Each image is a snapshot of the warp bubble at a given moment, which were then glued together to form the movie. For this simmulation, the bubble is travelling at the speed of light. The four second duration of the movie is in extreme slow motion. In reality, all of the images would flash by in under 1.2 millionths of a second. Although warp drive sounds appealing, it does have one serious drawback.
Negative energy comes about from special states of quantum field theory.
Some examples are highly squeezed states of light, the Casimir vacuum energy between two uncharged conducting plates and states which are superpositions of particle number. In all of these examples some region of space has negative energy density which is a violation of the classical energy conditions. However, since these are all quantum effects the classical energy conditions really can't be applied. Now you might be wondering why I may seem concerned about allowing negative energy to exist. First off, let me say what you could do if you could manipulate large amounts of negative energy.