This is for a variety of reasons.
Should this occur, you will still be able to see the video, but the audio will be muted. If you get a broken graphic or a cam with a red circle with a red slash in it, this means the video is NOT online at all. If this should occur, simply come back later and the cam should be back online.
One final thing, if the video stops, just simply hit REFRESH or RELOAD in your browser and this page will refresh itself.