Well what I do is find a theme, then work around it. For instance, lose weight, I can easily find a slew of before and after pictures, speak quickly about the benefits of losing weight and achieving a hard, sexy body. Of course that is set to music, watermarked, etc.
You can very easily make a free 30 second spot at Animoto, just find the pictures, upload and your done.
What I offer is more than that, since I'm a commercial account holder. I'll still start the process at Animoto, then download and add a bit to it with Vegas Video.
You can do the same with Windowns Movie Maker.
Then use Tubemogul for distribution, which easily gives you the ability to distribute video to multiple sites.
So in my opinion, and especially since you speak of a 20 second vid, then go signup and create a freebie at Animot.