System and method for partitioning a video into a series of semantic units where each semantic unit relates to a generally complete thematic topic. A computer implemented method for partitioning a video into a series of semantic units wherein each semantic unit relates to a theme or a topic, comprises dividing a video into a plurality of homogeneous segments, analyzing audio and visual content of the video, extracting a plurality of keywords from the speech content of each of the plurality of homogeneous segments of the video, and detecting and merging a plurality of groups of semantically related and temporally adjacent homogeneous segments into a series of semantic units in accordance with the results of both the audio and visual analysis and the keyword extraction. The present invention can be applied to generate important table-of-contents as well as index tables for videos to facilitate efficient video topic searching and browsing.