The more active bird in the video linked is a good example of how to tell a cock from a hen.
It is a pretty good rule of thumb that if a pigeon "bows and scrapes" or displays other courtship behaviors while pursuing a second bird, it is probably a cock.
By contrast, there is no hard and fast rule to identify a hen, as hens have no particular behavior patterns to identify them by. (And quite often an unmated hen will respond to a pursuing cock with behavior somewhat similar to his. In the video, I actually suspect that the second bird is not sexually mature as it does not respond to the cock, though it does LOOK like a young hen. Most unmated mature hens would respond to a courting cock, while most mated hens will attempt to fight a little with a cock other than their mate that is pursuing them).
Mostly, determining the hens is a process of elimination of the birds that are not cocks. It is all about observation. Don't let anyone ever tell you that every clutch of eggs is always a "pair (ie. a cock and a hen) or that they can look at a pen of twenty 5 week old squeakers and pick out which ones are cocks and which are hens. Some long time fanciers are pretty good at sexing mature birds on sight, at least in some breeds, at least.
Unlike chickens, in pigeons and doves, the male and female look alike (hens often are smaller though, and may have more graceful looking heads and beaks).
That said, there are no hard and fast rules to sexing pigeons unless you use sex-linked matings. Some hens can act pretty bully, while some cocks act more like hens.
Even after over 35 years at this, I still get a few that fool me for awhile. As one example, I have a little Red Check Self cock that for well over a year I was convinced was a hen, even after he set up house keeping with a Dark Check Self that I knew for fact was a hen, as the clutch of eggs she laid turned out to be infertile. I was pretty sure it was two hens mated up, which they often will do if no cocks are present. It wasn't until the next round was actually fertile that I realized the Red Check was a cock. It was only after yet another clutch of eggs that the Red Check started displaying the behavior of a cock.