Motion trajectory extraction based on macroblock motion vectors for video indexing

As video sequences are composed of dynamic video objects (VOs) in nature, VO´s motion is an effective feature used to provide an overall description about the content of video sequences. In this paper, we propose a novel video indexing technique that extracts VO´s motion trajectory based on macroblock motion vectors (M-Vs) of MPEG encoded bitstreams, without performing full decoding. This is an attractive approach, as it promises large saving of computation and memory storage. The proposed motion trajectory extraction algorithm comprises two phases: (i) unsupervised VO segmentation and (ii) automatic tracking of each segmented VO. Experimental results reveal promising potential of the established algorithm in extracting VOs´ motion trajectories from the limited information provided by MVs