  Motion compensated prediction is central to the efficiency of video
compression. Its predictive coding scheme propagates the quantization
distortion through the prediction chain and creates a temporal dependency.
Prior research typically models the distortion propagation based on the
similarity between original pixels under the assumption of high resolution
quantization. Its efficacy in the low to medium bit-rate range, where the
quantization step size is largely comparable to the magnitude of the residual
signals, is questionable. This work proposes a quantitative approach to
estimating the temporal dependency. It evaluates the rate and distortion for
each coding block using the original and the reconstructed motion compensation
reference blocks, respectively. Their difference effectively measures how the
quantization error in the reference block impacts the coding efficiency of the
current block. A recursive update process is formulated to track such
dependency through a group of pictures. The proposed scheme quantifies the
temporal dependency more accurately across a wide range of operating bit-rates,
which translates into considerable coding performance gains over the existing
contenders as demonstrated in the experiments.
