What types of information in key-frames of a storyboard are critical when users extract the meaning of a video? For this research question, we reviewed the literature and then conducted the preliminary study. Next, based on the literature review and our findings from the preliminary study, we constructed the two-step model for video key-frame determination. We set the hypothesis that the proposed two-step method will produce more meaningful key-frames than the mechanical method (by which key-frames are extracted simply at an interval of few seconds or minutes) in terms of summarizing a video. In order to testify the hypothesis, we conducted an experiment to compare the storyboards constructed based on the proposed two-step method to those built based on the mechanical method. The two-step model showed better accuracy in identifying the content of a video.