Masks or drawings - Complex animations

Halo to my fellow designers! Check out the animation at when you select Fashion style from the menu. Flowers growing and branches multiplying and stuff. I’ve seen this kind of effects in commercials and music videos as well. I’m curious to know what’s the common technique in creating this kind of animation? Is it complex masking or drawing or what? Below are the example pics to give you an idea of what I’m talking about.