Rate distortion optimized slicing over bit error channels

In this paper, we study the problem of optimizing slice sizes and locations for video transmission over bit error channels. We propose a method that utilizes estimation of slice rate and distortion which is a function of the inter-macroblock dependency as exploited in the video codec. First we experimentally show that our estimation is effective. Since there are practically numerous possibilities for slice configurations and one must actually check all possibilities for a complete search, we assume segmentation of macroblocks so that a slice can only start at the segments. Although this results in a slightly suboptimal solution, it reduces the number of possibilities. However there are still practically too many configurations. Then we use the proposed RD estimation method and combine it with a dynamic programming approach to effectively determine the most optimal slice configuration. RD optimization is carried out in terms of minimizing the expected Lagrangian using the expected distortion of a slice. We assume that the physical layer is capable of generating an error report showing which transmission units are received in error. This allows us to use NEWPRED with macroblock level feedback and prevent wrongful decoding of erroneous macroblocks. We compare the proposed system with the two common approaches namely, fixed number of MBs per slice and fixed number of bits per slice and see that the proposed method performs better than both. © 2005 SPIE and IS&T