The 32-year-old Murphy died in 2009 of pneumonia, anemia and multiple drug intoxication.
Asked if Murphy had ever been signed to reprise her role from the first movie, Miller told UPI in a recent phone interview, "No, she wasn't."
"P!nk sang on the opening credits of the first movie with k.d. lang. She only sang for a while, but she came to visit on the set during that and I knew her and really liked her work. But then Brittany wasn't attached. She was wonderful, but very fragile and was already in quite a bit of trouble on the first film, so when Brittany died so sadly, P!nk had never really acted before, but I knew her just from our brief meetings for the first song and listening to her sing and talking about it and I said, 'Would you like to have a shot at this?' And she did," Miller explained. "She was under no illusions. She said, 'Well, I'm not really an actor.' And I told her: 'If you can sing like that, you clearly have to be an actor. It's just a question of shifting your technique.'"
Miller said the music star came into the studio the night before she was to start work on "Happy Feet Two," and observed Pitt and Matt Damon recording their lines as new characters Will and Bill the krill.
"I happened to have them do a little bit of singing and Matt Damon really could sing really well, but Brad Pitt is a terrible singer. But he was wonderful because he had no problem singing really badly in front of a really great singer," Miller recalled. "It really put her at her ease and she came in the next day and said: 'Well, I'll just let it go. ... If Brad's prepared to make such a fool out of himself, well, I'll give it a shot.' And she was much more comfortable. She's really good. She doesn't have a dishonest bone in her body, so everything she does is very honest and in this she has three big songs to sing."
Miller said he started developing the idea for the sequel to "Happy Feet" before he even finished working on the original movie.
"In the last few months of 'Happy Feet One,' I had lived with these characters for so long, they were like part of my imaginary family and so I almost had the second story worked out. It had evolved in my head," said Miller, who co-wrote the second film with Gary Eck.
The sequel follows the adventures of Erik, the young, performance-shy son of penguin pair Gloria, a fantastic singer, and Mumble, an incredible dancer, as he struggles to fit in amongst his peers in Antarctica. Erik sets out on an adventure with two of his pals and meets the Mighty Sven, a charismatic character who claims he is the only penguin who can fly. After an avalanche traps Erik's penguin community in an icy valley, Sven is asked to help teach the other penguins how to fly to safety; however, it soon becomes apparent Sven is not what he says he is. Erik's father then enlists the help of numerous different groups of animals to save their friends and neighbors, teaching Erik what true heroism is.
Elijah Wood once again lends his voice to Mumble, while newcomer Ava Acres plays Erik. The voice cast also includes Robin Williams, Hank Azaria, Sofia Vergara, Common, Hugo Weaving, Richard Carter, Magda Szubanski, Anthony LaPaglia and Benjamin "Lil P-Nut" Flores Jr.
"We wanted actors who really love working with other actors, so we made a point of bringing them all together when they're playing a scene. Of putting them in the same room," Miller noted. "Normally, in animation, they're in isolated booths. And, in this case, they were all working with each other, looking at each other and it made for so much more interesting and richer material because they could improvise. When you have someone like Hank Azaria and Robin Williams and Elijah Wood in the room, they're really working off each other. Or you have Robin Williams and Sofia Vergara doing a love scene, you put them in the same room, something better happens than you might normally get if you're just [taping] them by themselves."
Miller said the performances of Pitt and Damon, for example, were all the more hilarious because the actors are real-life friends who have previously acted together in several movies.
"When they had a few days available in the same city in between movies, we would get them together and it was so much better than it would have been if they were separate," the filmmaker said. "It was a very rich experience, working with all these people."
So, might audiences look forward to a "Happy Feet Three" somewhere on the horizon?
"Before I finished the first one, I already had a fairly decent idea of the story of 'Happy Feet Two,' but just having finished ... 'Happy Feet Two,' I wouldn't have any idea of how to approach 'Happy Feet Three.' Nothing has come to me at all. A lot of people have suggested doing a spin-off with the krill, but it needs penguins," Miller laughed.
Available in 3D and traditional 2D formats, "Happy Feet Two" is in theaters now.