It is now thought that all of the theropods had feathers. This video tanks an interesting view on how dinosaurs evolved into birds with the focus on explaining how a useless, basically half wing possessed by theropods, evolved into a full will capable of flight.
The two prevailing theories are: One, dinosaurs climbed trees and glided down eventually developing flight. Two, dinosaurs ran faster and faster and used their feathered arms for leverage and speed and eventually developed flight. This video explores a third, and relatively new option for how flight might have developed.