A few moments after the video begins playing you may see it resize and thumbnails populate below the video. Thumbnails are only displayed when viewing a single channel and if the service has been enabled by your MIS administrator. With a recorded program you can use the thumbnail storyboard to quickly move forward and backward in time. With a live program, obviously, you are only able to move backward.
At the end of the seek interval the thumbnail is automatically updated to the next time increment.