The group’s leader, Abubakar Shekau, said the girls would be held until all imprisoned militants had been freed.
He said the girls had converted to Islam. The video, released on Monday, showed them praying.
Boko Haram abducted more than 200 girls from Chibok on April 14 and threatened to sell them.
The BBC reports that Boko Haram’s comments showed signs that the group was willing to negotiate.
Three of the girls are shown speaking in the 17-minute video, obtained by French news agency AFP, wearing the full-length hijab.
Two girls said they were Christian and have converted to Islam, while the other said she is Muslim.
“These girls, these girls you occupy yourselves with… we have indeed liberated them. These girls have become Muslims,” Abubakar Shekau said in the video.
It is thought the majority of the abducted girls are Christians, although there are a number of Muslims among them.
The BBC reports the girls appeared calm and one said that they had not been harmed.
There is no indication of when or where the video was taken.
It is estimated to show about 130 girls – just under half of the 276 pupils abducted from their school in Borno State.