Fix audio mixer balance cannot be changed after project opening

Related to #559

src/audiomixer/mixerwidget.cpp

@@ -243,6 +243,7 @@ void MixerWidget::buildUI(Mlt::Tractor *service, const QString &trackTag)
             emit muteTrack(m_tid, !active);
             reset();
         }
+        pCore->setDocumentModified();
         updateLabel();
     });
 
@@ -306,6 +307,7 @@ void MixerWidget::buildUI(Mlt::Tractor *service, const QString &trackTag)
             m_levelFilter->set("disable", value == 60 ? 1 : 0);
             m_levels.clear();
             m_manager->purgeCache();
+            pCore->setDocumentModified();
         }
     });
     connect(m_balanceSpin, static_cast<void (QSpinBox::*)(int)>(&QSpinBox::valueChanged), [&](int value) {
@@ -316,6 +318,7 @@ void MixerWidget::buildUI(Mlt::Tractor *service, const QString &trackTag)
             m_balanceFilter->set("disable", value == 0 ? 1 : 0);
             m_levels.clear();
             m_manager->purgeCache();
+            pCore->setDocumentModified();
         }
     });
     QVBoxLayout *lay = new QVBoxLayout;

src/core.cpp

@@ -576,6 +576,11 @@ KdenliveDoc *Core::currentDoc()
     return m_projectManager->current();
 }
 
+void Core::setDocumentModified()
+{
+    m_projectManager->current()->setModified();;
+}
+
 int Core::projectDuration() const
 {
     if (!m_guiConstructed) {

src/core.h

@@ -93,6 +93,8 @@ public:
     ProjectManager *projectManager();
     /** @brief Returns a pointer to the current project. */
     KdenliveDoc *currentDoc();
+    /** @brief Set current project modified. */
+    void setDocumentModified();
     /** @brief Returns a pointer to the monitor manager. */
     MonitorManager *monitorManager();
     /** @brief Returns a pointer to the view of the project bin. */

src/timeline2/model/timelineitemmodel.cpp

@@ -470,6 +470,17 @@ void TimelineItemModel::setTrackStackEnabled(int tid, bool enable)
 void TimelineItemModel::importTrackEffects(int tid, std::weak_ptr<Mlt::Service> service)
 {
     std::shared_ptr<TrackModel> track = getTrackById(tid);
+    std::shared_ptr<Mlt::Tractor> destination = track->getTrackService();
+    // Audio mixer effects are attached to the Tractor service, while track effects are attached to first playlist service 
+    if (auto ptr = service.lock()) {
+        for (int i = 0; i < ptr->filter_count(); i++) {
+            std::unique_ptr<Mlt::Filter> filter(ptr->filter(i));
+            if (filter->get_int("internal_added") > 0) {
+                destination->attach(*filter.get());
+            }
+        }
+    }
+
     track->importEffects(std::move(service));
 }