To upload a video, you'll need to host it on a service like youtube. It's free and you can host virtually unlimited (legal) content. From there, when you get a video, you can EMBED that video as a code in your instructable. Rationale: Video is HUGE. Instructables can't afford to host video content as the bandwidth cost would sink instructables. By keeping video off-site, they allow the free service to bear the cost.