The most problematic issue in playing movies is the speed setting. If the movie tries to move through images too quickly, frames will be dropped or appear blank. Be sure to select a proper connection speed when first loading images. After the first pass through the images, they should reside in your browser's cache. At this point, you may greatly increase the speed of the movie for additional loops through the images. [Note: there are reasons the images were not set-up to "pre-load". This allows the tool to be used more easily off-line (say, with images on a CD), and allows the viewer to be a bit more responsive to user commands.]
The grey/red "LEDs" below the image are active LEDs. If you click on an LED, you go to that relative position in the image sequence. This works whether or not the movie is running.