Meryl Streep, who plays a witch in the new movie "Into the Woods," said she'd resisted similar roles in the past, but had a change of heart.

"I was offered three witches [roles] when I turned 40 - in one year," she told ABC News recently. "And I thought: 'Oh, this is how it's gonna go?' … At this point in my career, I think, I really think hard about: 'What am I putting into the world with each project?'"

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Streep said it was different when she was asked to appear in "Into the Woods," based on a musical by legendary composer Stephen Sondheim and due out Christmas Day.

Her real anxiety came from her desire to bring something new to the film.

"I was just up in my kitchen and just singing the karaoke version as, as much as I could, because I wanted to be ready," said Streep, whose opening song - a rap - was done entirely live.

The movie, directed by Rob Marshall, also features actors Anna Kendrick, Emma Blunt, James Corden and Chris Pine as well as Christine Baranski and Tracey Ullman.

"Into the Woods" is a Walt Disney Pictures production.

"You know when you're young and desperate, you just sort of jump into everything that you possibly can," Streep said. "But now, I really consider, 'Is this hurting or is this helping in some way?'"

Streep said Sondheim appeared on the set at times.

"First day, we were recording and he was there - Sondheim - unannounced and my song was first and Rob [Marshall] was somewhere and didn't tell me," Streep said. "But he was amazing. … The whole orchestra rose and applauded him."

She told ABC News she was "proud" of the movie, also a famous musical performed in many high schools across the US.

"It's a truthful thing and I feel like we served this great artist, Stephen Sondheim," she said. "We did serve him."

ABC News' Christine Romo contributed to this story.

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