Music by Prudence

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Music by Prudence was the official Oscar winner of the best documentary. Williams just run to the stage after hearing that.
Read more information from the article of lehighvalleylive.com:

Williams raced to the stage after "Music by Prudence" was announced as the Oscar winner. Shockingly he said, "It’s amazing. It feels great. It feels wonderful. It feels like an incredible milestone in my career and my life."
Read some more from an excellent article of lehighvalleylive.com:

The film was nominated for an Academy Award in the documentary short category.
"Music by Prudence" documents Mabhena's life. She's a 21-year-old from Zimbabwe who has arthrogryposis, a congenital disorder that crippled her arms and legs. She is a musician who leads a marimba band.
This is the first Academy Award for Williams, a filmmaker who now lives in New York and is a 1983 graduate of Northampton Community College.
During Williams' acceptance speech, he was interrupted by Elinor Burkett, who also was involved in making the film.