UI: frontend api "trans. duration changed" event

UI/obs-frontend-api/obs-frontend-api.h

@@ -47,6 +47,8 @@ enum obs_frontend_event {
 
 	OBS_FRONTEND_EVENT_RECORDING_PAUSED,
 	OBS_FRONTEND_EVENT_RECORDING_UNPAUSED,
+
+	OBS_FRONTEND_EVENT_TRANSITION_DURATION_CHANGED,
 };
 
 /* ------------------------------------------------------------------------- */

UI/window-basic-main-transitions.cpp

@@ -616,6 +616,15 @@ void OBSBasic::on_transitionProps_clicked()
 	menu.exec(QCursor::pos());
 }
 
+void OBSBasic::on_transitionDuration_valueChanged(int value)
+{
+	if (api) {
+		api->on_event(OBS_FRONTEND_EVENT_TRANSITION_DURATION_CHANGED);
+	}
+
+	UNUSED_PARAMETER(value);
+}
+
 QuickTransition *OBSBasic::GetQuickTransition(int id)
 {
 	for (QuickTransition &qt : quickTransitions) {

UI/window-basic-main.hpp

@@ -788,6 +788,7 @@ private slots:
 	void on_transitionAdd_clicked();
 	void on_transitionRemove_clicked();
 	void on_transitionProps_clicked();
+	void on_transitionDuration_valueChanged(int value);
 
 	void on_modeSwitch_clicked();