I realize this question is from October, but I have recently discovered a cross-over mallard (hen-to-drake) on my pond, so thought I'd give my thoughts.
The one in your video I believe is drake, based on his beak color. For some reason his color molt may be less progressed than your others.
The one on my pond has orange beak but her colors feathers have chnaged into rough-out drake colors. (Some green on the head, a white neck band, gray flight feathers, dark breast). Still spotty and not a perfect change. My research found that hens can do this change if their ovary has been damaged. The feather colors will change but not the beak. A drake can not change to a hen, so if the beak is greenish-yellow it is a drake.
