We can see smoke at some regions before the main ignition takes place. Why is that?
The white smoke coming from the second stage, and three boosters is LOX venting to relieve the pressure of the LOX turning to gas.
The Liquid Oxygen is sub cooled, so it is even cooler than usual LOX (increases density, more can be stored in tank, and engines produces more thrust) and in the warm Florida sun the tanks start to warm up as soon as the LOX is pumped in.
Normally a booster would just refill the LOX that vents out (And I guess SpaceX does that as well) but because this is sub cooled, just refilling it does not entirely help. This is why SpaceX cannot recycle a launch very fast. Once it warms up too much, they have to pump out all the LOX and refill it.
So you are seeing literally air. Liquid Oxygen, warmed up in the tank to return to gaseous form, and released to relieve pressure in the tanks.