Essentially the process is to extract a subset of frames from the movie, then reduce the frames to one pixel wide. This causes the most prevalent colors of the film to stand out.

I'd really like to see the same treatment for videogames, I've been meaning to try the process on some videogame speedrun videos. Watching the evolution of color through a series like Mario could be pretty neat. Comparing Half Life's color palette to, say, Quake's would be interesting as well.