AFP determined the video was genuine through a digital investigation that included matching screenshots of the mosque taken from the gunman's footage with images available online showing the same areas.
The "manifesto" detailing motivations for the attack was posted on Friday morning onto a Twitter account with the same name and profile image as the Facebook page that streamed the attack.
In the video, the shooter parks his car next to the mosque and gets out of the vehicle with a rifle. He slowly goes to the boot of his car and retrieves another firearm.
He then walks into the compound of the mosque and fires at a person standing near the doorway before dropping the rifle and shooting repeatedly with the second weapon as he moves inside.
The gunman fires dozens of bullets at people trying to run away or lying down in huddled groups in corners of the rooms.
In the excerpt of the video viewed by AFP, which did not appear to be the full clip, he can be seen changing cartridges three times in just under two minutes.
The framing of the video, which shows only the gunman's hands holding the gun as he shoots and reloads, is eerily similar to the style of a first-person shooter video game.
AFP is not publishing the footage.