Oscar-winning director Lee Ang had no qualms casting rookie actor Joe Alwyn in the titular lead role of his new movie Billy Lynn's Long Halftime Walk.

"If a young actor is talented, I can sniff it out from 2 kilometers away. Within the first or second minute of an audition, I pretty much know," said Lee, who has helped to make stars of fresh faces such as Tang Wei in the espionage thriller Lust, Caution (2007).

He was speaking at a press event in Taipei on Thursday (Nov 3) for Billy Lynn, in which British newcomer Alwyn plays an American soldier hailed for his bravery in Iraq for rushing to his sergeant's aid under fire.

To prepare for the role, Alwyn, 25, reported for a tough bootcamp, one which approximated "70 per cent of Navy Seal training", said Lee.

Alwyn, who also attended the press event, had only had good things to say about his director: "I've always admired him for trying new things in all of his films and always pushing boundaries.

"At the same time, this was such new territory for me, it was definitely overwhelming."

The shoot was also overwhelming for another reason: There were a lot of close-ups of Alwyn's face.

He said: "The camera was only centimeters from my face but I didn't know the level of how intimate it was going to be. I didn't know the clarity and just how detailed it was going to be when you see right into somebody's eyes, right into someone's soul."

Lee's son, Mason, 26, who appears in the film as one of Billy's squadmates, had to experience the bootcamp as well.

The director said he was not worried about "torturing" his son. Instead, "I was more worried about others going through that training and I couldn't sleep well while they were at the training centre".

He probably also had technical matters on his mind - he took a risk on an unusual format and made the film at a high frame rate of 120 frames per second, at 4K resolution and in 3D.

The effect, he said, is to make someone watching the film feel as though he has gone through the exact journey as Billy, so that "you empathise deeply and you feel emotions more sharply".

Even though the Taiwan-born film-maker has been feted for much of his oeuvre, the two-time Oscar winner for Best Director (Brokeback Mountain, 2005; Life Of Pi, 2012) admitted he did not know if audiences will take to the groundbreaking format.

Ultimately, the format might not matter, because many cinemas, including those in Singapore, will be screening the movie in the regular format.

As Lee said: "In the end, it comes down to the movie's story, the performances and whether the content is moving - that's most important."

The film opens in Singapore on Nov 10.