If it is the same format as the video interview used for last year's cadet programme, you get around 6 questions.
You see a person asking you a pre recorded question, you then get 30 seconds to come up with an answer, and then the software automatically starts recording through your webcam and gives you around 90 seconds to answer. It then moves onto the next question.
All a bit surreal, but try to treat it like a real interview (suit, tie etc), and take the time to set up a good 'studio' with the correct lighting, no interruptions...
Good luck all