Compressed domain motion vector resampling for downscaling of MPEG video

Digital video databases in compressed form are becoming widely available. In applications such as video browsing, and picture in picture, for a lower bitrate, there is a need to down-sample the video before transmission. The conventional approach to downscale a compressed video sequence is to decompress it at the video server, perform the down-sampling in the pixel domain and then recompress it for efficient delivery. This process is computationally intensive due to the motion estimation process required during the recompression phase. In the alternative compressed domain approach, the motion vectors of the downscaled video sequence are computed directly from the motion vectors of the original full size stream. In this paper we propose a compressed domain technique that generates a better estimate for the downscaled motion vectors. Simulations suggest that the performance achieved with the proposed method is superior by up to 1 dB to the current compressed domain techniques.