ()
 		for (RegionSelection::iterator i = rs.begin(); i != rs.end(); ++i) {
 			boost::shared_ptr<Region> r ((*i)->region());
 
-                        XMLNode &before = r->playlist()->get_state();
+                        r->clear_history ();
 
 			if (r->position() > distance) {
 				r->set_position (r->position() - distance, this);
 			} else {
 				r->set_position (0, this);
 			}
-                        XMLNode &after = r->playlist()->get_state();
-			_session->add_command(new MementoCommand<Playlist>(*(r->playlist()), &before, &after));
+			_session->add_command(new StatefulDiffCommand (r));
 		}
 
 		commit_reversible_command ();
@@ -2225,9 +2221,9 @@ Editor::insert_region_list_drag (boost::shared_ptr<Region> region, int x, int y)
 	snap_to (where);
 
 	begin_reversible_command (_("insert dragged region"));
-        XMLNode &before = playlist->get_state();
+        playlist->clear_history ();
 	playlist->add_region (RegionFactory::create (region), where, 1.0);
-	_session->add_command(new MementoCommand<Playlist>(*playlist, &before, &playlist->get_state()));
+	_session->add_command(new StatefulDiffCommand (playlist));
 	commit_reversible_command ();
 }
 
@@ -2303,9 +2299,9 @@ Editor::insert_region_list_selection (float times)
 	}
 
 	begin_reversible_command (_("insert region"));
-	XMLNode &before = playlist->get_state();
+        playlist->clear_history ();
 	playlist->add_region ((RegionFactory::create (region)), get_preferred_edit_position(), times);
-	_session->add_command(new MementoCommand<Playlist>(*playlist, &before, &playlist->get_state()));
+	_session->add_command(new StatefulDiffCommand (playlist));
 	commit_reversible_command ();
 }
 
@@ -2818,11 +2814,7 @@ Editor::separate_regions_between (const TimeSelection& ts)
 
 				if ((playlist = rtv->playlist()) != 0) {
 
-					XMLNode *before;
-					bool got_some;
-
-					before = &(playlist->get_state());
-					got_some = false;
+					playlist->clear_history ();
 
 					/* XXX need to consider musical time selections here at some point */
 
@@ -2842,25 +2834,18 @@ Editor::separate_regions_between (const TimeSelection& ts)
 
 						if (!latest_regionviews.empty()) {
 
-							got_some = true;
-
 							rtv->view()->foreach_regionview (sigc::bind (
 										sigc::ptr_fun (add_if_covered),
 										&(*t), &new_selection));
-
+                                                        
 							if (!in_command) {
 								begin_reversible_command (_("separate"));
 								in_command = true;
 							}
 
-							_session->add_command(new MementoCommand<Playlist>(
-									*playlist, before, &playlist->get_state()));
+							_session->add_command(new StatefulDiffCommand (playlist));
 						}
 					}
-
-					if (!got_some) {
-						delete before;
-					}
 				}
 			}
 		}
@@ -3022,10 +3007,9 @@ Editor::crop_region_to (nframes64_t start, nframes64_t end)
 		the_end = min (end, the_end);
 		cnt = the_end - the_start + 1;
 
-		XMLNode &before = (*i)->get_state();
+                region->clear_history ();
 		region->trim_to (the_start, cnt, this);
-		XMLNode &after = (*i)->get_state();
-		_session->add_command (new MementoCommand<Playlist>(*(*i), &before, &after));
+		_session->add_command (new StatefulDiffCommand (region));
 	}
 
 	commit_reversible_command ();
@@ -3063,9 +3047,9 @@ Editor::region_fill_track ()
 			return;
 		}
 
-		XMLNode &before = pl->get_state();
+                pl->clear_history ();
 		pl->add_region (RegionFactory::create (region), region->last_frame(), times);
-		_session->add_command (new MementoCommand<Playlist>(*pl, &before, &pl->get_state()));
+		_session->add_command (new StatefulDiffCommand (pl));
 	}
 
 	commit_reversible_command ();
@@ -3107,9 +3091,9 @@ Editor::region_fill_selection ()
 			continue;
 		}
 
-                XMLNode &before = playlist->get_state();
+                playlist->clear_history ();
 		playlist->add_region (RegionFactory::create (region), start, times);
-		_session->add_command (new MementoCommand<Playlist>(*playlist, &before, &playlist->get_state()));
+		_session->add_command (new StatefulDiffCommand (playlist));
 	}
 
 	commit_reversible_command ();
@@ -3142,10 +3126,9 @@ Editor::set_sync_point (nframes64_t where, const RegionSelection& rs)
 			in_command = true;
 		}
 
-		XMLNode &before = region->playlist()->get_state();
+                region->clear_history ();
 		region->set_sync_position (where);
-		XMLNode &after = region->playlist()->get_state();
-		_session->add_command(new MementoCommand<Playlist>(*(region->playlist()), &before, &after));
+		_session->add_command(new StatefulDiffCommand (region));
 	}
 
 	if (in_command) {
@@ -3168,10 +3151,9 @@ Editor::remove_region_sync ()
 	begin_reversible_command (_("remove sync"));
 	for (RegionSelection::iterator i = rs.begin(); i != rs.end(); ++i) {
 
-                XMLNode &before = (*i)->region()->playlist()->get_state();
+                (*i)->region()->clear_history ();
 		(*i)->region()->clear_sync_position ();
-                XMLNode &after = (*i)->region()->playlist()->get_state();
-		_session->add_command(new MementoCommand<Playlist>(*((*i)->region()->playlist()), &before, &after));
+		_session->add_command(new StatefulDiffCommand ((*i)->region()));
 	}
 	commit_reversible_command ();
 }
@@ -3290,10 +3272,9 @@ Editor::align_selection_relative (RegionPoint point, nframes64_t position, const
 
 	/* move first one specially */
 
-	XMLNode &before = r->playlist()->get_state();
+        r->clear_history ();
 	r->set_position (pos, this);
-	XMLNode &after = r->playlist()->get_state();
-	_session->add_command(new MementoCommand<Playlist>(*(r->playlist()), &before, &after));
+	_session->add_command(new StatefulDiffCommand (r));
 
 	/* move rest by the same amount */
 
@@ -3303,16 +3284,15 @@ Editor::align_selection_relative (RegionPoint point, nframes64_t position, const
 
 		boost::shared_ptr<Region> region ((*i)->region());
 
-                XMLNode &before = region->playlist()->get_state();
+                region->clear_history ();
 
 		if (dir > 0) {
 			region->set_position (region->position() + distance, this);
 		} else {
 			region->set_position (region->position() - distance, this);
 		}
-
-                XMLNode &after = region->playlist()->get_state();
-		_session->add_command(new MementoCommand<Playlist>(*(region->playlist()), &before, &after));
+                
+		_session->add_command(new StatefulDiffCommand (region));
 
 	}
 
@@ -3346,7 +3326,7 @@ Editor::align_region (boost::shared_ptr<Region> region, RegionPoint point, nfram
 void
 Editor::align_region_internal (boost::shared_ptr<Region> region, RegionPoint point, nframes64_t position)
 {
-	XMLNode &before = region->playlist()->get_state();
+	region->clear_history ();
 
 	switch (point) {
 	case SyncPoint:
@@ -3364,8 +3344,7 @@ Editor::align_region_internal (boost::shared_ptr<Region> region, RegionPoint poi
 		break;
 	}
 
-	XMLNode &after = region->playlist()->get_state();
-	_session->add_command(new MementoCommand<Playlist>(*(region->playlist()), &before, &after));
+	_session->add_command(new StatefulDiffCommand (region));
 }
 
 void
@@ -3396,15 +3375,13 @@ Editor::trim_region (bool front)
 
 	for (list<RegionView*>::const_iterator i = rs.by_layer().begin(); i != rs.by_layer().end(); ++i) {
 		if (!(*i)->region()->locked()) {
-			boost::shared_ptr<Playlist> pl = (*i)->region()->playlist();
-			XMLNode &before = pl->get_state();
+                        (*i)->region()->clear_history ();
 			if (front) {
 				(*i)->region()->trim_front (where, this);
 			} else {
 				(*i)->region()->trim_end (where, this);
 			}
-			XMLNode &after = pl->get_state();
-			_session->add_command(new MementoCommand<Playlist>(*pl.get(), &before, &after));
+			_session->add_command (new StatefulDiffCommand ((*i)->region()));
 		}
 	}
 
@@ -3466,12 +3443,10 @@ Editor::trim_region_to_location (const Location& loc, const char* str)
 
 		start = session_frame_to_track_frame (loc.start(), speed);
 		end = session_frame_to_track_frame (loc.end(), speed);
-
-		XMLNode &before = rv->region()->playlist()->get_state();
+                
+		rv->region()->clear_history ();
 		rv->region()->trim_to (start, (end - start), this);
-		XMLNode &after = rv->region()->playlist()->get_state();
-		_session->add_command(new MementoCommand<Playlist>(
-				*(rv->region()->playlist()), &before, &after));
+		_session->add_command(new StatefulDiffCommand (rv->region()));
 	}
 
 	commit_reversible_command ();
@@ -3507,11 +3482,9 @@ Editor::trim_region_to_edit_point ()
 			speed = tav->get_diskstream()->speed();
 		}
 
-		XMLNode &before = rv->region()->playlist()->get_state();
+                rv->region()->clear_history ();
 		rv->region()->trim_end (session_frame_to_track_frame(where, speed), this);
-		XMLNode &after = rv->region()->playlist()->get_state();
-		_session->add_command(new MementoCommand<Playlist>(
-				*(rv->region()->playlist()), &before, &after));
+		_session->add_command(new StatefulDiffCommand (rv->region()));
 	}
 
 	commit_reversible_command ();
@@ -3547,11 +3520,9 @@ Editor::trim_region_from_edit_point ()
 			speed = tav->get_diskstream()->speed();
 		}
 
-		XMLNode &before = rv->region()->playlist()->get_state();
+                rv->region()->clear_history ();
 		rv->region()->trim_front (session_frame_to_track_frame(where, speed), this);
-		XMLNode &after = rv->region()->playlist()->get_state();
-		_session->add_command(new MementoCommand<Playlist>(
-				*(rv->region()->playlist()), &before, &after));
+		_session->add_command(new StatefulDiffCommand (rv->region()));
 	}
 
 	commit_reversible_command ();
@@ -3604,7 +3575,7 @@ Editor::trim_to_region(bool forward)
 		boost::shared_ptr<Region> region = arv->region();
 		boost::shared_ptr<Playlist> playlist (region->playlist());
 
-		XMLNode &before = playlist->get_state();
+                region->clear_history ();
 
 		if(forward){
 
@@ -3630,8 +3601,7 @@ Editor::trim_to_region(bool forward)
 		    arv->region_changed (ARDOUR::bounds_change);
 		}
 
-		XMLNode &after = playlist->get_state();
-		_session->add_command(new MementoCommand<Playlist>(*playlist, &before, &after));
+		_session->add_command(new StatefulDiffCommand (region));
 	}
 
 	commit_reversible_command ();
@@ -3658,7 +3628,7 @@ Editor::_freeze_thread (void* arg)
 void*
 Editor::freeze_thread ()
 {
-	clicked_routeview->audio_track()->freeze (*current_interthread_info);
+	clicked_routeview->audio_track()->freeze_me (*current_interthread_info);
 	current_interthread_info->done = true;
 	return 0;
 }
@@ -3747,7 +3717,7 @@ Editor::bounce_range_selection (bool replace, bool enable_processing)
 		itt.cancel = false;
 		itt.progress = false;
 
-                XMLNode &before = playlist->get_state();
+                playlist->clear_history ();
 		boost::shared_ptr<Region> r = rtv->track()->bounce_range (start, start+cnt, itt, enable_processing);
 
 		if (replace) {
@@ -3757,8 +3727,7 @@ Editor::bounce_range_selection (bool replace, bool enable_processing)
 			playlist->add_region (r, start);
 		}
 
-                XMLNode &after = playlist->get_state();
-		_session->add_command (new MementoCommand<Playlist> (*playlist, &before, &after));
+		_session->add_command (new StatefulDiffCommand (playlist));
 	}
 
 	commit_reversible_command ();
@@ -3994,10 +3963,9 @@ Editor::remove_clicked_region ()
 	boost::shared_ptr<Playlist> playlist = clicked_routeview->playlist();
 
 	begin_reversible_command (_("remove region"));
-        XMLNode &before = playlist->get_state();
+        playlist->clear_history ();
 	playlist->remove_region (clicked_regionview->region());
-        XMLNode &after = playlist->get_state();
-	_session->add_command(new MementoCommand<Playlist>(*playlist, &before, &after));
+	_session->add_command(new StatefulDiffCommand (playlist));
 	commit_reversible_command ();
 }
 
@@ -4034,7 +4002,7 @@ Editor::remove_selected_regions ()
 		regions_to_remove.push_back ((*i)->region());
 	}
 
-	vector<PlaylistState> playlists;
+        vector<boost::shared_ptr<Playlist> > playlists;
 
 	for (list<boost::shared_ptr<Region> >::iterator rl = regions_to_remove.begin(); rl != regions_to_remove.end(); ++rl) {
 
@@ -4045,33 +4013,31 @@ Editor::remove_selected_regions ()
 	        	continue;
 	        }
 
-		vector<PlaylistState>::iterator i;
+		vector<boost::shared_ptr<Playlist> >::iterator i;
 
-		//only take state if this is a new playlist.
+		//only prep history if this is a new playlist.
 		for (i = playlists.begin(); i != playlists.end(); ++i) {
-			if ((*i).playlist == playlist) {
+			if ((*i) == playlist) {
 				break;
 			}
 		}
 
 		if (i == playlists.end()) {
 
-			PlaylistState before;
-			before.playlist = playlist;
-			before.before = &playlist->get_state();
-
+                        playlist->clear_history ();
 			playlist->freeze ();
-			playlists.push_back(before);
+
+			playlists.push_back (playlist);
 		}
 
 		playlist->remove_region (*rl);
 	}
 
-	vector<PlaylistState>::iterator pl;
+	vector<boost::shared_ptr<Playlist> >::iterator pl;
 
 	for (pl = playlists.begin(); pl != playlists.end(); ++pl) {
-		(*pl).playlist->thaw ();
-		_session->add_command(new MementoCommand<Playlist>(*(*pl).playlist, (*pl).before, &(*pl).playlist->get_state()));
+		(*pl)->thaw ();
+		_session->add_command(new StatefulDiffCommand (*pl));
 	}
 
 	commit_reversible_command ();
@@ -4351,9 +4317,9 @@ Editor::duplicate_some_regions (RegionSelection& regions, float times)
 		sigc::connection c = rtv->view()->RegionViewAdded.connect (sigc::mem_fun(*this, &Editor::collect_new_region_view));
 
  		playlist = (*i)->region()->playlist();
-                XMLNode &before = playlist->get_state();
+                playlist->clear_history ();
 		playlist->duplicate (r, end_frame + (r->first_frame() - start_frame) + 1, times);
-		_session->add_command(new MementoCommand<Playlist>(*playlist, &before, &playlist->get_state()));
+		_session->add_command(new StatefulDiffCommand (playlist));
 
 		c.disconnect ();
 
@@ -4392,10 +4358,9 @@ Editor::duplicate_selection (float times)
 		if ((playlist = (*i)->playlist()) == 0) {
 			continue;
 		}
-		XMLNode &before = playlist->get_state();
+                playlist->clear_history ();
 		playlist->duplicate (*ri, selection->time[clicked_selection].end, times);
-		XMLNode &after = playlist->get_state();
-		_session->add_command (new MementoCommand<Playlist>(*playlist, &before, &after));
+		_session->add_command (new StatefulDiffCommand (playlist));
 
 		++ri;
 		if (ri == new_regions.end()) {
@@ -4439,10 +4404,9 @@ void
 Editor::clear_playlist (boost::shared_ptr<Playlist> playlist)
 {
 	begin_reversible_command (_("clear playlist"));
-        XMLNode &before = playlist->get_state();
+        playlist->clear_history ();
 	playlist->clear ();
-        XMLNode &after = playlist->get_state();
-	_session->add_command (new MementoCommand<Playlist>(*playlist.get(), &before, &after));
+	_session->add_command (new StatefulDiffCommand (playlist));
 	commit_reversible_command ();
 }
 
@@ -4476,6 +4440,9 @@ Editor::nudge_track (bool use_edit, bool forwards)
 			continue;
 		}
 
+                /* XXX STATEFUL this won't capture region moves if don't as a stateful diff
+                 */
+
                 XMLNode &before = playlist->get_state();
 		playlist->nudge_after (start, distance, forwards);
                 XMLNode &after = playlist->get_state();
@@ -4555,9 +4522,10 @@ Editor::normalize_region ()
 		AudioRegionView* const arv = dynamic_cast<AudioRegionView*>(*r);
 		if (!arv)
 			continue;
- 		XMLNode &before = arv->region()->get_state();
+                arv->region()->clear_history ();
 		arv->audio_region()->normalize_to (spin.get_value());
-		_session->add_command (new MementoCommand<Region>(*(arv->region().get()), &before, &arv->region()->get_state()));
+		_session->add_command (new StatefulDiffCommand (arv->region()));
+                                       
 	}
 
 	commit_reversible_command ();
@@ -4588,9 +4556,9 @@ Editor::reset_region_scale_amplitude ()
 		AudioRegionView* const arv = dynamic_cast<AudioRegionView*>(*r);
 		if (!arv)
 			continue;
-		XMLNode &before = arv->region()->get_state();
+                arv->region()->clear_history ();
 		arv->audio_region()->set_scale_amplitude (1.0f);
-		_session->add_command (new MementoCommand<Region>(*(arv->region().get()), &before, &arv->region()->get_state()));
+		_session->add_command (new StatefulDiffCommand (arv->region()));
 	}
 
 	commit_reversible_command ();
@@ -4615,10 +4583,12 @@ Editor::adjust_region_scale_amplitude (bool up)
 
 	for (RegionSelection::iterator r = rs.begin(); r != rs.end(); ++r) {
 		AudioRegionView* const arv = dynamic_cast<AudioRegionView*>(*r);
-		if (!arv)
+		if (!arv) {
 			continue;
-		XMLNode &before = arv->region()->get_state();
+                }
 
+                arv->region()->clear_history ();
+                
 		double fraction = gain_to_slider_position (arv->audio_region()->scale_amplitude ());
 
 		if (up) {
@@ -4640,7 +4610,7 @@ Editor::adjust_region_scale_amplitude (bool up)
 		}
 
 		arv->audio_region()->set_scale_amplitude (fraction);
-		_session->add_command (new MementoCommand<Region>(*(arv->region().get()), &before, &arv->region()->get_state()));
+		_session->add_command (new StatefulDiffCommand (arv->region()));
 	}
 
 	commit_reversible_command ();
@@ -4786,8 +4756,8 @@ Editor::apply_filter (Filter& filter, string command)
 
 			if (arv->audio_region()->apply (filter) == 0) {
 
-				XMLNode &before = playlist->get_state();
-
+				playlist->clear_history ();
+                                
 				if (filter.results.empty ()) {
 
 					/* no regions returned; remove the old one */
@@ -4809,8 +4779,7 @@ Editor::apply_filter (Filter& filter, string command)
 
 				}
 
-				XMLNode &after = playlist->get_state();
-				_session->add_command(new MementoCommand<Playlist>(*playlist, &before, &after));
+				_session->add_command(new StatefulDiffCommand (playlist));
 			} else {
 				goto out;
 			}
@@ -4918,10 +4887,9 @@ Editor::toggle_gain_envelope_visibility ()
 	for (RegionSelection::iterator i = rs.begin(); i != rs.end(); ++i) {
 		AudioRegionView* const arv = dynamic_cast<AudioRegionView*>(*i);
 		if (arv) {
-			XMLNode &before = arv->region()->get_state ();
+                        arv->region()->clear_history ();
 			arv->set_envelope_visible (!arv->envelope_visible());
-			XMLNode &after = arv->region()->get_state ();
-			_session->add_command (new MementoCommand<Region> (*(arv->region().get()), &before, &after));
+			_session->add_command (new StatefulDiffCommand (arv->region()));
 		}
 	}
 
@@ -4983,10 +4951,9 @@ Editor::set_region_lock_style (Region::PositionLockStyle ps)
 	_session->begin_reversible_command (_("region lock style"));
 
 	for (RegionSelection::iterator i = rs.begin(); i != rs.end(); ++i) {
-		XMLNode &before = (*i)->region()->get_state ();
+                (*i)->region()->clear_history ();
 		(*i)->region()->set_position_lock_style (ps);
-		XMLNode &after = (*i)->region()->get_state ();
-		_session->add_command (new MementoCommand<Region> (*((*i)->region().get()), &before, &after));
+		_session->add_command (new StatefulDiffCommand ((*i)->region()));
 	}
 
 	_session->commit_reversible_command ();
@@ -5165,14 +5132,15 @@ Editor::toggle_fade_active (bool in)
 			have_switch = true;
 		}
 
-		XMLNode &before = region->get_state();
+		region->clear_history ();
+
 		if (in) {
 			region->set_fade_in_active (!yn);
 		} else {
 			region->set_fade_out_active (!yn);
 		}
-		XMLNode &after = region->get_state();
-		_session->add_command(new MementoCommand<AudioRegion>(*region.get(), &before, &after));
+		
+		_session->add_command(new StatefulDiffCommand (region));
 	}
 
 	commit_reversible_command ();
@@ -5265,13 +5233,10 @@ Editor::set_fade_in_active (bool yn)
 
 
 		boost::shared_ptr<AudioRegion> ar (tmp->audio_region());
-
-		XMLNode &before = ar->get_state();
-
+		
+                ar->clear_history ();
 		ar->set_fade_in_active (yn);
-
-		XMLNode &after = ar->get_state();
-		_session->add_command(new MementoCommand<AudioRegion>(*ar, &before, &after));
+		_session->add_command (new StatefulDiffCommand (ar));
 	}
 
 	commit_reversible_command ();
@@ -5299,12 +5264,9 @@ Editor::set_fade_out_active (bool yn)
 
 		boost::shared_ptr<AudioRegion> ar (tmp->audio_region());
 
-		XMLNode &before = ar->get_state();
-
+                ar->clear_history ();
 		ar->set_fade_out_active (yn);
-
-		XMLNode &after = ar->get_state();
-		_session->add_command(new MementoCommand<AudioRegion>(*ar, &before, &after));
+		_session->add_command(new StatefulDiffCommand (ar));
 	}
 
 	commit_reversible_command ();
@@ -5925,7 +5887,7 @@ Editor::split_region_at_points (boost::shared_ptr<Region> r, AnalysisFeatureList
 
 	nframes64_t pos = r->position();
 
-	XMLNode& before (pl->get_state());
+        pl->clear_history ();
 
 	x = positions.begin();
 
@@ -6007,9 +5969,7 @@ Editor::split_region_at_points (boost::shared_ptr<Region> r, AnalysisFeatureList
 
 	pl->thaw ();
 
-	XMLNode& after (pl->get_state());
-
-	_session->add_command (new MementoCommand<Playlist>(*pl, &before, &after));
+	_session->add_command (new StatefulDiffCommand (pl));
 }
 
 void
@@ -6330,6 +6290,9 @@ Editor::insert_time (nframes64_t pos, nframes64_t frames, InsertTimeOption opt,
 
 		if (pl) {
 
+                        /* XXX STATEFUL this won't capture region motion if done as stateful diff 
+                         */
+
 			XMLNode &before = pl->get_state();
 
 			if (opt == SplitIntersected) {
diff --git a/gtk2_ardour/editor_timefx.cc b/gtk2_ardour/editor_timefx.cc
index aab6b67658..fcd7e9baf4 100644
--- a/gtk2_ardour/editor_timefx.cc
+++ b/gtk2_ardour/editor_timefx.cc
@@ -26,6 +26,7 @@
 #include "pbd/error.h"
 #include "pbd/pthread_utils.h"
 #include "pbd/memento_command.h"
+#include "pbd/stateful_diff_command.h"
 
 #include <gtkmm2ext/utils.h>
 
@@ -80,11 +81,10 @@ Editor::time_stretch (RegionSelection& regions, float fraction)
 		MidiStretch stretch(*_session, request);
 		begin_reversible_command ("midi stretch");
 		stretch.run(regions.front()->region());
-		XMLNode &before = playlist->get_state();
+                playlist->clear_history ();
 		playlist->replace_region (regions.front()->region(), stretch.results[0],
 				regions.front()->region()->position());
-		XMLNode &after = playlist->get_state();
-		_session->add_command (new MementoCommand<Playlist>(*playlist, &before, &after));
+		_session->add_command (new StatefulDiffCommand (playlist));
 		commit_reversible_command ();
 	}
 
@@ -315,10 +315,9 @@ Editor::do_timefx (TimeFXDialog& dialog)
 				in_command = true;
 			}
 
-			XMLNode &before = playlist->get_state();
+                        playlist->clear_history ();
 			playlist->replace_region (region, new_region, region->position());
-			XMLNode &after = playlist->get_state();
-			_session->add_command (new MementoCommand<Playlist>(*playlist, &before, &after));
+			_session->add_command (new StatefulDiffCommand (playlist));
 		}
 
 		i = tmp;
diff --git a/gtk2_ardour/midi_region_view.cc b/gtk2_ardour/midi_region_view.cc
index 4ea7aba4fa..aec77df8c0 100644
--- a/gtk2_ardour/midi_region_view.cc
+++ b/gtk2_ardour/midi_region_view.cc
@@ -29,6 +29,7 @@
 #include <sigc++/signal.h>
 
 #include "pbd/memento_command.h"
+#include "pbd/stateful_diff_command.h"
 
 #include "ardour/playlist.h"
 #include "ardour/tempo.h"
@@ -2530,9 +2531,9 @@ MidiRegionView::paste (nframes64_t pos, float times, const MidiCutBuffer& mcb)
 
 		trackview.session()->begin_reversible_command (_("paste"));
 
-		XMLNode& before (_region->get_state());
+                _region->clear_history ();
 		_region->set_length (end_frame, this);
-		trackview.session()->add_command (new MementoCommand<Region>(*_region, &before, &_region->get_state()));
+		trackview.session()->add_command (new StatefulDiffCommand (_region));
 	}
 
 	apply_delta ();
diff --git a/gtk2_ardour/midi_streamview.cc b/gtk2_ardour/midi_streamview.cc
index 19c1a53b39..1ca63d0f53 100644
--- a/gtk2_ardour/midi_streamview.cc
+++ b/gtk2_ardour/midi_streamview.cc
@@ -558,10 +558,10 @@ MidiStreamView::update_rec_regions (boost::shared_ptr<MidiModel> data, nframes_t
 
 					if (nlen != region->length()) {
 
-						region->freeze ();
+						region->suspend_property_changes ();
 						region->set_position (_trackview.get_diskstream()->get_capture_start_frame(n), this);
 						region->set_length (start + dur - region->position(), this);
-						region->thaw ();
+						region->resume_property_changes ();
 
 						if (origlen == 1) {
 							/* our special initial length */
@@ -622,10 +622,10 @@ MidiStreamView::update_rec_regions (boost::shared_ptr<MidiModel> data, nframes_t
 
 					if (region->source_length(0) >= region->position() + nlen) {
 
-						region->freeze ();
+						region->suspend_property_changes ();
 						region->set_position (_trackview.get_diskstream()->get_capture_start_frame(n), this);
 						region->set_length (nlen, this);
-						region->thaw ();
+						region->resume_property_changes ();
 
 						if (origlen == 1) {
 							/* our special initial length */
diff --git a/gtk2_ardour/midi_time_axis.cc b/gtk2_ardour/midi_time_axis.cc
index b1adb7c67e..5949541e56 100644
--- a/gtk2_ardour/midi_time_axis.cc
+++ b/gtk2_ardour/midi_time_axis.cc
@@ -31,6 +31,7 @@
 #include "pbd/basename.h"
 #include "pbd/enumwriter.h"
 #include "pbd/memento_command.h"
+#include "pbd/stateful_diff_command.h"
 
 #include <gtkmm2ext/gtk_ui.h>
 #include <gtkmm2ext/selector.h>
@@ -966,7 +967,7 @@ MidiTimeAxisView::add_region (nframes64_t pos)
 	Editor* real_editor = dynamic_cast<Editor*> (&_editor);
 
 	real_editor->begin_reversible_command (_("create region"));
-	XMLNode &before = playlist()->get_state();
+        playlist()->clear_history ();
 
 	framepos_t start = pos;
 	real_editor->snap_to (start, -1);
@@ -988,8 +989,7 @@ MidiTimeAxisView::add_region (nframes64_t pos)
 	boost::shared_ptr<Region> region = (RegionFactory::create (src, plist));
 
 	playlist()->add_region (region, start);
-	XMLNode &after = playlist()->get_state();
-	_session->add_command (new MementoCommand<Playlist> (*playlist().get(), &before, &after));
+	_session->add_command (new StatefulDiffCommand (playlist()));
 
 	real_editor->commit_reversible_command();
 
diff --git a/gtk2_ardour/region_gain_line.cc b/gtk2_ardour/region_gain_line.cc
index 827562524e..30e19ec24a 100644
--- a/gtk2_ardour/region_gain_line.cc
+++ b/gtk2_ardour/region_gain_line.cc
@@ -19,6 +19,7 @@
 
 #include "evoral/Curve.hpp"
 #include "pbd/memento_command.h"
+#include "pbd/stateful_diff_command.h"
 
 #include "ardour/audioregion.h"
 #include "ardour/session.h"
@@ -53,6 +54,8 @@ void
 AudioRegionGainLine::start_drag_single (ControlPoint* cp, double x, float fraction)
 {
 	AutomationLine::start_drag_single (cp, x, fraction);
+
+        // XXX Stateful need to capture automation curve data
 	
 	if (!rv.audio_region()->envelope_active()) {
 		trackview.session()->add_command(new MementoCommand<AudioRegion>(*(rv.audio_region().get()), &rv.audio_region()->get_state(), 0));
@@ -72,10 +75,9 @@ AudioRegionGainLine::remove_point (ControlPoint& cp)
 	XMLNode &before = alist->get_state();
 
 	if (!rv.audio_region()->envelope_active()) {
-		XMLNode &region_before = rv.audio_region()->get_state();
+                rv.audio_region()->clear_history ();
 		rv.audio_region()->set_envelope_active(true);
-		XMLNode &region_after = rv.audio_region()->get_state();
-		trackview.session()->add_command(new MementoCommand<AudioRegion>(*(rv.audio_region().get()), &region_before, &region_after));
+		trackview.session()->add_command(new StatefulDiffCommand (rv.audio_region()));
 	}
 
 	alist->erase (mr.start, mr.end);
diff --git a/libs/ardour/ardour/audio_track.h b/libs/ardour/ardour/audio_track.h
index fc5b4255b3..be8d988a41 100644
--- a/libs/ardour/ardour/audio_track.h
+++ b/libs/ardour/ardour/audio_track.h
@@ -49,7 +49,7 @@ class AudioTrack : public Track
 
 	int export_stuff (BufferSet& bufs, sframes_t start_frame, nframes_t nframes, bool enable_processing = true);
 
-	void freeze (InterThreadInfo&);
+	void freeze_me (InterThreadInfo&);
 	void unfreeze ();
 
 	boost::shared_ptr<Region> bounce (InterThreadInfo&);
diff --git a/libs/ardour/ardour/automation_list.h b/libs/ardour/ardour/automation_list.h
index 1778771c5f..79acedebf3 100644
--- a/libs/ardour/ardour/automation_list.h
+++ b/libs/ardour/ardour/automation_list.h
@@ -50,7 +50,6 @@ class AutomationList : public PBD::StatefulDestructible, public Evoral::ControlL
 	AutomationList& operator= (const AutomationList&);
 	bool operator== (const AutomationList&);
 
-	void freeze();
 	void thaw ();
 	void mark_dirty () const;
 
diff --git a/libs/ardour/ardour/midi_track.h b/libs/ardour/ardour/midi_track.h
index bc636eea83..6f8fda78da 100644
--- a/libs/ardour/ardour/midi_track.h
+++ b/libs/ardour/ardour/midi_track.h
@@ -53,7 +53,7 @@ public:
 
 	int export_stuff (BufferSet& bufs, nframes_t nframes, sframes_t end_frame);
 
-	void freeze (InterThreadInfo&);
+	void freeze_me (InterThreadInfo&);
 	void unfreeze ();
 
 	boost::shared_ptr<Region> bounce (InterThreadInfo&);
diff --git a/libs/ardour/ardour/region.h b/libs/ardour/ardour/region.h
index 1da185c6f2..09dd8f203c 100644
--- a/libs/ardour/ardour/region.h
+++ b/libs/ardour/ardour/region.h
@@ -93,9 +93,6 @@ class Region
 
         PBD::PropertyList* property_factory (const XMLNode&) const;
 
-	void unlock_property_changes () { _no_property_changes = false; }
-	void block_property_changes () { _no_property_changes = true; }
-	
 	virtual ~Region();
 	
 	/** Note: changing the name of a Region does not constitute an edit */
@@ -156,8 +153,7 @@ class Region
 	void set_position_lock_style (PositionLockStyle ps);
 	void recompute_position_from_lock_style ();
 
-	void freeze ();
-	void thaw ();
+	void suspend_property_changes ();
 
 	bool covers (framepos_t frame) const {
 		return first_frame() <= frame && frame <= last_frame();
@@ -288,6 +284,7 @@ class Region
 
   protected:
 	void send_change (const PBD::PropertyChange&);
+        void mid_thaw (const PBD::PropertyChange&);
 
 	void trim_to_internal (framepos_t position, framecnt_t length, void *src);
 	virtual void set_position_internal (framepos_t pos, bool allow_bbt_recompute);
@@ -304,7 +301,6 @@ class Region
 	virtual void recompute_at_end () = 0;
 	
 	DataType                _type;
-	bool                    _no_property_changes;
 
 	PBD::Property<bool>        _muted;
 	PBD::Property<bool>        _opaque;
@@ -332,14 +328,11 @@ class Region
 	framepos_t              _last_position;
 	PositionLockStyle       _positional_lock_style;
 	mutable RegionEditState _first_edit;
-	int                     _frozen;
 	BBT_Time                _bbt_time;
 	AnalysisFeatureList     _transients;
 	bool                    _valid_transients;
 	mutable uint64_t        _read_data_count;  ///< modified in read()
-	PBD::PropertyChange     _pending_changed;
 	uint64_t                _last_layer_op;  ///< timestamp
-	Glib::Mutex             _lock;
 	SourceList              _sources;
 	/** Used when timefx are applied, so we can always use the original source */
 	SourceList              _master_sources;
diff --git a/libs/ardour/ardour/session.h b/libs/ardour/ardour/session.h
index d26c84a795..cf88f2e6bd 100644
--- a/libs/ardour/ardour/session.h
+++ b/libs/ardour/ardour/session.h
@@ -603,7 +603,7 @@ class Session : public PBD::StatefulDestructible, public PBD::ScopedConnectionLi
 	boost::shared_ptr<Region> write_one_track (AudioTrack&, nframes_t start, nframes_t end,
 			bool overwrite, std::vector<boost::shared_ptr<Source> >&, InterThreadInfo& wot,
 			bool enable_processing = true);
-	int freeze (InterThreadInfo&);
+	int freeze_all (InterThreadInfo&);
 
 	/* session-wide solo/mute/rec-enable */
 
diff --git a/libs/ardour/ardour/track.h b/libs/ardour/ardour/track.h
index 0ed4b8c70b..eee9f03fe5 100644
--- a/libs/ardour/ardour/track.h
+++ b/libs/ardour/ardour/track.h
@@ -74,7 +74,7 @@ class Track : public Route
 
 	FreezeState freeze_state() const;
 
-	virtual void freeze (InterThreadInfo&) = 0;
+	virtual void freeze_me (InterThreadInfo&) = 0;
 	virtual void unfreeze () = 0;
 
 	virtual boost::shared_ptr<Region> bounce (InterThreadInfo&) = 0;
diff --git a/libs/ardour/audio_diskstream.cc b/libs/ardour/audio_diskstream.cc
index f7a1240bdd..1f77964d0d 100644
--- a/libs/ardour/audio_diskstream.cc
+++ b/libs/ardour/audio_diskstream.cc
@@ -35,7 +35,7 @@
 #include "pbd/xml++.h"
 #include "pbd/memento_command.h"
 #include "pbd/enumwriter.h"
-#include "pbd/stacktrace.h"
+#include "pbd/stateful_diff_command.h"
 
 #include "ardour/analyser.h"
 #include "ardour/ardour.h"
@@ -1497,7 +1497,7 @@ AudioDiskstream::transport_stopped (struct tm& when, time_t twhen, bool abort_ca
 
 		// cerr << _name << ": there are " << capture_info.size() << " capture_info records\n";
 
-		XMLNode &before = _playlist->get_state();
+                _playlist->clear_history ();
 		_playlist->freeze ();
 
 		for (buffer_position = c->front()->write_source->last_capture_start_frame(), ci = capture_info.begin(); ci != capture_info.end(); ++ci) {
@@ -1537,8 +1537,7 @@ AudioDiskstream::transport_stopped (struct tm& when, time_t twhen, bool abort_ca
 		}
 
 		_playlist->thaw ();
-		XMLNode &after = _playlist->get_state();
-		_session.add_command (new MementoCommand<Playlist>(*_playlist, &before, &after));
+		_session.add_command (new StatefulDiffCommand (_playlist));
 	}
 
 	mark_write_completed = true;
diff --git a/libs/ardour/audio_track.cc b/libs/ardour/audio_track.cc
index ebc7a9be66..245b122c18 100644
--- a/libs/ardour/audio_track.cc
+++ b/libs/ardour/audio_track.cc
@@ -692,7 +692,7 @@ AudioTrack::bounce_range (nframes_t start, nframes_t end, InterThreadInfo& itt,
 }
 
 void
-AudioTrack::freeze (InterThreadInfo& itt)
+AudioTrack::freeze_me (InterThreadInfo& itt)
 {
 	vector<boost::shared_ptr<Source> > srcs;
 	string new_playlist_name;
diff --git a/libs/ardour/audioregion.cc b/libs/ardour/audioregion.cc
index e30a3a5994..abddffc12e 100644
--- a/libs/ardour/audioregion.cc
+++ b/libs/ardour/audioregion.cc
@@ -589,7 +589,7 @@ AudioRegion::_set_state (const XMLNode& node, int version, PropertyChange& what_
 	LocaleGuard lg (X_("POSIX"));
 	boost::shared_ptr<Playlist> the_playlist (_playlist.lock());	
 
-	freeze ();
+	suspend_property_changes ();
 
 	if (the_playlist) {
 		the_playlist->freeze ();
@@ -612,7 +612,7 @@ AudioRegion::_set_state (const XMLNode& node, int version, PropertyChange& what_
 
 	/* Now find envelope description and other related child items */
 
-	_envelope->freeze ();
+        _envelope->freeze ();
 
 	for (XMLNodeConstIterator niter = nlist.begin(); niter != nlist.end(); ++niter) {
 		XMLNode *child;
@@ -677,9 +677,9 @@ AudioRegion::_set_state (const XMLNode& node, int version, PropertyChange& what_
 		}
 	}
 
-	_envelope->thaw ();
-	thaw ();
-
+        _envelope->thaw ();
+	resume_property_changes ();
+        
 	if (send) {
 		send_change (what_changed);
 	}
@@ -761,9 +761,9 @@ AudioRegion::set_fade_out_shape (FadeShape shape)
 void
 AudioRegion::set_fade_in (boost::shared_ptr<AutomationList> f)
 {
-	_fade_in->freeze ();
+        _fade_in->freeze ();
 	*_fade_in = *f;
-	_fade_in->thaw ();
+        _fade_in->thaw ();
 	
 	send_change (PropertyChange (Properties::fade_in));
 }
@@ -771,7 +771,7 @@ AudioRegion::set_fade_in (boost::shared_ptr<AutomationList> f)
 void
 AudioRegion::set_fade_in (FadeShape shape, framecnt_t len)
 {
-	_fade_in->freeze ();
+        _fade_in->freeze ();
 	_fade_in->clear ();
 
 	switch (shape) {
@@ -822,15 +822,15 @@ AudioRegion::set_fade_in (FadeShape shape, framecnt_t len)
 		break;
 	}
 
-	_fade_in->thaw ();
+        _fade_in->thaw ();
 }
 
 void
 AudioRegion::set_fade_out (boost::shared_ptr<AutomationList> f)
 {
-	_fade_out->freeze ();
+        _fade_out->freeze ();
 	*_fade_out = *f;
-	_fade_out->thaw ();
+        _fade_out->thaw ();
 
 	send_change (PropertyChange (Properties::fade_in));
 }
@@ -838,7 +838,7 @@ AudioRegion::set_fade_out (boost::shared_ptr<AutomationList> f)
 void
 AudioRegion::set_fade_out (FadeShape shape, framecnt_t len)
 {
-	_fade_out->freeze ();
+        _fade_out->freeze ();
 	_fade_out->clear ();
 
 	switch (shape) {
@@ -887,7 +887,7 @@ AudioRegion::set_fade_out (FadeShape shape, framecnt_t len)
 		break;
 	}
 
-	_fade_out->thaw ();
+        _fade_out->thaw ();
 }
 
 void
@@ -977,11 +977,11 @@ AudioRegion::set_default_fades ()
 void
 AudioRegion::set_default_envelope ()
 {
-	_envelope->freeze ();
+        _envelope->freeze ();
 	_envelope->clear ();
 	_envelope->fast_simple_add (0, 1.0f);
 	_envelope->fast_simple_add (_length, 1.0f);
-	_envelope->thaw ();
+        _envelope->thaw ();
 }
 
 void
@@ -991,10 +991,10 @@ AudioRegion::recompute_at_end ()
 	   based on the the existing curve.
 	*/
 
-	_envelope->freeze ();
+        _envelope->freeze ();
 	_envelope->truncate_end (_length);
 	_envelope->set_max_xval (_length);
-	_envelope->thaw ();
+        _envelope->thaw ();
 
 	if (_fade_in->back()->when > _length) {
 		_fade_in->extend_to (_length);
diff --git a/libs/ardour/automation_list.cc b/libs/ardour/automation_list.cc
index 479674aee6..92a3d167da 100644
--- a/libs/ardour/automation_list.cc
+++ b/libs/ardour/automation_list.cc
@@ -170,7 +170,7 @@ AutomationList::maybe_signal_changed ()
 {
 	ControlList::maybe_signal_changed ();
 
-	if (!_frozen) {
+	if (!ControlList::frozen()) {
 		StateChanged (); /* EMIT SIGNAL */
 	}
 }
@@ -208,12 +208,6 @@ AutomationList::stop_touch ()
 }
 
 void
-AutomationList::freeze ()
-{
-	_frozen++;
-}
-
-void
 AutomationList::thaw ()
 {
 	ControlList::thaw();
@@ -313,7 +307,7 @@ AutomationList::deserialize_events (const XMLNode& node)
 		return -1;
 	}
 
-	freeze ();
+        ControlList::freeze ();
 	clear ();
 
 	stringstream str (content_node->content());
@@ -344,8 +338,8 @@ AutomationList::deserialize_events (const XMLNode& node)
 		maybe_signal_changed ();
 	}
 
-	thaw ();
-
+        ControlList::thaw ();
+        
 	return 0;
 }
 
@@ -377,7 +371,7 @@ AutomationList::set_state (const XMLNode& node, int version)
 		nframes_t x;
 		double y;
 
-		freeze ();
+                ControlList::freeze ();
 		clear ();
 
 		for (i = elist.begin(); i != elist.end(); ++i) {
@@ -397,7 +391,7 @@ AutomationList::set_state (const XMLNode& node, int version)
 			fast_simple_add (x, y);
 		}
 
-		thaw ();
+                ControlList::thaw ();
 
 		return 0;
 	}
diff --git a/libs/ardour/midi_diskstream.cc b/libs/ardour/midi_diskstream.cc
index ccfaeaa5cd..836fb05c8b 100644
--- a/libs/ardour/midi_diskstream.cc
+++ b/libs/ardour/midi_diskstream.cc
@@ -35,6 +35,7 @@
 #include "pbd/xml++.h"
 #include "pbd/memento_command.h"
 #include "pbd/enumwriter.h"
+#include "pbd/stateful_diff_command.h"
 
 #include "ardour/ardour.h"
 #include "ardour/audioengine.h"
@@ -1011,7 +1012,7 @@ MidiDiskstream::transport_stopped (struct tm& /*when*/, time_t /*twhen*/, bool a
 
 		// cerr << _name << ": there are " << capture_info.size() << " capture_info records\n";
 
-		XMLNode &before = _playlist->get_state();
+		_playlist->clear_history ();
 		_playlist->freeze ();
 
 		uint32_t buffer_position = 0;
@@ -1053,8 +1054,7 @@ MidiDiskstream::transport_stopped (struct tm& /*when*/, time_t /*twhen*/, bool a
 		}
 
 		_playlist->thaw ();
-		XMLNode &after = _playlist->get_state();
-		_session.add_command (new MementoCommand<Playlist>(*_playlist, &before, &after));
+		_session.add_command (new StatefulDiffCommand(_playlist));
 
 	}
 
diff --git a/libs/ardour/midi_track.cc b/libs/ardour/midi_track.cc
index af66f2f40c..9409e9f143 100644
--- a/libs/ardour/midi_track.cc
+++ b/libs/ardour/midi_track.cc
@@ -556,7 +556,7 @@ MidiTrack::bounce_range (nframes_t /*start*/, nframes_t /*end*/, InterThreadInfo
 }
 
 void
-MidiTrack::freeze (InterThreadInfo& /*itt*/)
+MidiTrack::freeze_me (InterThreadInfo& /*itt*/)
 {
 }
 
diff --git a/libs/ardour/playlist.cc b/libs/ardour/playlist.cc
index 6169df8f03..eb21cdcde6 100644
--- a/libs/ardour/playlist.cc
+++ b/libs/ardour/playlist.cc
@@ -855,7 +855,7 @@ Playlist::partition (framepos_t start, framepos_t end, bool cut)
 	partition_internal (start, end, cut, thawlist);
 
 	for (RegionList::iterator i = thawlist.begin(); i != thawlist.end(); ++i) {
-		(*i)->thaw ();
+		(*i)->resume_property_changes ();
 	}
 }
 
@@ -972,7 +972,7 @@ Playlist::partition_internal (framepos_t start, framepos_t end, bool cutting, Re
 
 				/* "front" ***** */
 
-				current->freeze ();
+				current->suspend_property_changes ();
 				thawlist.push_back (current);
 				current->trim_end (pos2, this);
 
@@ -1011,7 +1011,7 @@ Playlist::partition_internal (framepos_t start, framepos_t end, bool cutting, Re
 
 				/* front ****** */
 
-				current->freeze ();
+				current->suspend_property_changes ();
 				thawlist.push_back (current);
 				current->trim_end (pos2, this);
 
@@ -1054,7 +1054,7 @@ Playlist::partition_internal (framepos_t start, framepos_t end, bool cutting, Re
 
 				/* end */
 
-				current->freeze ();
+				current->suspend_property_changes ();
 				thawlist.push_back (current);
 				current->trim_front (pos3, this);
 			} else if (overlap == OverlapExternal) {
@@ -1157,7 +1157,7 @@ Playlist::cut (framepos_t start, framecnt_t cnt, bool result_is_hidden)
 	partition_internal (start, start+cnt-1, true, thawlist);
 
 	for (RegionList::iterator i = thawlist.begin(); i != thawlist.end(); ++i) {
-		(*i)->thaw ();
+		(*i)->resume_property_changes();
 	}
 
 	return the_copy;
@@ -2123,15 +2123,15 @@ Playlist::set_state (const XMLNode& node, int version)
 
 			if ((region = region_by_id (id))) {
 
-				region->freeze ();
+				region->suspend_property_changes ();
 
 				if (region->set_state (*child, version)) {
-					region->thaw ();
+					region->resume_property_changes ();
 					continue;
 				}
 				
 			} else if ((region = RegionFactory::create (_session, *child, true)) != 0) {
-				region->freeze ();
+				region->suspend_property_changes ();
 			} else {
 				error << _("Playlist: cannot create region from XML") << endmsg;
 				continue;
@@ -2141,7 +2141,7 @@ Playlist::set_state (const XMLNode& node, int version)
 
 			// So that layer_op ordering doesn't get screwed up
 			region->set_last_layer_op( region->layer());
-			region->thaw ();
+			region->resume_property_changes ();
 		}
 	}
 
diff --git a/libs/ardour/region.cc b/libs/ardour/region.cc
index f59d076c59..b89ad2854b 100644
--- a/libs/ardour/region.cc
+++ b/libs/ardour/region.cc
@@ -199,13 +199,11 @@ Region::register_properties ()
 Region::Region (Session& s, framepos_t start, framecnt_t length, const string& name, DataType type)
 	: SessionObject(s, name)
 	, _type(type)
-	, _no_property_changes (true)
 	, REGION_DEFAULT_STATE(start,length)
 	, _last_length (length)
 	, _last_position (0)
 	, _positional_lock_style(AudioTime)
 	, _first_edit (EditChangesNothing)
-	, _frozen(0)
 	, _read_data_count(0)
 	, _last_layer_op(0)
 	, _pending_explicit_relayer (false)
@@ -219,13 +217,11 @@ Region::Region (Session& s, framepos_t start, framecnt_t length, const string& n
 Region::Region (const SourceList& srcs)
 	: SessionObject(srcs.front()->session(), "toBeRenamed")
 	, _type (srcs.front()->type())
-	, _no_property_changes (true)
 	, REGION_DEFAULT_STATE(0,0)
 	, _last_length (0)
 	, _last_position (0)
         , _positional_lock_style (_type == DataType::AUDIO ? AudioTime : MusicTime)
 	, _first_edit (EditChangesNothing)
-	, _frozen (0)
 	, _valid_transients(false)
 	, _read_data_count(0)
 	, _last_layer_op (0)
@@ -251,13 +247,11 @@ Region::Region (const SourceList& srcs)
 Region::Region (boost::shared_ptr<const Region> other, frameoffset_t offset, bool offset_relative)
 	: SessionObject(other->session(), other->name())
 	, _type (other->data_type())
-	, _no_property_changes (true)
 	, REGION_COPY_STATE (other)
 	, _last_length (other->_last_length)
 	, _last_position(other->_last_position) \
 	, _positional_lock_style(other->_positional_lock_style) \
 	, _first_edit (EditChangesNothing)
-	, _frozen (0)
 	, _valid_transients(false)
 	, _read_data_count(0)
 	, _last_layer_op (0)
@@ -360,13 +354,11 @@ Region::Region (boost::shared_ptr<const Region> other, frameoffset_t offset, boo
 Region::Region (boost::shared_ptr<const Region> other, const SourceList& srcs)
 	: SessionObject (other->session(), other->name())
 	, _type (srcs.front()->type())
-	, _no_property_changes (true)
 	, REGION_COPY_STATE (other)
 	, _last_length (other->_last_length)
 	, _last_position (other->_last_position)
         , _positional_lock_style (other->_positional_lock_style)
 	, _first_edit (EditChangesID)
-	, _frozen (0)
 	, _valid_transients (false)
 	, _read_data_count (0)
 	, _last_layer_op (other->_last_layer_op)
@@ -393,13 +385,11 @@ Region::Region (boost::shared_ptr<const Region> other, const SourceList& srcs)
 Region::Region (boost::shared_ptr<const Region> other)
 	: SessionObject(other->session(), other->name())
 	, _type(other->data_type())
-	, _no_property_changes (true)
 	, REGION_COPY_STATE (other)
 	, _last_length (other->_last_length)
 	, _last_position (other->_last_position)
         , _positional_lock_style (other->_positional_lock_style)
 	, _first_edit (EditChangesID)
-	, _frozen(0)
 	, _valid_transients(false)
 	, _read_data_count(0)
 	, _last_layer_op(other->_last_layer_op)
@@ -475,7 +465,7 @@ Region::set_length (framecnt_t len, void */*src*/)
 		maybe_uncopy ();
 		invalidate_transients ();
 
-		if (!_frozen) {
+		if (!property_changes_suspended()) {
 			recompute_at_end ();
 		}
 
@@ -803,7 +793,7 @@ Region::trim_front (framepos_t new_position, void *src)
 		}
 
 		trim_to_internal (new_position, newlen, src);
-		if (!_frozen) {
+		if (!property_changes_suspended()) {
 			recompute_at_start ();
 		}
 	}
@@ -822,7 +812,7 @@ Region::trim_end (framepos_t new_endpoint, void */*src*/)
 
 	if (new_endpoint > _position) {
 		trim_to_internal (_position, new_endpoint - _position + 1, this);
-		if (!_frozen) {
+		if (!property_changes_suspended()) {
 			recompute_at_end ();
 		}
 	}
@@ -837,7 +827,7 @@ Region::trim_to (framepos_t position, framecnt_t length, void *src)
 
 	trim_to_internal (position, length, src);
 
-	if (!_frozen) {
+	if (!property_changes_suspended()) {
 		recompute_at_start ();
 		recompute_at_end ();
 	}
@@ -890,14 +880,14 @@ Region::trim_to_internal (framepos_t position, framecnt_t length, void */*src*/)
 		what_changed.add (Properties::start);
 	}
 	if (_length != length) {
-		if (!_frozen) {
+		if (!property_changes_suspended()) {
 			_last_length = _length;
 		}
 		_length = length;
 		what_changed.add (Properties::length);
 	}
 	if (_position != position) {
-		if (!_frozen) {
+		if (!property_changes_suspended()) {
 			_last_position = _position;
 		}
 		_position = position;
@@ -987,7 +977,7 @@ Region::set_sync_position (framepos_t absolute_pos)
 	if (file_pos != _sync_position) {
 		_sync_marked = true;
 		_sync_position = file_pos;
-		if (!_frozen) {
+		if (!property_changes_suspended()) {
 			maybe_uncopy ();
 		}
 		send_change (Properties::sync_position);
@@ -999,7 +989,7 @@ Region::clear_sync_position ()
 {
 	if (sync_marked()) {
 		_sync_marked = false;
-		if (!_frozen) {
+		if (!property_changes_suspended()) {
 			maybe_uncopy ();
 		}
 		send_change (Properties::sync_position);
@@ -1229,43 +1219,22 @@ Region::_set_state (const XMLNode& node, int version, PropertyChange& what_chang
 }
 
 void
-Region::freeze ()
+Region::suspend_property_changes ()
 {
-	_frozen++;
+        Stateful::suspend_property_changes ();
 	_last_length = _length;
 	_last_position = _position;
 }
 
 void
-Region::thaw ()
+Region::mid_thaw (const PropertyChange& what_changed)
 {
-	PropertyChange what_changed;
-
-	{
-		Glib::Mutex::Lock lm (_lock);
-
-		if (_frozen && --_frozen > 0) {
-			return;
-		}
-
-		if (!_pending_changed.empty()) {
-			what_changed = _pending_changed;
-			_pending_changed.clear ();
-		}
-	}
-
-	if (what_changed.empty()) {
-		return;
-	}
-
 	if (what_changed.contains (Properties::length)) {
 		if (what_changed.contains (Properties::position)) {
 			recompute_at_start ();
 		}
 		recompute_at_end ();
 	}
-
-	send_change (what_changed);
 }
 
 void
@@ -1275,15 +1244,7 @@ Region::send_change (const PropertyChange& what_changed)
 		return;
 	}
 
-	{
-		Glib::Mutex::Lock lm (_lock);
-		if (_frozen) {
-			_pending_changed.add (what_changed);
-			return;
-		}
-	}
-
-	PropertyChanged (what_changed);
+        Stateful::send_change (what_changed);
 
 	if (!_no_property_changes) {
 		
@@ -1294,12 +1255,10 @@ Region::send_change (const PropertyChange& what_changed)
 		try {
 			boost::shared_ptr<Region> rptr = shared_from_this();
 			RegionPropertyChanged (rptr, what_changed);
-
 		} catch (...) {
 			/* no shared_ptr available, relax; */
 		}
 	}
-
 }
 
 void
@@ -1584,16 +1543,26 @@ Region::set_property (const PropertyBase& prop)
 	} else if (prop == Properties::position_locked.property_id) {
 		_position_locked = dynamic_cast<const PropertyTemplate<bool>*>(&prop)->val();
 	} else if (prop == Properties::start.property_id) {
-		_start = dynamic_cast<const PropertyTemplate<framepos_t>*>(&prop)->val();
+		framepos_t val = dynamic_cast<const PropertyTemplate<framepos_t>*>(&prop)->val();
+                if (val != _start) {
+                        DEBUG_TRACE (DEBUG::Properties, string_compose ("region %1 start changed from %2 to %3",
+									_name.val(), _start, val));
+                        _start = val;
+                        return true;
+                }
 	} else if (prop == Properties::length.property_id) {
 		framecnt_t val = dynamic_cast<const PropertyTemplate<framecnt_t>* > (&prop)->val();
 		if (val != _length) {
+			DEBUG_TRACE (DEBUG::Properties, string_compose ("region %1 length changed from %2 to %3",
+									_name.val(), _length, val));
 			_length = val;
 			return true;
 		}
 	} else if (prop == Properties::position.property_id) {
 		framepos_t val = dynamic_cast<const PropertyTemplate<framepos_t>*>(&prop)->val();
 		if (val != _position) {
+			DEBUG_TRACE (DEBUG::Properties, string_compose ("region %1 position changed from %2 to %3",
+									_name.val(), _position, val));
 			_position = val;
 			return true;
 		}
diff --git a/libs/ardour/region_factory.cc b/libs/ardour/region_factory.cc
index d2c5fa1b22..3f4af2462c 100644
--- a/libs/ardour/region_factory.cc
+++ b/libs/ardour/region_factory.cc
@@ -67,7 +67,6 @@ RegionFactory::create (boost::shared_ptr<const Region> region)
 	}
 
 	if (ret) {
-		ret->unlock_property_changes ();
 		map_add (ret);
 
 		/* pure copy constructor - no property list */
@@ -106,10 +105,7 @@ RegionFactory::create (boost::shared_ptr<Region> region, frameoffset_t offset, c
 	}
 
 	if (ret) {
-
 		ret->set_properties (plist);
-		ret->unlock_property_changes ();
-
 		map_add (ret);
 
 		if (announce) {
@@ -149,10 +145,7 @@ RegionFactory::create (boost::shared_ptr<Region> region, const PropertyList& pli
 	}
 
 	if (ret) {
-
 		ret->set_properties (plist);
-		ret->unlock_property_changes ();
-
 		map_add (ret);
 
 		if (announce) {
@@ -195,8 +188,6 @@ RegionFactory::create (boost::shared_ptr<Region> region, const SourceList& srcs,
 	if (ret) {
 
 		ret->set_properties (plist);
-		ret->unlock_property_changes ();
-
 		map_add (ret);
 
 		if (announce) {
@@ -242,8 +233,6 @@ RegionFactory::create (const SourceList& srcs, const PropertyList& plist, bool a
 	if (ret) {
 
 		ret->set_properties (plist);
-		ret->unlock_property_changes ();
-
 		map_add (ret);
 
 		if (announce) {
@@ -290,7 +279,6 @@ RegionFactory::create (SourceList& srcs, const XMLNode& node)
 		if (ret->set_state (node, Stateful::loading_state_version)) {
 			ret.reset ();
 		} else {
-			ret->unlock_property_changes ();
 			map_add (ret);
 			CheckNewRegion (ret);
 		}
diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index 0c2f12d91d..53c8ea2350 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -3847,7 +3847,7 @@ Session::allocate_pan_automation_buffers (nframes_t nframes, uint32_t howmany, b
 }
 
 int
-Session::freeze (InterThreadInfo& itt)
+Session::freeze_all (InterThreadInfo& itt)
 {
 	shared_ptr<RouteList> r = routes.reader ();
 
@@ -3859,7 +3859,7 @@ Session::freeze (InterThreadInfo& itt)
 			/* XXX this is wrong because itt.progress will keep returning to zero at the start
 			   of every track.
 			*/
-			t->freeze (itt);
+			t->freeze_me (itt);
 		}
 	}
 
diff --git a/libs/evoral/evoral/ControlList.hpp b/libs/evoral/evoral/ControlList.hpp
index b4c8590cb6..d68b6a3e5f 100644
--- a/libs/evoral/evoral/ControlList.hpp
+++ b/libs/evoral/evoral/ControlList.hpp
@@ -94,8 +94,9 @@ public:
 	ControlList& operator= (const ControlList&);
 	bool operator== (const ControlList&);
 
-	void freeze();
-	void thaw ();
+	virtual void freeze();
+        virtual void thaw ();
+        bool frozen() const { return _frozen; }
 
 	const Parameter& parameter() const                 { return _parameter; }
 	void             set_parameter(const Parameter& p) { _parameter = p; }
diff --git a/libs/pbd/pbd/properties.h b/libs/pbd/pbd/properties.h
index 274dfffd9c..8d2f465ebf 100644
--- a/libs/pbd/pbd/properties.h
+++ b/libs/pbd/pbd/properties.h
@@ -122,8 +122,10 @@ protected:
 	{}
 
 	void set (T const& v) {
-		_old      = _current;
-		_have_old = true;
+                if (!_have_old) {
+                        _old      = _current;
+                        _have_old = true;
+                }
 		_current  = v;
 	}
 
diff --git a/libs/pbd/pbd/stateful.h b/libs/pbd/pbd/stateful.h
index 78b9eb7b3b..93f353a095 100644
--- a/libs/pbd/pbd/stateful.h
+++ b/libs/pbd/pbd/stateful.h
@@ -82,6 +82,12 @@ class Stateful {
 	static int current_state_version;
 	static int loading_state_version;
 
+	virtual void suspend_property_changes ();
+	virtual void resume_property_changes ();
+
+	void unlock_property_changes () { _no_property_changes = false; }
+	void block_property_changes () { _no_property_changes = true; }
+	
   protected:
 
 	void add_instant_xml (XMLNode&, const sys::path& directory_path);
@@ -100,10 +106,21 @@ class Stateful {
 
 	XMLNode *_extra_xml;
 	XMLNode *_instant_xml;
-	PBD::ID _id;
+	PBD::ID  _id;
+        int32_t  _frozen;
+        bool     _no_property_changes;
+	PBD::PropertyChange     _pending_changed;
+        Glib::Mutex _lock;
 
 	std::string _xml_node_name; ///< name of node to use for this object in XML
 	OwnedPropertyList* _properties;
+
+        virtual void send_change (const PropertyChange&);
+        /** derived classes can implement this in order to process a property change
+            within thaw() just before send_change() is called.
+        */
+        virtual void mid_thaw (const PropertyChange&) { }
+        bool property_changes_suspended() const { return g_atomic_int_get (&_frozen) > 0; }
 };
 
 } // namespace PBD
diff --git a/libs/pbd/stateful.cc b/libs/pbd/stateful.cc
index f2d9f9ee12..1bf8c17d83 100644
--- a/libs/pbd/stateful.cc
+++ b/libs/pbd/stateful.cc
@@ -39,7 +39,9 @@ int Stateful::current_state_version = 0;
 int Stateful::loading_state_version = 0;
 
 Stateful::Stateful ()
-        : _properties (new OwnedPropertyList)
+        : _frozen (0)
+        , _no_property_changes (false)
+        , _properties (new OwnedPropertyList)
 {
 	_extra_xml = 0;
 	_instant_xml = 0;
@@ -238,4 +240,52 @@ Stateful::add_property (PropertyBase& s)
         _properties->add (s);
 }
 
+void
+Stateful::send_change (const PropertyChange& what_changed)
+{
+	if (what_changed.empty()) {
+		return;
+	}
+
+	{
+		Glib::Mutex::Lock lm (_lock);
+		if (_frozen) {
+			_pending_changed.add (what_changed);
+			return;
+		}
+	}
+
+	PropertyChanged (what_changed);
+}
+
+void
+Stateful::suspend_property_changes ()
+{
+        _frozen++;
+}
+
+void
+Stateful::resume_property_changes ()
+{
+	PropertyChange what_changed;
+
+	{
+		Glib::Mutex::Lock lm (_lock);
+
+		if (_frozen && --_frozen > 0) {
+			return;
+		}
+
+		if (!_pending_changed.empty()) {
+			what_changed = _pending_changed;
+			_pending_changed.clear ();
+		}
+	}
+
+        mid_thaw (what_changed);
+
+        send_change (what_changed);
+}
+
+
 } // namespace PBD
diff --git a/libs/surfaces/osc/osc_controllable.cc b/libs/surfaces/osc/osc_controllable.cc
index baf888667e..001eca6f3e 100644
--- a/libs/surfaces/osc/osc_controllable.cc
+++ b/libs/surfaces/osc/osc_controllable.cc
@@ -36,7 +36,7 @@ OSCControllable::OSCControllable (lo_address a, const std::string& p, boost::sha
 	, addr (a)
 	, path (p)
 {
-	c->Changed.connect (changed_connection, boost::bind (&OSCControllable::send_change, this), OSC::instance());
+	c->Changed.connect (changed_connection, boost::bind (&OSCControllable::send_change_message, this), OSC::instance());
 }
 
 OSCControllable::~OSCControllable ()
@@ -58,7 +58,7 @@ OSCControllable::set_state (const XMLNode& /*node*/, int /*version*/)
 }
 
 void
-OSCControllable::send_change ()
+OSCControllable::send_change_message ()
 {
 	lo_message msg = lo_message_new ();
 	
@@ -84,7 +84,7 @@ OSCRouteControllable::~OSCRouteControllable ()
 }
 
 void
-OSCRouteControllable::send_change ()
+OSCRouteControllable::send_change_message ()
 {
 	lo_message msg = lo_message_new ();
 
diff --git a/libs/surfaces/osc/osc_controllable.h b/libs/surfaces/osc/osc_controllable.h
index 55e2815d35..828c3769f5 100644
--- a/libs/surfaces/osc/osc_controllable.h
+++ b/libs/surfaces/osc/osc_controllable.h
@@ -50,7 +50,7 @@ class OSCControllable : public PBD::Stateful
 	lo_address addr;
 	std::string path;
 
-	virtual void send_change ();
+	virtual void send_change_message ();
 };
 
 class OSCRouteControllable : public OSCControllable
@@ -67,7 +67,7 @@ class OSCRouteControllable : public OSCControllable
   private:
 	boost::shared_ptr<ARDOUR::Route> _route;
 
-	void send_change ();
+	void send_change_message ();
 };
 
 #endif /* __osc_osccontrollable_h__ */