Small fly (~ 2 mm) waving its wings in steady forward rotation on a white mushroom. In common with other web-published videos of Sepsid flies (also called Ensign flies) wing-waving this, one is waving the abdomen. See the clip in the comment below.
Tiny 2-3 mm flies on a 6 cm wide mushroom.
cf. Australosepsis frontalis (On fresh Buffalo dung, Pathumthani Thailand.) www.diptera.info/photogallery.php?photo_id=795