Hi, try to install a MJPEG server in your Raspberry Pi (sure there are tutorials in the Internet for that). This will provide you with an URL that you can directly include in the widget. Hope it helps!
A DVR digitize the CCTV video signal both for live streaming and store the information in hard disk drives in a digital format. So, it is necessary to know the model and its features, to see if they can provide a standard MJPEG video signal. Then it would be necessary to include the URL in a dashboard.