Correct exposure for video capture is complicated by several factors. Even if you’ve mastered it for stills workflows, additional limitations make video capture more difficult. As a photographer, you’re can take advantage of shooting in different program modes for unique situations. Perhaps you enjoy the ease of aperture priority.
When shooting video, you will generally achieve best results by switching all controls over to manual. Your basic tools for exposure control are ISO and aperture. Unfortunately, with video you’ll lose the shutter option as a choice because you’ll want to keep close to 1/50th or 1/60th for natural-looking motion.
To simulate a true filmic image, you need to use the optimum shutter speed to accompany the 24p frame rate in a DSLR.
You can use this simple formula:one second ÷ (frame rate x 2).For example, when shooting 24 fps, you would set your shutter speed to the nearest value, which would generally be 1/50th of a second. At 30 fps, you would use 1/60th of a second.
Following these guidelines will help ensure that the motion blur created by the camera looks natural. You can manipulate shutter speed for a stylized approach, as well as to affect the amount of light hitting the camera’s sensor. However, sticking to a shutter speed of 1/50th or 1/60th of a second is a strongly recommended workflow…
Source: How to Expose a Video Shot