Coff,
Perhaps I can help.
Yes, it goes 'up and down'. It's been doing that for some while, this was another step in the clearance programme from basic to operational flight clearances.
The aircraft transitions from pure jet borne (zero knots airborne) to pure wing borne flight (a lot faster) through a 'transition envelope' that reduces jet thrust as wing lift increases. As it does that, the lift fan intake door 'schedules' from the fully open position you see in that clip (about 80 degrees) down to a lower setting (around 30 degrees), which is maintained until the aircraft is ready to come off jet thrust altogether and shut down the lift fan. The door operation is fully automatic, as are almost all of the aircraft systems involved in executing the transition.
The lift fan intake door design was a major challenge, as the 'bi-fold' system used on the X-35 had some major drawbacks that appeared in flight test. The door needs to be able to allow maximum airflow into the fan in a variety of conditions, from the hover (from all directions without generating unwanted intake vortices) to around 250 knots, getting the air to execute a quick 90 degree turn down into the lift fan, again without excessive intake distortion. The solution was a team effort, but special mention goes to some very talented Brits who came up with the solution.
Sorry you think it's ugly - for my own part, I just see a beautiful solution to a tough problem.
Best Regards as ever to those doing their best to deliver the goods
Engines