diff --git a/src/ActionManager.cpp b/src/ActionManager.cpp
index 23f5f8d..84c7a3e 100644
--- a/src/ActionManager.cpp
+++ b/src/ActionManager.cpp
@@ -65,6 +65,8 @@ void Action::init()
     store("Session start");
 }
 
+// must be called in a thread running in parrallel of the rendering
+// (needs opengl update to get thumbnail)
 void captureMixerSession(Session *se, tinyxml2::XMLDocument *doc, std::string node, std::string label)
 {
     if (se != nullptr) {
@@ -101,6 +103,8 @@ void captureMixerSession(Session *se, tinyxml2::XMLDocument *doc, std::string no
 
 void Action::store(const std::string &label)
 {
+    // TODO: set a maximum amount of stored steps? (even very big, just to ensure memory limit)
+
     // ignore if locked or if no label is given
     if (locked_ || label.empty())
         return;
diff --git a/src/CloneSource.cpp b/src/CloneSource.cpp
index 0f33854..5e46416 100644
--- a/src/CloneSource.cpp
+++ b/src/CloneSource.cpp
@@ -228,8 +228,7 @@ uint CloneSource::texture() const
 void CloneSource::accept(Visitor& v)
 {
     Source::accept(v);
-    if (!failed())
-        v.visit(*this);
+    v.visit(*this);
 }
 
 glm::ivec2 CloneSource::icon() const
diff --git a/src/DeviceSource.cpp b/src/DeviceSource.cpp
index 0497687..f460b56 100644
--- a/src/DeviceSource.cpp
+++ b/src/DeviceSource.cpp
@@ -522,8 +522,7 @@ void DeviceSource::setActive (bool on)
 void DeviceSource::accept(Visitor& v)
 {
     Source::accept(v);
-    if (!failed())
-        v.visit(*this);
+    v.visit(*this);
 }
 
 bool DeviceSource::failed() const
diff --git a/src/ImGuiVisitor.cpp b/src/ImGuiVisitor.cpp
index ec024a8..e1af4b9 100644
--- a/src/ImGuiVisitor.cpp
+++ b/src/ImGuiVisitor.cpp
@@ -376,166 +376,200 @@ void ImGuiVisitor::visit(ImageProcessingShader &n)
 
 void ImGuiVisitor::visit (Source& s)
 {
-    ImGui::PushID(std::to_string(s.id()).c_str());
-    // blending
-    s.blendingShader()->accept(*this);
+    const float preview_width = ImGui::GetContentRegionAvail().x IMGUI_RIGHT_ALIGN;
+    const float preview_height = 4.5f * ImGui::GetFrameHeightWithSpacing();
+    const float space = ImGui::GetStyle().ItemSpacing.y;
 
-    // preview
-    float preview_width = ImGui::GetContentRegionAvail().x IMGUI_RIGHT_ALIGN;
-    float preview_height = 4.5f * ImGui::GetFrameHeightWithSpacing();
-    ImVec2 pos = ImGui::GetCursorPos(); // remember where we were...
+    if ( !s.failed() ) {
 
-    float space = ImGui::GetStyle().ItemSpacing.y;
-    float width = preview_width;
-    float height = s.frame()->projectionArea().y * width / ( s.frame()->projectionArea().x * s.frame()->aspectRatio());
-    if (height > preview_height - space) {
-        height = preview_height - space;
-        width = height * s.frame()->aspectRatio() * ( s.frame()->projectionArea().x / s.frame()->projectionArea().y);
-    }
-    // centered image
-    ImGui::SetCursorPos( ImVec2(pos.x + 0.5f * (preview_width-width), pos.y + 0.5f * (preview_height-height-space)) );
-    ImGui::Image((void*)(uintptr_t) s.frame()->texture(), ImVec2(width, height));
+        ImGui::PushID(std::to_string(s.id()).c_str());
 
-    // inform on visibility status
-    ImGui::SetCursorPos( ImVec2(preview_width + 20, pos.y ) );
-    if (s.active()) {
-        if (s.blendingShader()->color.a > 0.f)
-            ImGuiToolkit::Indication("Visible", ICON_FA_EYE);
+        // blending selection
+        s.blendingShader()->accept(*this);
+
+        // remember where we were...
+        ImVec2 pos = ImGui::GetCursorPos();
+
+        // preview
+        float width = preview_width;
+        float height = s.frame()->projectionArea().y * width / ( s.frame()->projectionArea().x * s.frame()->aspectRatio());
+        if (height > preview_height - space) {
+            height = preview_height - space;
+            width = height * s.frame()->aspectRatio() * ( s.frame()->projectionArea().x / s.frame()->projectionArea().y);
+        }
+        // centered image
+        ImGui::SetCursorPos( ImVec2(pos.x + 0.5f * (preview_width-width), pos.y + 0.5f * (preview_height-height-space)) );
+        ImGui::Image((void*)(uintptr_t) s.frame()->texture(), ImVec2(width, height));
+
+        // inform on visibility status
+        ImGui::SetCursorPos( ImVec2(preview_width + 20, pos.y ) );
+        if (s.active()) {
+            if (s.blendingShader()->color.a > 0.f)
+                ImGuiToolkit::Indication("Visible", ICON_FA_EYE);
+            else
+                ImGuiToolkit::Indication("Not visible", ICON_FA_EYE_SLASH);
+        }
         else
-            ImGuiToolkit::Indication("Not visible", ICON_FA_EYE_SLASH);
-    }
-    else
-        ImGuiToolkit::Indication("Inactive", ICON_FA_SNOWFLAKE);
+            ImGuiToolkit::Indication("Inactive", ICON_FA_SNOWFLAKE);
 
-    // Inform on workspace
-    ImGui::SetCursorPos( ImVec2(preview_width + 20, pos.y + ImGui::GetFrameHeightWithSpacing()) );
-    if (s.workspace() == Source::BACKGROUND)
-        ImGuiToolkit::Indication("in Background",10, 16);
-    else if (s.workspace() == Source::FOREGROUND)
-        ImGuiToolkit::Indication("in Foreground",12, 16);
-    else
-        ImGuiToolkit::Indication("in Workspace",11, 16);
+        // Inform on workspace
+        ImGui::SetCursorPos( ImVec2(preview_width + 20, pos.y + ImGui::GetFrameHeightWithSpacing()) );
+        if (s.workspace() == Source::BACKGROUND)
+            ImGuiToolkit::Indication("in Background",10, 16);
+        else if (s.workspace() == Source::FOREGROUND)
+            ImGuiToolkit::Indication("in Foreground",12, 16);
+        else
+            ImGuiToolkit::Indication("in Workspace",11, 16);
 
-    // Inform on link
-    ImGui::SetCursorPos( ImVec2(preview_width + 20, pos.y + 2.1f * ImGui::GetFrameHeightWithSpacing()) );
-    if (s.mixingGroup() != nullptr) {
-        if (ImGuiToolkit::IconButton(ICON_FA_LINK, "Linked")){
-            Mixer::selection().clear();
-            Mixer::selection().add( s.mixingGroup()->getCopy() );
-        }
-    }
-    else
-        ImGuiToolkit::Indication("not Linked", ICON_FA_UNLINK);
-
-    // locking
-    ImGui::SetCursorPos( ImVec2(preview_width + 20, pos.y + 3.f * ImGui::GetFrameHeightWithSpacing()) );
-    const char *tooltip[2] = {"Unlocked", "Locked"};
-    bool l = s.locked();
-    if (ImGuiToolkit::IconToggle(15,6,17,6, &l, tooltip ) ) {
-        s.setLocked(l);
-        if (l) {
-            Mixer::selection().clear();
-            Action::manager().store(s.name() + std::string(": lock."));
-        }
-        else {
-            Mixer::selection().set(&s);
-            Action::manager().store(s.name() + std::string(": unlock."));
-        }
-    }
-
-    // Filter
-    bool on = s.imageProcessingEnabled();
-    ImGui::SetCursorPos( ImVec2( pos.x, pos.y + preview_height));
-    if (on)
-        ImGui::Text(ICON_FA_PALETTE "  Color correction");
-    else
-        ImGuiToolkit::Indication("Color correction filter is disabled", ICON_FA_PALETTE "  Color correction");
-    pos = ImGui::GetCursorPos();
-
-    // menu icon for image processing
-    ImGui::SameLine(preview_width, 2 * IMGUI_SAME_LINE);
-    if (ImGuiToolkit::IconButton(5, 8))
-        ImGui::OpenPopup( "MenuImageProcessing" );
-
-    if (ImGui::BeginPopup( "MenuImageProcessing" ))
-    {
-        if (ImGui::MenuItem("Enable", NULL, &on)) {
-            std::ostringstream oss;
-            oss << s.name() << ": " << ( on ? "Enable Color correction" : "Disable Color correction");
-            Action::manager().store(oss.str());
-            s.setImageProcessingEnabled(on);
-        }
-
-        if (s.processingshader_link_.connected()) {
-            if (ImGui::MenuItem( "Unfollow", NULL, false, on)){
-                s.processingshader_link_.disconnect();
+        // Inform on link
+        ImGui::SetCursorPos( ImVec2(preview_width + 20, pos.y + 2.1f * ImGui::GetFrameHeightWithSpacing()) );
+        if (s.mixingGroup() != nullptr) {
+            if (ImGuiToolkit::IconButton(ICON_FA_LINK, "Linked")){
+                Mixer::selection().clear();
+                Mixer::selection().add( s.mixingGroup()->getCopy() );
             }
         }
-        else {
-            if (ImGui::MenuItem("Reset", NULL, false, on )){
-                ImageProcessingShader defaultvalues;
-                s.processingShader()->copy(defaultvalues);
-                s.processingshader_link_.disconnect();
+        else
+            ImGuiToolkit::Indication("not Linked", ICON_FA_UNLINK);
+
+        // locking
+        ImGui::SetCursorPos( ImVec2(preview_width + 20, pos.y + 3.f * ImGui::GetFrameHeightWithSpacing()) );
+        const char *tooltip[2] = {"Unlocked", "Locked"};
+        bool l = s.locked();
+        if (ImGuiToolkit::IconToggle(15,6,17,6, &l, tooltip ) ) {
+            s.setLocked(l);
+            if (l) {
+                Mixer::selection().clear();
+                Action::manager().store(s.name() + std::string(": lock."));
+            }
+            else {
+                Mixer::selection().set(&s);
+                Action::manager().store(s.name() + std::string(": unlock."));
+            }
+        }
+
+        // Filter
+        bool on = s.imageProcessingEnabled();
+        ImGui::SetCursorPos( ImVec2( pos.x, pos.y + preview_height));
+        if (on)
+            ImGui::Text(ICON_FA_PALETTE "  Color correction");
+        else
+            ImGuiToolkit::Indication("Color correction filter is disabled", ICON_FA_PALETTE "  Color correction");
+        pos = ImGui::GetCursorPos();
+
+        // menu icon for image processing
+        ImGui::SameLine(preview_width, 2 * IMGUI_SAME_LINE);
+        if (ImGuiToolkit::IconButton(5, 8))
+            ImGui::OpenPopup( "MenuImageProcessing" );
+
+        if (ImGui::BeginPopup( "MenuImageProcessing" ))
+        {
+            if (ImGui::MenuItem("Enable", NULL, &on)) {
                 std::ostringstream oss;
-                oss << s.name() << ": " << "Reset Filter";
+                oss << s.name() << ": " << ( on ? "Enable Color correction" : "Disable Color correction");
                 Action::manager().store(oss.str());
+                s.setImageProcessingEnabled(on);
             }
-            if (ImGui::MenuItem("Copy", NULL, false, on )){
-                std::string clipboard = SessionVisitor::getClipboard(s.processingShader());
-                if (!clipboard.empty())
-                    ImGui::SetClipboardText(clipboard.c_str());
+
+            if (s.processingshader_link_.connected()) {
+                if (ImGui::MenuItem( "Unfollow", NULL, false, on)){
+                    s.processingshader_link_.disconnect();
+                }
             }
-            const char *clipboard = ImGui::GetClipboardText();
-            const bool can_paste = (clipboard != nullptr && SessionLoader::isClipboard(clipboard));
-            if (ImGui::MenuItem("Paste", NULL, false, can_paste)) {
-                SessionLoader::applyImageProcessing(s, clipboard);
-                std::ostringstream oss;
-                oss << s.name() << ": " << "Change Filter";
-                Action::manager().store(oss.str());
+            else {
+                if (ImGui::MenuItem("Reset", NULL, false, on )){
+                    ImageProcessingShader defaultvalues;
+                    s.processingShader()->copy(defaultvalues);
+                    s.processingshader_link_.disconnect();
+                    std::ostringstream oss;
+                    oss << s.name() << ": " << "Reset Filter";
+                    Action::manager().store(oss.str());
+                }
+                if (ImGui::MenuItem("Copy", NULL, false, on )){
+                    std::string clipboard = SessionVisitor::getClipboard(s.processingShader());
+                    if (!clipboard.empty())
+                        ImGui::SetClipboardText(clipboard.c_str());
+                }
+                const char *clipboard = ImGui::GetClipboardText();
+                const bool can_paste = (clipboard != nullptr && SessionLoader::isClipboard(clipboard));
+                if (ImGui::MenuItem("Paste", NULL, false, can_paste)) {
+                    SessionLoader::applyImageProcessing(s, clipboard);
+                    std::ostringstream oss;
+                    oss << s.name() << ": " << "Change Filter";
+                    Action::manager().store(oss.str());
+                }
+                //            // NON-stable style follow mechanism
+                //            ImGui::Separator();
+                //            if (ImGui::BeginMenu("Follow", on))
+                //            {
+                //                for (auto mpit = Mixer::manager().session()->begin();
+                //                     mpit != Mixer::manager().session()->end(); mpit++ )
+                //                {
+                //                    std::string label = (*mpit)->name();
+                //                    if ( (*mpit)->id() != s.id() &&
+                //                         (*mpit)->imageProcessingEnabled() &&
+                //                         !(*mpit)->processingshader_link_.connected()) {
+                //                        if (ImGui::MenuItem( label.c_str() )){
+                //                            s.processingshader_link_.connect(*mpit);
+                //                            s.touch();
+                //                        }
+                //                    }
+                //                }
+                //                ImGui::EndMenu();
+                //            }
             }
-//            // NON-stable style follow mechanism
-//            ImGui::Separator();
-//            if (ImGui::BeginMenu("Follow", on))
-//            {
-//                for (auto mpit = Mixer::manager().session()->begin();
-//                     mpit != Mixer::manager().session()->end(); mpit++ )
-//                {
-//                    std::string label = (*mpit)->name();
-//                    if ( (*mpit)->id() != s.id() &&
-//                         (*mpit)->imageProcessingEnabled() &&
-//                         !(*mpit)->processingshader_link_.connected()) {
-//                        if (ImGui::MenuItem( label.c_str() )){
-//                            s.processingshader_link_.connect(*mpit);
-//                            s.touch();
-//                        }
-//                    }
-//                }
-//                ImGui::EndMenu();
-//            }
+
+            ImGui::EndPopup();
         }
 
-        ImGui::EndPopup();
-    }
+        if (s.imageProcessingEnabled()) {
 
-    if (s.imageProcessingEnabled()) {
+            // full panel for image processing
+            ImGui::SetCursorPos( pos );
+            ImGui::Spacing();
+
+            if (s.processingshader_link_.connected()) {
+                Source *target = s.processingshader_link_.source();
+                ImGui::Text("Following");
+                if ( target != nullptr && ImGui::Button(target->name().c_str(), ImVec2(IMGUI_RIGHT_ALIGN, 0)) )
+                    Mixer::manager().setCurrentSource(target);
+            }
+            else
+                s.processingShader()->accept(*this);
+        }
 
-        // full panel for image processing
-        ImGui::SetCursorPos( pos );
         ImGui::Spacing();
 
-        if (s.processingshader_link_.connected()) {
-            Source *target = s.processingshader_link_.source();
-            ImGui::Text("Following");
-            if ( target != nullptr && ImGui::Button(target->name().c_str(), ImVec2(IMGUI_RIGHT_ALIGN, 0)) )
-                Mixer::manager().setCurrentSource(target);
-        }
-        else
-            s.processingShader()->accept(*this);
+        ImGui::PopID();
+
     }
+    else {
 
-    ImGui::Spacing();
+        // remember where we were...
+        ImVec2 pos = ImGui::GetCursorPos();
 
-    ImGui::PopID();
+        // preview (black texture)
+        float width = preview_width;
+        float height = s.frame()->projectionArea().y * width / ( s.frame()->projectionArea().x * s.frame()->aspectRatio());
+        if (height > preview_height - space) {
+            height = preview_height - space;
+            width = height * s.frame()->aspectRatio() * ( s.frame()->projectionArea().x / s.frame()->projectionArea().y);
+        }
+        // centered image
+        ImGui::SetCursorPos( ImVec2(pos.x + 0.5f * (preview_width-width), pos.y + 0.5f * (preview_height-height-space)) );
+        ImGui::Image((void*)(uintptr_t) s.frame()->texture(), ImVec2(width, height));
+
+        // centered icon of failed (skull)
+        ImGui::SetCursorPos( ImVec2(pos.x + (width  -ImGui::GetFrameHeightWithSpacing())* 0.5f ,
+                                    pos.y + (height -ImGui::GetFrameHeightWithSpacing()) * 0.5f) );
+        ImGuiToolkit::PushFont(ImGuiToolkit::FONT_LARGE);
+        ImGui::Text(ICON_FA_SKULL);
+        ImGui::PopFont();
+
+        // back
+        ImGui::SetCursorPos( ImVec2( pos.x, pos.y + preview_height));
+        ImGui::Spacing();
+    }
 
     ImGuiToolkit::Icon(s.icon().x, s.icon().y);
     ImGui::SameLine(0, IMGUI_SAME_LINE);
@@ -568,6 +602,14 @@ void ImGuiVisitor::visit (MediaSource& s)
 
     ImGui::SameLine(0, IMGUI_SAME_LINE);
     ImGui::Text("Folder");
+
+//    ImGui::SetNextItemWidth(IMGUI_RIGHT_ALIGN);
+//    if ( ImGui::Button("Replace") ) {
+
+//        s.setPath("/home/bh/Videos/iss.mov");
+//        Mixer::manager().recreateSource( Mixer::manager().findSource( s.id() ) );
+
+//    }
 }
 
 void ImGuiVisitor::visit (SessionFileSource& s)
diff --git a/src/Mixer.cpp b/src/Mixer.cpp
index 5533dde..41c5d73 100644
--- a/src/Mixer.cpp
+++ b/src/Mixer.cpp
@@ -204,22 +204,28 @@ void Mixer::update()
     // grab frames to recorders & streamers
     FrameGrabbing::manager().grabFrame(session_->frame());
 
-    // delete sources which failed update (one by one)
-    Source *failure = session()->failedSource();
-    if (failure != nullptr) {
-        // failed media: remove it from the list of imports
-        MediaSource *failedMedia = dynamic_cast<MediaSource *>(failure);
-        if (failedMedia != nullptr) {
-            Settings::application.recentImport.remove( failedMedia->path() );
+    // manage sources which failed update
+    SourceListUnique failures = session()->failedSources();
+    for(auto it = failures.begin(); it != failures.end(); ++it)  {
+        // if the failed source is still attached to the mixer
+        if ( attached( *it ) ) {
+            // special case of failed Render loopback :
+            // it fails when resolution change, and we can fix it by
+            // recreating it in the current session
+            RenderSource *failedRender = dynamic_cast<RenderSource *>(*it);
+            if (failedRender != nullptr) {
+                g_printerr("%s failed render \n", failedRender->initials());
+                // try to recreate the failed render source
+                if ( !recreateSource(failedRender) )
+                    // delete the source if could not
+                    deleteSource(failedRender);
+            }
+            // general case:
+            // detatch failed sources from the mixer
+            // (not deleted in the session; user can replace it)
+            else
+                detach( *it );
         }
-        // failed Render loopback: replace it with one matching the current session
-        RenderSource *failedRender = dynamic_cast<RenderSource *>(failure);
-        if (failedRender != nullptr) {
-            if ( recreateSource(failedRender) )
-                failure = nullptr; // prevent delete (already done in recreateSource)
-        }
-        // delete the source
-        deleteSource(failure);
     }
 
     // update views
@@ -477,36 +483,36 @@ void Mixer::insertSource(Source *s, View::Mode m)
 }
 
 
-bool Mixer::replaceSource(Source *from, Source *to)
+void Mixer::replaceSource(Source *previous, Source *s)
 {
-    if ( from == nullptr || to == nullptr)
-        return false;
+    if ( previous == nullptr || s == nullptr)
+        return ;
 
-    // rename
-    renameSource(to, from->name());
+    // remember name
+    std::string previous_name = previous->name();
 
-    // remove source Nodes from all views
-    detach(from);
+    // remove source Nodes of previous from all views
+    detach(previous);
 
     // copy all transforms
-    to->group(View::MIXING)->copyTransform( from->group(View::MIXING) );
-    to->group(View::GEOMETRY)->copyTransform( from->group(View::GEOMETRY) );
-    to->group(View::LAYER)->copyTransform( from->group(View::LAYER) );
-    to->group(View::TEXTURE)->copyTransform( from->group(View::TEXTURE) );
+    s->group(View::MIXING)->copyTransform( previous->group(View::MIXING) );
+    s->group(View::GEOMETRY)->copyTransform( previous->group(View::GEOMETRY) );
+    s->group(View::LAYER)->copyTransform( previous->group(View::LAYER) );
+    s->group(View::TEXTURE)->copyTransform( previous->group(View::TEXTURE) );
 
-    // TODO copy all filters
+    // apply image processing
+    SessionLoader loader( session_ );
+    loader.applyImageProcessing(*s, SessionVisitor::getClipboard(previous));
+    s->setImageProcessingEnabled( previous->imageProcessingEnabled() );
 
+    // delete previous source
+    session_->deleteSource(previous);
 
-    // add source Nodes to all views
-    attach(to);
+    // rename s
+    renameSource(s, previous_name);
 
-    // add source
-    session_->addSource(to);
-
-    // delete source
-    session_->deleteSource(from);
-
-    return true;
+    // add source s
+    candidate_sources_.push_back(s);
 }
 
 
@@ -517,15 +523,20 @@ bool Mixer::recreateSource(Source *s)
 
     // get the xml description from this source, and exit if not wellformed
     tinyxml2::XMLDocument xmlDoc;
-    tinyxml2::XMLElement* sourceNode = SessionLoader::firstSourceElement(SessionVisitor::getClipboard(s), xmlDoc);
+    std::string clip = SessionVisitor::getClipboard(s);
+    g_printerr("clibboard\n%s", clip.c_str());
+
+    tinyxml2::XMLElement* sourceNode = SessionLoader::firstSourceElement(clip, xmlDoc);
     if ( sourceNode == nullptr )
         return false;
 
     // actually create the source with SessionLoader using xml description
     SessionLoader loader( session_ );
     Source *replacement = loader.createSource(sourceNode, SessionLoader::DUPLICATE); // not clone
-    if (replacement == nullptr)
+    if (replacement == nullptr) {
+        g_printerr("replacement failed \n");
         return false;
+    }
 
     // remove source Nodes from all views
     detach(s);
@@ -588,7 +599,8 @@ void Mixer::detach(Source *s)
     if ( s != nullptr )
     {
         // in case it was the current source...
-        unsetCurrentSource();
+        if ( s == currentSource() )
+            unsetCurrentSource();
         // in case it was selected..
         selection().remove(s);
         // detach from views
@@ -600,7 +612,10 @@ void Mixer::detach(Source *s)
     }
 }
 
-
+bool Mixer::attached (Source *s) const
+{
+    return s->group(View::MIXING)->refcount_ > 0;
+}
 
 bool Mixer::concealed(Source *s)
 {
@@ -623,9 +638,8 @@ void Mixer::conceal(Source *s)
         // remove from session
         session_->removeSource(s);
 
-        // detach from scene workspace, and put only in mixing background
+        // detach from scene workspace
         detach(s);
-        mixing_.scene.bg()->attach( s->group(View::MIXING) );
     }
 }
 
@@ -635,7 +649,6 @@ void Mixer::uncover(Source *s)
     if ( it != stash_.end() ) {
         stash_.erase(it);
 
-        mixing_.scene.bg()->detach( s->group(View::MIXING) );
         attach(s);
         session_->addSource(s);
     }
diff --git a/src/Mixer.h b/src/Mixer.h
index 867316d..e924063 100644
--- a/src/Mixer.h
+++ b/src/Mixer.h
@@ -62,6 +62,7 @@ public:
     // operations on sources
     void addSource    (Source *s);
     void deleteSource (Source *s);
+    void replaceSource(Source *previous, Source *s);
     void renameSource (Source *s, const std::string &newname = "");
     int  numSource    () const;
 
@@ -139,10 +140,10 @@ protected:
     SourceList candidate_sources_;
     SourceList stash_;
     void insertSource  (Source *s, View::Mode m = View::INVALID);
-    bool replaceSource (Source *from, Source *to);
     bool recreateSource(Source *s);
     void attach        (Source *s);
     void detach        (Source *s);
+    bool attached      (Source *s) const;
 
     void setCurrentSource(SourceList::iterator it);
     SourceList::iterator current_source_;
diff --git a/src/MultiFileSource.cpp b/src/MultiFileSource.cpp
index 2416676..f7c0583 100644
--- a/src/MultiFileSource.cpp
+++ b/src/MultiFileSource.cpp
@@ -255,8 +255,7 @@ guint64 MultiFileSource::playtime () const
 void MultiFileSource::accept (Visitor& v)
 {
     Source::accept(v);
-    if (!failed())
-        v.visit(*this);
+    v.visit(*this);
 }
 
 MultiFile *MultiFileSource::multifile () const
diff --git a/src/NetworkSource.cpp b/src/NetworkSource.cpp
index 1e2d046..e0300ab 100644
--- a/src/NetworkSource.cpp
+++ b/src/NetworkSource.cpp
@@ -346,8 +346,7 @@ std::string NetworkSource::connection() const
 void NetworkSource::accept(Visitor& v)
 {
     Source::accept(v);
-    if (!failed())
-        v.visit(*this);
+    v.visit(*this);
 }
 
 glm::ivec2 NetworkSource::icon() const
diff --git a/src/PatternSource.cpp b/src/PatternSource.cpp
index fbd09df..43b9d2e 100644
--- a/src/PatternSource.cpp
+++ b/src/PatternSource.cpp
@@ -78,6 +78,8 @@ Pattern::Pattern() : Stream(), type_(UINT_MAX) // invalid pattern
 
 pattern_descriptor Pattern::get(uint type)
 {
+    type = CLAMP(type, 0, patterns_.size()-1);
+
     // check availability of feature to use this pattern
     if (!patterns_[type].available)
         patterns_[type].available = GstToolkit::has_feature(patterns_[type].feature);
@@ -164,8 +166,7 @@ void PatternSource::setPattern(uint type, glm::ivec2 resolution)
 void PatternSource::accept(Visitor& v)
 {
     Source::accept(v);
-    if (!failed())
-        v.visit(*this);
+    v.visit(*this);
 }
 
 Pattern *PatternSource::pattern() const
diff --git a/src/RenderSource.cpp b/src/RenderSource.cpp
index d6b8e25..72e2479 100644
--- a/src/RenderSource.cpp
+++ b/src/RenderSource.cpp
@@ -155,8 +155,7 @@ glm::vec3 RenderSource::resolution() const
 void RenderSource::accept(Visitor& v)
 {
     Source::accept(v);
-    if (!failed())
-        v.visit(*this);
+    v.visit(*this);
 }
 
 glm::ivec2 RenderSource::icon() const
diff --git a/src/Session.cpp b/src/Session.cpp
index ae48607..a8c58e3 100644
--- a/src/Session.cpp
+++ b/src/Session.cpp
@@ -46,7 +46,7 @@ SessionNote::SessionNote(const std::string &t, bool l, int s): label(std::to_str
 }
 
 Session::Session(uint64_t id) : id_(id), active_(true), activation_threshold_(MIXING_MIN_THRESHOLD),
-    filename_(""), failedSource_(nullptr), thumbnail_(nullptr)
+    filename_(""), thumbnail_(nullptr)
 {
     // create unique id
     if (id_ == 0)
@@ -179,7 +179,6 @@ void Session::update(float dt)
     }
 
     // pre-render all sources
-    failedSource_ = nullptr;
     bool ready = true;
     for( SourceList::iterator it = sources_.begin(); it != sources_.end(); ++it){
 
@@ -190,7 +189,9 @@ void Session::update(float dt)
 
         // discard failed source
         if ( (*it)->failed() ) {
-            failedSource_ = (*it);
+            // insert source in list of failed
+            // (NB: insert in set fails if source is already listed)
+            failed_.insert( *it );
         }
         // render normally
         else {
@@ -292,6 +293,8 @@ SourceList::iterator Session::deleteSource(Source *s)
         // inform group
         if (s->mixingGroup() != nullptr)
             s->mixingGroup()->detach(s);
+        // erase the source from the failed list
+        failed_.erase(s);
         // erase the source from the update list & get next element
         its = sources_.erase(its);
         // delete the source : safe now
@@ -321,6 +324,8 @@ SourceList::iterator Session::removeSource(Source *s)
         // inform group
         if (s->mixingGroup() != nullptr)
             s->mixingGroup()->detach(s);
+        // erase the source from the failed list
+        failed_.erase(s);
         // erase the source from the update list & get next element
         ret = sources_.erase(its);
     }
diff --git a/src/Session.h b/src/Session.h
index d748a9c..1870b8e 100644
--- a/src/Session.h
+++ b/src/Session.h
@@ -94,8 +94,8 @@ public:
     void setActive (bool on);
     inline bool active () { return active_; }
 
-    // return the last source which failed
-    Source *failedSource () { return failedSource_; }
+    // return the list of sources which failed
+    SourceListUnique failedSources () const { return failed_; }
 
     // get frame result of render
     inline FrameBuffer *frame () const { return render_.frame(); }
@@ -183,7 +183,7 @@ protected:
     float activation_threshold_;
     RenderView render_;
     std::string filename_;
-    Source *failedSource_;
+    SourceListUnique failed_;
     SourceList sources_;
     void validate(SourceList &sources);
     std::list<SessionNote> notes_;
diff --git a/src/SessionSource.cpp b/src/SessionSource.cpp
index ef890fc..2425164 100644
--- a/src/SessionSource.cpp
+++ b/src/SessionSource.cpp
@@ -153,9 +153,10 @@ void SessionSource::update(float dt)
         timer_ += guint64(dt * 1000.f) * GST_USECOND;
     }
 
-    // delete a source which failed
-    if (session_->failedSource() != nullptr) {
-        session_->deleteSource(session_->failedSource());
+    // delete source which failed
+    SourceListUnique::iterator failure = session_->failedSources().cbegin();
+    if ( failure != session_->failedSources().cend() ) {
+        session_->deleteSource( *failure );
         // fail session if all sources failed
         if ( session_->size() < 1)
             failed_ = true;
@@ -349,8 +350,7 @@ void SessionFileSource::render()
 void SessionFileSource::accept(Visitor& v)
 {
     Source::accept(v);
-    if (!failed())
-        v.visit(*this);
+    v.visit(*this);
 }
 
 glm::ivec2 SessionFileSource::icon() const
@@ -433,8 +433,7 @@ bool SessionGroupSource::import(Source *source)
 void SessionGroupSource::accept(Visitor& v)
 {
     Source::accept(v);
-    if (!failed())
-        v.visit(*this);
+    v.visit(*this);
 }
 
 glm::ivec2 SessionGroupSource::icon() const
diff --git a/src/SourceList.h b/src/SourceList.h
index 9ed3fc7..2ca28b1 100644
--- a/src/SourceList.h
+++ b/src/SourceList.h
@@ -2,6 +2,7 @@
 #define SOURCELIST_H
 
 #include <list>
+#include <set>
 #include <glm/glm.hpp>
 
 class Source;
@@ -10,6 +11,7 @@ class Session;
 
 typedef std::list<Source *> SourceList;
 typedef std::list<SourceCore *> SourceCoreList;
+typedef std::set<Source *> SourceListUnique;
 
 SourceList playable_only (const SourceList &list);
 SourceList valid_only    (const SourceList &list);
diff --git a/src/SrtReceiverSource.cpp b/src/SrtReceiverSource.cpp
index 385a84a..e25264d 100644
--- a/src/SrtReceiverSource.cpp
+++ b/src/SrtReceiverSource.cpp
@@ -50,8 +50,7 @@ std::string SrtReceiverSource::uri() const
 void SrtReceiverSource::accept(Visitor& v)
 {
     Source::accept(v);
-    if (!failed())
-        v.visit(*this);
+    v.visit(*this);
 }
 
 glm::ivec2 SrtReceiverSource::icon() const
diff --git a/src/StreamSource.cpp b/src/StreamSource.cpp
index 93361f7..c48c03f 100644
--- a/src/StreamSource.cpp
+++ b/src/StreamSource.cpp
@@ -71,8 +71,7 @@ std::list<std::string> GenericStreamSource::gstElements() const
 void GenericStreamSource::accept(Visitor& v)
 {
     Source::accept(v);
-    if (!failed())
-        v.visit(*this);
+    v.visit(*this);
 }
 
 glm::ivec2 GenericStreamSource::icon() const
diff --git a/src/UserInterfaceManager.cpp b/src/UserInterfaceManager.cpp
index 79257bd..12382f4 100644
--- a/src/UserInterfaceManager.cpp
+++ b/src/UserInterfaceManager.cpp
@@ -6179,6 +6179,8 @@ Navigator::Navigator()
     else
         new_media_mode = MEDIA_FOLDER;
     new_media_mode_changed = true;
+
+    source_to_replace = nullptr;
 }
 
 void Navigator::applyButtonSelection(int index)
@@ -6213,6 +6215,7 @@ void Navigator::clearButtonSelection()
 
     // clear new source pannel
     clearNewPannel();
+    source_to_replace = nullptr;
 }
 
 void Navigator::showPannelSource(int index)
@@ -6297,12 +6300,23 @@ void Navigator::Render()
             if (ImGui::IsItemHovered())
                 tooltip = {TOOLTIP_MAIN, SHORTCUT_MAIN};
 
+            //
             // the list of INITIALS for sources
+            //
             int index = 0;
             SourceList::iterator iter;
             for (iter = Mixer::manager().session()->begin(); iter != Mixer::manager().session()->end(); ++iter, ++index)
             {
                 Source *s = (*iter);
+
+                // ignore source if failed (managed in stash below)
+                if (s->failed()){
+                    ImGui::PushStyleColor(ImGuiCol_Text, ImVec4(1.f, 0.3f, 0.2f, 1.f));
+                    ImGui::PushStyleColor(ImGuiCol_Header, ImGui::GetColorU32(ImGuiCol_Button));
+                    ImGui::PushStyleColor(ImGuiCol_HeaderActive, ImGui::GetColorU32(ImGuiCol_ButtonActive));
+                    ImGui::PushStyleColor(ImGuiCol_HeaderHovered, ImGui::GetColorU32(ImGuiCol_ButtonHovered));
+                }
+
                 // draw an indicator for current source
                 if ( s->mode() >= Source::SELECTED ){
                     ImVec2 p1 = ImGui::GetCursorScreenPos() + ImVec2(icon_width, 0.5f * sourceiconsize.y);
@@ -6346,12 +6360,19 @@ void Navigator::Render()
                     ImGui::EndDragDropTarget();
                 }
 
+                if (s->failed()){
+                    ImGui::PopStyleColor(4);
+                }
+
                 ImGui::PopID();
             }
 
             // the "+" icon for action of creating new source
-            if (ImGui::Selectable( ICON_FA_PLUS, &selected_button[NAV_NEW], 0, iconsize))
+            if (ImGui::Selectable( source_to_replace != nullptr ? ICON_FA_PLUS_SQUARE : ICON_FA_PLUS,
+                                   &selected_button[NAV_NEW], 0, iconsize)) {
+                Mixer::manager().unsetCurrentSource();
                 applyButtonSelection(NAV_NEW);
+            }
             if (ImGui::IsItemHovered())
                 tooltip = {TOOLTIP_NEW_SOURCE, SHORTCUT_NEW_SOURCE};
         }
@@ -6539,14 +6560,48 @@ void Navigator::RenderSourcePannel(Source *s)
         if (ImGuiToolkit::InputText("Name", &sname) ){
             Mixer::manager().renameSource(s, sname);
         }
+
         // Source pannel
         static ImGuiVisitor v;
         s->accept(v);
-        // clone & delete buttons
         ImGui::Text(" ");
-        // Action on source
-        if ( ImGui::Button( ICON_FA_SHARE_SQUARE " Clone & Filter", ImVec2(ImGui::GetContentRegionAvail().x, 0)) )
+
+        // clone button
+        if ( s->failed() ) {
+            ImGuiToolkit::ButtonDisabled( ICON_FA_SHARE_SQUARE " Clone & Filter", ImVec2(ImGui::GetContentRegionAvail().x, 0));
+        }
+        else if ( ImGui::Button( ICON_FA_SHARE_SQUARE " Clone & Filter", ImVec2(ImGui::GetContentRegionAvail().x, 0)) )
             Mixer::manager().addSource ( Mixer::manager().createSourceClone() );
+
+        // replace button
+        if ( s->cloned() ) {
+            ImGuiToolkit::ButtonDisabled( ICON_FA_PLUS_SQUARE " Replace", ImVec2(ImGui::GetContentRegionAvail().x, 0));
+            if (ImGui::IsItemHovered())
+                ImGuiToolkit::ToolTip("Cannot replace if source is cloned");
+        }
+        else if ( ImGui::Button( ICON_FA_PLUS_SQUARE " Replace", ImVec2(ImGui::GetContentRegionAvail().x, 0)) ) {
+            // prepare panel for new source of same type
+            MediaSource *file = dynamic_cast<MediaSource *>(s);
+            MultiFileSource *sequence = dynamic_cast<MultiFileSource *>(s);
+            CloneSource *internal = dynamic_cast<CloneSource *>(s);
+            PatternSource *generated = dynamic_cast<PatternSource *>(s);
+            if (file != nullptr)
+                Settings::application.source.new_type = SOURCE_FILE;
+            else if (sequence != nullptr)
+                Settings::application.source.new_type = SOURCE_SEQUENCE;
+            else if (internal != nullptr)
+                Settings::application.source.new_type = SOURCE_INTERNAL;
+            else if (generated != nullptr)
+                Settings::application.source.new_type = SOURCE_GENERATED;
+            else
+                Settings::application.source.new_type = SOURCE_CONNECTED;
+
+            // switch to panel new source
+            showPannelSource(NAV_NEW);
+            // set source to be replaced
+            source_to_replace = s;
+        }
+        // delete button
         if ( ImGui::Button( ICON_FA_BACKSPACE " Delete", ImVec2(ImGui::GetContentRegionAvail().x, 0)) ) {
             Mixer::manager().deleteSource(s);
             Action::manager().store(sname + std::string(": deleted"));
@@ -6603,7 +6658,10 @@ void Navigator::RenderNewPannel()
         // TITLE
         ImGui::SetCursorPosY(10);
         ImGuiToolkit::PushFont(ImGuiToolkit::FONT_LARGE);
-        ImGui::Text("Insert");
+        if (source_to_replace != nullptr)
+            ImGui::Text("Replace");
+        else
+            ImGui::Text("Insert");
         ImGui::PopFont();
 
         // Edit menu
@@ -7200,11 +7258,14 @@ void Navigator::RenderNewPannel()
             new_source_preview_.Render(ImGui::GetContentRegionAvail().x IMGUI_RIGHT_ALIGN);
             // ask to import the source in the mixer
             ImGui::NewLine();
-            if (new_source_preview_.ready() && ImGui::Button( ICON_FA_CHECK "  Create", ImVec2(pannel_width_ - padding_width_, 0)) ) {
+            if (new_source_preview_.ready() && ImGui::Button( ICON_FA_CHECK "  Ok", ImVec2(pannel_width_ - padding_width_, 0)) ) {
                 // take out the source from the preview
                 Source *s = new_source_preview_.getSource();
                 // restart and add the source.
-                Mixer::manager().addSource(s);
+                if (source_to_replace != nullptr)
+                    Mixer::manager().replaceSource(source_to_replace, s);
+                else
+                    Mixer::manager().addSource(s);
                 s->replay();
                 // close NEW pannel
                 togglePannelNew();
diff --git a/src/UserInterfaceManager.h b/src/UserInterfaceManager.h
index b0e9297..40bf03e 100644
--- a/src/UserInterfaceManager.h
+++ b/src/UserInterfaceManager.h
@@ -209,6 +209,7 @@ private:
     std::string sourceMediaFileCurrent;
     MediaCreateMode new_media_mode;
     bool new_media_mode_changed;
+    Source *source_to_replace;
 };
 
 class ToolBox