I`ve made some tests.
Seems WiFi physical interface guarantees delivery of the package for unicast IP, even it is UDP packet on protocol layer.
I have 26 RTP-AP frame, which have about 15-17 separates packets. There is no packets lost, so video is fine, too.
But, when I try to send for broadcast, I have loss rate about 3-12% depended on distance, etc , and if only 1 packet in a frame is lost - all frame lost too for decoder on receiver side. That`s why video have lags. Even with good quality WiFi 3%*15=45% packets lost.