Ensure all color clips use the RGBA format

src/doc/kdenlivedoc.cpp

@@ -344,6 +344,7 @@ QDomDocument KdenliveDoc::createEmptyDocument(const QList<TrackInfo> &tracks)
     xmlConsumer.set("store", "kdenlive");
     Mlt::Tractor tractor(docProfile);
     Mlt::Producer bk(docProfile, "color:black");
+    bk.set("mlt_image_format", "rgba");
     tractor.insert_track(bk, 0);
     for (int i = 0; i < tracks.count(); ++i) {
         Mlt::Tractor track(docProfile);

src/monitor/glwidget.cpp

@@ -125,6 +125,7 @@ GLWidget::GLWidget(int id, QWidget *parent)
     m_refreshTimer.setSingleShot(true);
     m_refreshTimer.setInterval(10);
     m_blackClip.reset(new Mlt::Producer(pCore->getCurrentProfile()->profile(), "color:0"));
+    m_blackClip->set("mlt_image_format", "rgba");
     m_blackClip->set("kdenlive:id", "black");
     m_blackClip->set("out", 3);
     connect(&m_refreshTimer, &QTimer::timeout, this, &GLWidget::refresh);
@@ -934,7 +935,6 @@ int GLWidget::setProducer(const std::shared_ptr<Mlt::Producer> &producer, bool i
         // Reset markersModel
         rootContext()->setContextProperty("markersModel", nullptr);
     }
-    // redundant check. postcondition of above is m_producer != null
     m_producer->set_speed(0);
     m_proxy->setSpeed(0);
     error = reconfigure();
@@ -1256,6 +1256,7 @@ void GLWidget::reloadProfile()
     }
     m_blackClip.reset(new Mlt::Producer(pCore->getCurrentProfile()->profile(), "color:0"));
     m_blackClip->set("kdenlive:id", "black");
+    m_blackClip->set("mlt_image_format", "rgba");
     if (existingConsumer) {
         reconfigure();
     }

src/monitor/monitor.cpp

@@ -699,6 +699,7 @@ void Monitor::buildBackgroundedProducer(int pos) {
         int maxLength = m_controller->originalProducer()->get_length();
         bg->set("length", maxLength);
         bg->set("out", maxLength - 1);
+        bg->set("mlt_image_format", "rgba");
         trac.set_track(*bg.get(), 0);
         trac.set_track(*m_controller->originalProducer().get(), 1);
         QString composite = TransitionsRepository::get()->getCompositingTransition();

src/timeline2/view/timelinecontroller.cpp

@@ -2215,6 +2215,7 @@ bool TimelineController::requestStartTrimmingMode(int mainClipId, bool addToSele
     std::shared_ptr<Mlt::Producer> black(new Mlt::Producer(*m_model->m_tractor->profile(), "color:black"));
     black->set("length", previewLength);
     black->set_in_and_out(0, previewLength);
+    black->set("mlt_image_format", "rgba");
     trac.set_track(*black.get(), 0);
     //trac.set_track( 1);