The NTSC format has 29,9 fps and Pal Form. only 25 the pulldown works reducing or ampliating the images.The pulldown works whith a secuence like this swwws (3:2) where W is a complete image and S is an interpolate image based on information of their adjacents(like an deinterlace) ,if you eliminate the pulldown of a 30 fps secuence then the interpolated images was deleted an your secuence is converted automaticaly to an 24 fps secuence.The pulldown causes visual artifacts.Look at combustion help.