From the reading, I understand work is highly competitive, but the pool of workers willing to remain there indefinitely must be quite slim
It's more a case of no-one NEEDS to remain there indefinitely and to do so is DEFINITELY not good for you - or probably people you subsequently come into contact with! In fact it's more a case of anyone who goes to Antarctica needs to come back after not too long. You're quite right about the prison comparison, psychologists have identified that people returning after long stays exhibit similar behaviour to those who have been held prisoner for some time.
Has anyone tried to go down there first and then try to find a job?
Antarctica is not like the rest of the world in this respect. It would be a bit like turning up at an oil or gas rig in mid ocean in a rowing boat and asking for a job - you'd just be asked to leave.
As far as being a videographer is concerned (not sure I know exactly what that means?) film making in Antarctica is not the kind of job that is ever advertised and applied for. It's also not a necessary job for the running of a scientific base.
The vast majority of naturalist film makers are self-employed, especially the ones who go on filming expeditions as opposed to working 9-5 in studios. The skills and personal requirements are just so different that you need to prove yourself first at your own expense usually. I have known such people get their first "break" by taking filming equipment to Antarctica while employed by National Programmes. It has always been a case of buy your own gear, film and pay for processing and then show what the results are. If the results are good enough, you may be able to sell them, after a number of years, you may get a commission from National Geographic, the BBC etc.
The technical quality of the film also needs to be of the highest order meaning that you need the best quality equipment to have any chance of selling the films you make.
You need to be excellent at what you do and the competition is as keen as it possibly could be. Naturalist film making is not a job you apply for, but a job you make for yourself.