1. A video processing method, comprising: acquiring a plurality of video streams each including moving picture data item and sound data item; extracting one or more feature values indicating a common feature between the video streams and changing in time series, by analyzing at least one of the moving picture data item and the sound data item for each video stream; generating a plurality of segments by dividing each of the video streams in accordance with changes in the one or more feature values, and generating associated segment groups by comparing the first feature values for each of the segments to obtain similarities and associating a plurality of segments in different video streams such that the segments included in each of the associated segment groups have a similarity not less than a first threshold value; extracting, from the associated segment groups, one or more common video segments in which the number of segments included therein is not less than a second threshold value; calculating a first summarization score indicating a degree of suitability for including the one or more common video segments in a summary video, the first summarization score being defined for each common video segment and varying with time and being based on the one or more feature values; selecting a common summarization segment to be used for the summary video from the common video segments based on the first summarization score; extracting, from the associated segment groups, one or more individual video segments in which the number of segments included therein is not more than a third threshold value that is less than the second threshold value; calculating a second summarization score indicating a degree of suitability for including the one or more individual video segments in the summary video, the second summarization score being defined for each individual video segment and varying with time and being based on the one or more feature values; selecting an individual summarization segment to be used for the summary video from the individual video segments based on the second summarization score; and integrating the common summarization segment and the individual summarization segment to create the summary video.