1. Search for the phrase fractal loop or fractal loop animation in youtube.com or youtube.jp To search with a phrase, I enclose them in quotes e.g. "fractal loop"
2. download the clip you've chosen.
3. convert the clip to mp4 to simplify things. My clip is called cherbloom.mp4 and runs for 7 seconds (small and lightweight is better).
4.As is, out of the box, terminology uses the vlc engine to playback mp4 (-ymmv)
5. cd to the directory where the converted clip is.
6. type the command terminology -b=cherbloom.mp4 and the clip will loop by itself.