In the video, the group alleged that the school girls had converted to Islam and would not be released until all militant prisoners were freed. The group's leader, Abubakar Shekau is seen speaking in the 17-minutes video, which shows the girls in Muslim dress and praying in an undisclosed rural location.
A total of 276 girls were abducted on April 14 from the northeastern town of Chibok, in Borno state, which has a sizeable Christian community. While a few girls managed to escape from the abductors, some 223 are still missing.
The group leader Shekau had earlier threatened to sell the girls as slaves
In the video, three of the girls are interviewed. Two say they were Christian and had converted while one said she was Muslim. The girls appeared calm and one said that they had not been harmed.
Boko Haram has been involved in violence in Nigeria's mainly Muslim north since 2009, attacking schools teaching a "Western" curriculum, churches and government targets.
The group leader Shekau had earlier threatened to sell the girls as slaves. Nigeria's government has been criticized for its lack of immediate response to the kidnapping. President Goodluck Jonathan has now accepted help from the United States, Britain, France, China and Israel, which have sent specialist teams to help in the search effort.
In the video, Shekau appears in front of a lime green canvas backdrop wearing combat fatigues and carrying an automatic weapon. In Hausa and Arabic, he says, "These girls, these girls you occupy yourselves with... we have indeed liberated them. We have indeed liberated them. Do you know we have liberated them? These girls have become Muslims".
"We will never release them (the girls) until after you release our brethren. Here I mean those girls who have not submitted (converted to Islam)," he added.