Constrained trellis based rate control scheme for low bit rate video coding

We propose a new technique of rate control for very low bit rate video coding for visual telephony. The scheme is optimized for a video coder conforming to the H.263 standard and outperforms the linear rate control scheme used in the test model in terms of visual performance and frame jerkiness at the output. The rate control scheme,is designed for a variable bit-rate and variable frame rate coder. We address the rate allocation problem as a constrained optimization problem and exploit the syntax of H.263 to use a constrained trellis to perform the optimization. Furthermore, we reduce the computations in the trellis search by modeling the rate distortion functions. The resulting bit allocation yields a higher signal to noise ratio, and a better correlation between the quantization step size and the block energies, with respect to the linear rate control scheme for the same number of bits assigned for a particular frame