How can I adjust brightness when shooting high FPS video? I've FujiFilm Finepix S8500. It is capable of shooting high FPS videos. It works fine in broad daylight but when indoors, the video is always dark. What settings I can adjust to make the video brighter? I tried to adjust ISO and aperture but that does nothing. I also notice that the videos are darker if FPS is higher. I understand why this happens but is there anything to get a brighter video?
Two ways

1) Larger aperture (the lower the number the larger the aperture) letting in more light, but also narrowing your depth of field). 

2)
I would suggest a higher ISO, don't understand why that does not work for you. The current crop of camera's now are absolutely amazing at capturing low light environments that you cannot see with the naked eye.

One of the best cameras for this is the Sony a7s, just released (s for sensitivity).

It needs to be seen to be believed.

                
            

Sony a7s high ISO video link