Macroblock quantizer selection for H.263 video coding

We consider two MSE-based strategies for selecting the best quantization parameter (Q) for each coded macroblock in H.263 video coding. In the first study, Q was adjusted to match a target mean-squared error (MSE) for each block. The goal was to avoid having large errors in a few macroblocks that detract from the overall perceived image quality. Effectively, we minimized peak MSE over all macroblocks. In a second study, we sought to minimize the average MSE, modifying a gradient-search technique that has been applied to H.261 [1]. The choice of quantizers was limited by H.263 syntactical constraints on changes in Q between successively-coded macroblocks. The results were compared with fixed Q encoding. The resulting sequences displayed only small perceptual differences, For the cases studied, the primary advantage of varying Q was to control delay.