Demain dès l'aube (2009)

Thanks to a French speaking friend for letting me know about this French film which explores the world of reenacting in a darker way than say 'Faintheart'

Imdb says
Just saw this one at the Göteborg International Filmfestival. It was my opening film, and considering the talent, I expected something quality, and I got it. Vincent Perez plays a concert pianist, Mathieu, who takes a break from his good, but perhaps complicated life, to offer support to his brother Paul (Jeremie Renier), who lives with their very sick mother. Paul is into reenacting historical battles from the Napoleonic era, and Mathieu is sucked into this fantasy world, to stand by his brother. It turns out that the fantasy is more real than he had bargained for, and things get serious when people are easily offended, while playing the game. I'm not about to give the whole story away, but besides the interesting plot and excellent acting, there is also beautiful piano music and fantastic dueling scenes at dawn with great light. So go see, I'm glad I did!