Hi MIROFSOFT, you right, it is perhaps the best movie made on this period.
The director was
Pierre Schœndœrffer.
He was in DBP as reporter for the French Army and was also made prisonner by the Viet Minh.
He lost all he had filmed during the battle, and nobody know where are the fims.
He also made other film about French Army:
Le Crabe-Tambour (quite good as the 317° section)
L'honneur d'un Capitaine (about french war in Algeria-highly recommended)
Dien bien Phu (not a real good film)
View of the making of DBP, Pierre Schoendoerffer is the civil man in the center.
If you want sample of this film :
Pierre Schoendoerffer also make a really good documentary about American Vietnam War
The anderson Platoon,
Documentary where Schoendoerffer follow a section of the 1st Cavalry in 1966
If you want to see this documentary :
Highly recommended !