An efficient motion vector composition algorithm for fast-forward playback in a video streaming system

Fast-forward playback enables viewers to scan through the video scene of interest efficiently. One approach to realize fast-forward playback is to employ a frame-skipping transcoder which transcodes only the frames required for playback at the desired fast speed. Various motion vector composition algorithms are used to compose the new motion vectors with reduced complexity. These algorithms do not work well for dropping a large number of frames, which is very common in fast-forward playback. In this paper, a new multiple-candidate vector selection algorithm (MCVS) is proposed to select a composed motion vector from a set of candidate motion vectors, which utilizes relevant areas in the target macroblock to ensure a reliable tracking process for motion vector composition. Experimental results show that the proposed MCVS can provide fast-forward playback through video transcoding with significant gain, in terms of rate-distortion performance, especially when a large speed-up factor is required.