The good old animated Gif is a cool format again. It works on everything, no Flash or HTML5 video needed. You can handle it as simple as a static image... or not? By default the majority of Drupal installs are using GD to create thumbnails (image styles). But the stock PHP GD extension (coming with mod_php) lacks the functionality of properly handling animGifs and your mainpage or lister pages will remain static and boring.