The first musical number in the film, ‘The Sound of Music’, was the final sequence shot in Europe before the cast and crew returned to Los Angeles. It was filmed in late June and early July of 1964. Despite the warm and sunny appearance, Julie Andrews notes that she was freezing running up that mountain over and over again. Director Robert Wise has said that he had to climb one of the trees nearby to be able to overview the helicopter shoot without getting in the picture.
During the filming of the opening shot of Andrews taken from a helicopter, she relates that although she tried digging her heels into the ground and bracing herself, on every take she was knocked over by the powerful helicopter downdraft. After more than a dozen takes, she attempted to hand-signal to Robert Wise to have the helicopter make a wider pass, but the response she got was a thumbs-up – he was finally satisfied with the shot.
Julie Andrews nearly turned down the role of Maria Von Trapp, fearing the character was too similar to her role in Mary Poppins (1964).
Andrews was always Wise’s first choice to play Maria even though no one had really seen how she worked onscreen. Mary Poppins hadn’t been released at that stage. Andrews sang “Supercalifragilisticexpialidocious” to the children in the cast to entertain them between shooting. Since Mary Poppins hadn’t yet been released, they just thought she’d made up the song for them.
The film’s status as the most successful movie musical was surpassed thirteen years later by Grease (1978) in actual box office collected, but this film remained the most successful movie musical when adjusted for inflation.
Marni Nixon had become well known in Hollywood circles as a ghost singer for the leads in several film adaptations of hit Broadway musicals. She provided the vocals for Deborah Kerr in The King and I (1956), Natalie Wood in West Side Story (1961) and Audrey Hepburn in My Fair Lady (1964). “The Sound of Music” provided a rare onscreen performance by Nixon, who plays Sister Sophia. Julie Andrews had previously appeared on Broadway in My Fair Lady (1964) but was passed over for the film. The producers were wary of how Andrews would react to Nixon because she dubbed Audrey Hepburn’s vocals in a role made famous by Andrews. When Andrews first met Nixon, she exclaimed, “Marni, I’m a fan of you!” and the producers were relieved. – Edited from IMDB