Pentax K-5 and shutter speed while recording a movie

Hello,

I would like to know what there is shutter speed while recording a movie. As fas as I remember I can set an apperture, ISO, but I cannot the shutter speed. Recording Full HD 25 FPS I should set 1/50s but in K-5 it is rather impossible. Does anybody know how K-5deals with it? How oes it set the shutter speed?

Thank you in advance.

Alek