Boom is really a misleading word for it because it implies something like an explosion – when really it’s more of a constant roar. It just sounds like a boom from land, because unlike normal sound, which would reach you from the plane constantly as it flies by, the boom is like the wake of a boat, only hitting you once for each pass.
I think part of the reason this isn’t well known is because of all the photos of jets breaking the sound barrier.
That plane wasn’t going supersonic though. The cone happens at transonic speeds, so when the plane is accelerating, as it nears Mach 1 a shock cone can appear. You can tell in the video that it is very close to Mach 1 because there is no sonic boom and the sound from the plane appears just before it passes.