When I upload my post with an animated .gif, the thumbnail generates into a new image and doesn't stay animated. It will stay animated inside the post which is great. It seems to resize the .gif image and convert it into a static image because it generates an image with the sizing at the end of the original file. Is there a code to add or remove that prevents it from generating a new image for the thumbnail so it just resizes down as the gif?
Actually WordPress render uploaded images. So if you upload a animated gif then it will not stay animated. Read this article on how to overcome these issue.
I haven't read it through but as Howdy_McGee said, you will have to use a plugin for that.