For video and stills you want to use two very different shutter speeds. Often when shooting stills, it is best to have the highest shutter speed you can while maintaining the aperture and ISO that you want. Not so for video. If there is any action in your movie, chances are you want to be shooting at a shutter speed of 125 or less. Anything faster and the video will turn out choppy, and not smooth at all. For video the faster the action, the slower the shutter speed. For those of us used to shooting stills, it’s almost counter intuitive.
I often find myself shooting video for a few minutes before remembering this crucial detail, and I can always tell when I am reviewing the footage later, exactly when I switched to the lower shutter speed (compensating aperture and/or ISO to match the new speed.)
One simple option can be to shoot stills in aperture priority and stills in time priority. That way, all you have to do is switch your shooting mode and your camera will then compensate itself accordingly. The other option, if you have presets, is to set one (or more) for your filming settings, while leaving the cameras normal shooting mode set for stills. This way it is a quick twist of a dial (or visit to menu) and you are ready to switch gears. You won’t have to drop your shutter speed way down and then decide how much you need to adjust your ISO and aperture to compensate for the new exposure.