Add PNG Animation to Keynote

I have a sequence of PNG files. I put them into PNG Animator app. The pictures animated in the app, I exported the file to my desktop. The animation will play when the file is dropped into Firefox; however, when I drop the file into Keynote, I just see the first frame and no animation. Keynote shows the file as a PNG file.

How can I take a series of PNG photos with a transparent background, create an animation file, and use it in Keynote? Your thoughts will be appreciated.

Mike