The rules of race walking do not allow the athlete to repeatedly have both feet off the ground long enough for it to be perceptible to the unaided human eye. That is a threshold around 50 thousandths of a second of lost contact. The frames in this video are 33 milliseconds apart which means that if there are two consecutive frames showing both feet off the ground during several steps in a row, the athlete is in danger of being given a red card. Three red cards from three different officials would lead to them fouling out and being removed from the competition.
For comparison, a runner is off the ground with both feet for more than 140 milliseconds every step they run.