Where do the famous "black bars" come from?!

Hi all,

Still new and learning, can i ask, at what point in a dvd rip do the "black bars" at bottom and top of the file appear? Does is depend on the original DVD? I use DVDfab to rip and then Handbrake to encode, is this something i can adjust? If i already have an encoded file with it can i change this?

Sorry for all the questions, im finding a step learning curve!

Thanks for any advice.