At least on the site liked in the OP they are sprite maps* saved in gif format not animated gifs. For example: http://www.animatedengines.com/jets.html http://

At least on the site liked in the OP they are sprite maps* saved in gif format not animated gifs. For example: http://www.animatedengines.com/jets.html http://www.animatedengines.com/jets.html The custom player takes the class of the div container (http://www.animatedengines.com/img/tprop_fl.gif http://www.animatedengines.com/img/tprop_fl.gif) "aeplayer aepframes_6" to determine the number of frames (6) and offsets the background-position vertically for each frame by the amount of the individual frame height which equals the div container height, thus appearing animated. *see this example with a sprite map in png format http://jsfiddle.net/simurai/CGmCe/ http://jsfiddle.net/simurai/CGmCe/