A device comprising: a memory storing at 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 comprises 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, wherein the area is an entire area of the display; when the aspect ratio of the first video is different from the aspect ratio of the area, generating a second video corresponding to the aspect ratio of the area, the second video including a video expansion part and at least one portion of the first video, and displaying the second video in the area, wherein the generating of the second video comprises: identifying a letterbox to be displayed in the area when the aspect ratio of the first video is different from the aspect ratio of the area; generating the second video including the video expansion part, the video expansion part to be displayed in the letterbox, by generating a frame of the second video corresponding to a reference frame by inputting, to an artificial intelligence, Al, neural network, the reference frame being included in the first video, at least one previous frame, and at least one next frame, or by inputting, to the AI neural network, the reference frame being included in the first video and a resized frame obtained by resizing the reference frame, and wherein displaying the second video in the area comprises displaying the video expansion part in the letterbox. a memory storing at 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 comprises 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, wherein the area is an entire area of the display; when the aspect ratio of the first video is different from the aspect ratio of the area, generating a second video corresponding to the aspect ratio of the area, the second video including a video expansion part and at least one portion of the first video, and displaying the second video in the area, wherein the generating of the second video comprises: identifying a letterbox to be displayed in the area when the aspect ratio of the first video is different from the aspect ratio of the area; generating the second video including the video expansion part, the video expansion part to be displayed in the letterbox, by generating a frame of the second video corresponding to a reference frame by inputting, to an artificial intelligence, Al, neural network, the reference frame being included in the first video, at least one previous frame, and at least one next frame, or by inputting, to the AI neural network, the reference frame being included in the first video and a resized frame obtained by resizing the reference frame, and wherein displaying the second video in the area comprises displaying the video expansion part in the letterbox. comparing an aspect ratio of the first video with an aspect ratio of an area in which the first video is to be displayed, wherein the area is an entire area of the display; when the aspect ratio of the first video is different from the aspect ratio of the area, generating a second video corresponding to the aspect ratio of the area, the second video including a video expansion part and at least one portion of the first video, and displaying the second video in the area, wherein the generating of the second video comprises: identifying a letterbox to be displayed in the area when the aspect ratio of the first video is different from the aspect ratio of the area; generating the second video including the video expansion part, the video expansion part to be displayed in the letterbox, by generating a frame of the second video corresponding to a reference frame by inputting, to an artificial intelligence, Al, neural network, the reference frame being included in the first video, at least one previous frame, and at least one next frame, or by inputting, to the AI neural network, the reference frame being included in the first video and a resized frame obtained by resizing the reference frame, and wherein displaying the second video in the area comprises displaying the video expansion part in the letterbox. identifying a letterbox to be displayed in the area when the aspect ratio of the first video is different from the aspect ratio of the area; generating the second video including the video expansion part, the video expansion part to be displayed in the letterbox, by generating a frame of the second video corresponding to a reference frame by inputting, to an artificial intelligence, Al, neural network, the reference frame being included in the first video, at least one previous frame, and at least one next frame, or by inputting, to the AI neural network, the reference frame being included in the first video and a resized frame obtained by resizing the reference frame, and wherein displaying the second video in the area comprises displaying the video expansion part in the letterbox.