I have seen this film and you should, too.
Jackson started with about 100 hours of contemporary (meaning, 100+ years old) silent, black-and-white 16 mm film, shot during the Great War on primitive cameras. He colorized it frame by frame with reality and sensitivity in mind, and then had lip-readers figure out what some of the characters were actually saying. He then used performers (from the same country) to speak those words, and added them to the video.
The result is extraordinary. It's as though Jackson took today's film technology and went back in time to make an on-location film of the War. The characters on the screen spring to life in a way that the herky-jerky old film never revealed.
If you're the least bit interested in military history, the Great War, or Britain and the Empire's role in it, you must see this film. And be sure to stay for the section by Jackson as to how they did it.
Simply amazing!