The first officer says, "v1, rotate." V1 is the speed of no return which means the plane cannot stop and must continue to take off. The plane is not traveling fast enough to rotate and leave the ground at v1. Vr is the speed at which a plane can rotate and is much higher than v1.
The narrator goes on and on about whether the runway was long enough for the plane to get off the ground, but the plane DID get off the ground and then went out of control once in the air. Professional air traffic investigators would know that and not concern themselves with runway length. Weight would affect the ability of the plane to climb and stay aloft once in the air.