High resolution video has now surpassed the detail necessary for professional-sized prints. Techniques that make it easier to pull stills from video are therefore becoming increasingly important.
At 1080P, the largest print one could create was about 4×6 inches at 300 PPI. That was sometimes useful, but usually meant separate DSLR photography was needed for printed advertisements. The advent of 4K+ resolution has been a game-changer though; for the first time, more than enough detail gets captured for two-page magazine spreads or even billboards.
However, resolution isn’t the only enabler. Having a virtually continuous stream of stills from a subject makes results more predictable and consistent — because botched timing, framing and focus become less likely. One now has the ability to select just the right placement or expression; blinking during portraits, unintentional motion blur, and missed moments are all potentially things of the past.
Perhaps the biggest distinction is that while some motion blur is often desirable with video—to render smoother camera and subject movement—this is often undesirable with still images. One way to overcome this problem is to use a smaller shutter angle. For example, with 24 fps cinema the standard shutter angle is 180 degrees, which translates into a shutter speed of about 1/50 of a second. However, many stills scenarios, including sporting events and hand-held telephoto shots, typically need 1/250 of a second or faster.
If subject blur is primarily due to camera shake instead of subject motion, one can use video as a form of image stabilization – by picking the frames with the least camera shake. This technique is especially helpful with hand-held telephoto shots, since these amplify the appearance of most camera movements. Video also makes it easier to hold a camera steady, since one no longer has to simultaneously press a shutter button, or anticipate holding still for a specific moment.
Misfocus and improper exposure can also cause still photographs to become unusable. As insurance, one can effectively bracket their stills by varying the lens aperture during the shoot, or by slowly rocking the focus with a razor-thin depth of field.
See full details and examples of Shooting Motion for Stills on the RED 101 Article: SHOOTING VIDEO FOR STILLS