Boko Haram remains a charged issue politically in Nigeria, where the government has failed to defeat the militants who have waged an insurgency since 2009 to carve out an Islamic state.
About 100 Chibok girls are unaccounted for, while thousands of other abducted children are still missing, campaigners say.
One diary entry given to the filmmakers described three girls who fled but were caught, flogged and thrown into a hole.
“They told us whosoever cries or begs for them not to be slaughtered will be slaughtered along with them,” a girl wrote.
A survivor named Habiba tells of being captured aged 15, locked in a cage for four months, and forced to marry a soldier.
She escaped, two months pregnant, and was caring for her baby and two orphans, boys kidnapped by Boko Haram to be child soldiers, when the filmmakers found them begging in the streets.