1. A computer implemented method for partitioning a video into a series of semantic units wherein each semantic unit relates to a thematic topic, the method comprising: dividing a video into a plurality of homogeneous segments; analyzing audio and visual content of the video; extracting a plurality of keywords from 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 results of both the audio and visual analysis and the keyword extraction.