Image not cleared when switching between different resolution videos

Hi,
I am using some video applications based on Gstreamer having different resolutions.I am embedding these applications and playing one at a time on a Qtwidget, but when i switch between any two applications having different resolutions the previous image is not cleared and the second is playing on top of other and if the second video is of less resolution then i can see the previous video image.

Please provide some suggestions on what to clear to stop this problem. I dont have have much idea of gstreamer and i cannot control this in Qt Side because i cannot detect the change in video.

I am passing window Id to the application into which my video application will be embedded, is there any way to clear the window by using window Id.

Thanks in advance.