Brake pedal is soft

So for a while now when i press the brake pedal the first inch or so of the pedal is very soft, the rest being hard. The car brakes normally i just have to press the pedal harder. It didn't used to be like that, i would just barely touch the pedal and the car would brake.

Today i asked my brother to press the brake pedal with the engine turned off and the hood opened and i could hear air being blew out in the engine bay when he pressed the pedal.

What do you guys advise me to do? What is the problem?

Thanks

Brake pedal is soft