In MainMenuGui:

   new GuiButtonCtrl() {
      canSaveDynamicFields = "0";
      Profile = "GuiButtonProfile";
      HorizSizing = "left";
      VertSizing = "top";
      position = "712 509";
      Extent = "73 20";
      MinExtent = "8 8";
      canSave = "1";
      Visible = "1";
      Command = "loadIntroVideo();";
      hovertime = "1000";
      offset = "10 10";
      text = "Button title";
      groupNum = "-1";
      buttonType = "PushButton";
   };

Some script:

function loadIntroVideo()
{
   alxStop($musicHandle);
   exec("gamebase/client/ui/video_guis/VideoTest.gui");
   Canvas.pushDialog("VideoTest");
   theo.setFile("gamebase/data/video/lets_dance.ogg");
}

function stopIntroVideo()
{
   theo.stop();
   Canvas.popDialog("VideoTest");
  loadMainMenu();
}

VideoTest.gui:

//--- OBJECT WRITE BEGIN ---
new GuiControl(VideoTest) {
   canSaveDynamicFields = "0";
   Profile = "GuiDefaultProfile";
   HorizSizing = "right";
   VertSizing = "bottom";
   Position = "0 0";
   Extent = "800 600";
   MinExtent = "8 2";
   canSave = "1";
   Visible = "1";
   hovertime = "1000";
   CloseCommand = "stopIntroVideo();";
   

   new GuiButtonCtrl(VideoTestButton) {
      canSaveDynamicFields = "0";
      Profile = "GuiButtonProfile";
      HorizSizing = "right";
      VertSizing = "top";
      Position = "29 285";
      Extent = "110 20";
      MinExtent = "8 8";
      canSave = "1";
      Visible = "1";
      Command = "stopIntroVideo();";
      hovertime = "1000";
      text = "Stop that shit!";
      groupNum = "-1";
      buttonType = "PushButton";
	  accelerator = "escape";
   };
   new GuiTheoraCtrl(theo) {
      canSaveDynamicFields = "0";
      Profile = "GuiDefaultProfile";
      HorizSizing = "right";
      VertSizing = "bottom";
      Position = "169 81";
      Extent = "600 450";
      MinExtent = "8 2";
      canSave = "1";
      Visible = "1";
      hovertime = "1000";
      done = "0";
      stopOnSleep = "0";
      backgroundColor = "0 0 0 255";
   };
};
//--- OBJECT WRITE END ---