How to make a loop effect with video (example link inside)

[lakeviews]

I want to create something like this:

http://accessories.us.dell.com/sna/p...9&sku=222-7175

I know how to place the movie clip and everything but how does this clip work... It looks like it's continuously moving without a stopping point. How would I go about to creating something like this?

[silentweed]

most likely its just the end frame and the start frame of the animation are exactly the same - hence the loop is seamless