It's a clip of a Tinkerbell movie before the final animation. The scene is made up with crudely drawn picture that convey the general idea of what it's going to look like when they finally animate it. It's got all the audio and dialogue, just not the full-fledged 3d animation. Basically, in the end of the video, all of Tink's friends sacrifice themselves for her after a dramatic scene where all hope seemed lost.