Create an UI file to design (and adjust) the widget more easily

src/gui/Timeline.cpp

 #include "Timeline.h"
 
-Timeline::Timeline()
+Timeline::Timeline(QWidget *parent) :
+    QWidget(parent){
+    m_ui.setupUi(this);
+}
+
+void Timeline::changeEvent(QEvent *e)
 {
+    switch (e->type()) {
+    case QEvent::LanguageChange:
+        m_ui.retranslateUi(this);
+        break;
+    default:
+        break;
+    }
 }

src/gui/Timeline.h

 #ifndef TIMELINE_H
 #define TIMELINE_H
 
-#include <QWidget>
+#include "ui_Timeline.h"
 
-class Timeline : public QWidget
-{
+class Timeline : public QWidget {
+    Q_OBJECT
+    Q_DISABLE_COPY(Timeline)
 public:
-    Timeline();
+    explicit Timeline(QWidget *parent = 0);
+
+protected:
+    virtual void changeEvent(QEvent *e);
+
+private:
+    Ui::Timeline m_ui;
 };
 
 #endif // TIMELINE_H

src/gui/ui/Timeline.ui

+<ui version="4.0" >
+ <author/>
+ <comment/>
+ <exportmacro/>
+ <class>Timeline</class>
+ <widget class="QWidget" name="Timeline" >
+  <property name="objectName" >
+   <string notr="true" >Form</string>
+  </property>
+  <property name="geometry" >
+   <rect>
+    <x>0</x>
+    <y>0</y>
+    <width>400</width>
+    <height>300</height>
+   </rect>
+  </property>
+  <property name="windowTitle" >
+   <string>Form</string>
+  </property>
+ </widget>
+ <pixmapfunction/>
+ <connections/>
+</ui>

vlmc.pro

@@ -8,23 +8,23 @@ QT += gui \
 SOURCES += src/main.cpp \
     src/gui/MainWindow.cpp \
     src/gui/LibraryWidget.cpp \
-    src/gui/Timeline.cpp \
     src/gui/DockWidgetManager.cpp \
     src/LibVLCpp/VLCException.cpp \
     src/LibVLCpp/VlmManager.cpp \
     src/LibVLCpp/VLCInstance.cpp \
-    src/LibVLCpp/VlmMedia.cpp
+    src/LibVLCpp/VlmMedia.cpp \
+    src/gui/Timeline.cpp
 HEADERS += src/gui/MainWindow.h \
     src/gui/DockWidgetManager.h \
     src/gui/LibraryWidget.h \
-    src/gui/Timeline.h \
     src/LibVLCpp/VLCpp.hpp \
     src/LibVLCpp/VLCException.h \
     src/LibVLCpp/VlmManager.h \
     src/LibVLCpp/VLCInstance.h \
-    src/LibVLCpp/VlmMedia.h
-
-FORMS += src/gui/ui/MainWindow.ui
+    src/LibVLCpp/VlmMedia.h \
+    src/gui/Timeline.h
+FORMS += src/gui/ui/MainWindow.ui \
+    src/gui/ui/Timeline.ui
 RESOURCES += 
 LIBS = -L/usr/local/lib \
     -lvlc