Field - to - Frame Transcodingwith Spatial and Temporal

FIELD-TO-FRAME TRANSCODING WITH SPATIAL AND TEMPORAL DOWNSAMPLING Susie J. Wee, John G. Apostolopoulos Hewlett-Pa kard Laboratories Palo Alto, CA USA Ni k Feamster Massa husetts Institute of Te hnology Cambridge, MA USA ABSTRACT We present an algorithm for trans oding high-rate ompressed bitstreams ontaining eldoded interla ed video to lower-rate ompressed bitstreams ontaining frameoded progressive video. We fo us on MPEG-2 to H.263 trans oding, however these results an be extended to other lowerrate video ompression standards in luding MPEG-4 simple pro le and MPEG-1. A onventional approa h to the trans oding problem involves de oding the input bitstream, spatially and temporally downsampling the de oded frames, and re-en oding the result. The proposed trans oder a hieves improved performan e by exploiting the details of the MPEG2 and H.263 ompression standards when performing interla ed to progressive (or eld to frame) onversion with spatial downsampling and frame-rate redu tion. The trans oder redu es the MPEG-2 de oding requirements by temporally downsampling the data at the bitstream level and redu es the H.263 en oding requirements by largely bypassing H.263 motion estimation by reusing the motion ve tors and oding modes given in the input bitstream. In software implementations, the proposed approa h a hieved a 5x speedup over the onventional approa h with only a 0.3 and 0.5 dB loss in PSNR for the Carousel and Bus sequen es.