Provided are an artificial intelligence (AI) system that mimics cognitive functions, such as cognition and judgment, of the human brain using a machine learning algorithm such as deep learning and applications thereof. More particularly, provided is a device including a memory storing least one program and a first video, a display, and at least one processor configured to display the first video on at least one portion of the display by executing the at least one program, wherein the at least one program includes instructions for: comparing an aspect ratio of the first video with an aspect ratio of an area in which the first video is to be displayed, generating a second video corresponding to the aspect ratio of the area by using the first video when the aspect ratio of the first video is different from the aspect ratio of the area, and displaying the second video in the area, wherein the generating of the second video is performed by inputting at least one frame of the first video to an AI neural network.