According to an embodiment, a display device includes a display, a network interface configured to communicate with an external server, and a controller configured to capture audio content during playback of Audio/Video (A/V) content, acquire a first content identifier based on the captured audio content, display a first pop-up window corresponding to the acquired first content identifier on the display, when a mute interval is continued for a predetermined time, capture video content, acquire a second content identifier based on captured video content, and, when the acquired second content identifier is not identical to the first content identifier, display a second pop-up window corresponding to the second content identifier on the display.