The video playback apparatus includes: a video data processor for simultaneously and asynchronously reproducing a main-video stream and a sub-video stream, and controlling position- and size-information of a corresponding display window; and a video output controller, if one of the main- and sub-video streams reproduced by the video data processor is completely reproduced earlier than the other one, which controls the video data processor to enlarge a display window of the remaining video stream to an entire screen size.