Unzip it into Photoshop’s script folder (mine is C:\Program Files\Adobe\Adobe Photoshop CS5 (64 Bit)\Presets\Scripts, probably varies depending on version/OS.)
Open photoshop, then open an animated GIF, import a video, or take a still image in duplicate its layer a bunch of times– essentially, you need to have the frames as separate layers, starting from the bottom.
Click on File | Scripts, and “Animated Content Aware Scale” should be there. If not, you put the file in the wrong folder, but you can click “Browse” and find it manually.
This sexy options box will pop up. Basically, you can tween the drastic-ness of the scaling between the beginning and the ending of the clip. Smaller heights and widths generally make people look crunched and big-eyed. Bigger ones generally make people look pencil-headed and small-eyed.
Play around with these numbers for some weird effects, but be wary that extreme scaling can take a while to process (so don’t, say, put all four sliders all the way down to 1 on a 100-frame, hi-def animation. That will look terrible anyway.)
The “algorithm” option has three methods of scaling. The first two methods are similar, but can both result in really pixelated images depending on whether you’re scaling up or scaling down. The third method, “C.A Scale -> C.A Scale”, essentially content-aware-scales each frame twice, and thus takes longer, and has more unpredictable results.
After you click “Run” and it finishes processing, your finished product will be converted into a frame animation, so you can just hit space and watch it play, or export it as a GIF, or render it as a video, or delete it forever because it’s horrifying.
Note: If you have a lot of frames, your Undo History probably won’t go back far enough to undo the whole operation, so save first if it’s something you care about.