Brie Larson Pivoted to Video

“It’s so exhausting to spend so much time nit-picking within your own head every detail of what you’re going to say,” she said. “I needed to know that it was OK for me to do something that was silly or simple and it wouldn’t blow everything up, which sounds really absurd almost a year later.”

She treated vlogging like studying for a new project. “When I’m prepping for a role, it’s like getting a crush,” she said. “You want to think about them, you want to talk about them, and everywhere you go, it’s almost like you get magical signs because your whole world is this love.”

Part of her research involved video calling successful YouTubers to learn their secrets. In that first announcement video, there are moments where Ms. Larson matches each vlogger’s emotional temperature.

“People love living vicariously through YouTubers, they love it, it’s weird,” Kelly Stamps, a vlogger, says in the video. “Like if you just go through my comments, people are just saying, ‘I love just seeing you be yourself on camera.’ Be relatable by just being honest.”

On a Zoom call in April, Ms. Larson tied up her damp hair and fixed the collar of her tartan Batsheva smock dress. She had just emerged from the sauna and ice bath, recovering from a training session for “Captain Marvel 2.” Sometimes, she vlogs her workouts with her trainer, Jason Walsh. “I just wanted to feel like in the human realm I could accomplish what she was doing in this superhero realm,” she said. “And it helped me inform the character. It didn’t make sense to just stand there and be like, ‘The C.G.I. will take care of this.’”

Over the years, Ms. Larson has learned how “plastic” her mind and body can be. “They can change for good and bad depending on what it is I’m doing,” she said. She has struggled mentally by playing characters like Joy Newsome in “Room” and Grace Howard in “Short Term 12,” but with Captain Marvel and Kit from “Unicorn Store,” her directorial debut, she felt herself embracing some character traits and taking them home with her.