I want to make a video Player with overlay and save this video

Question

I want to build a widget like facebook create story, want save video with text or any widget. This text or widget is movable and when save it the text or widget should be stay right position where user move text or widget.

 Stack(
    children: [
      Center(
        child: _controller.value.isInitialized
            ? AspectRatio(
                aspectRatio: _controller.value.aspectRatio,
                child: VideoPlayer(_controller),
              )
            : CircularProgressIndicator(),
      ),
      Positioned(
        left: _widgetPositionX,
        top: _widgetPositionY,
        child: Container(

          width: 100,
          height: 100,
          color:Colors.black
        ),
      ),
    ],
  ),

I want this save video with this widget and position