Stills vs Videos. Time is the fourth dimension a 4d ultrasound can gather 3d volumes and show motion and movement over time. This represents the difference between video and a still.
Fun pictures. 3d and 4d ultrasounds are images obtained with special probes and machines that can give pictures of the fetus in three dimension. This can give beautiful pictures of the facial features, the limbs, body etc. A still picture is 3d and watching the screen and the baby moving is the 3d image. Enjoy the experience, fun to see baby move.