EFFICIENT H.261-BASED 2-LAYER VIDEO CODECS FOR ATM NETWORKS

Two methods for bit-rate reduction of two-layer video codecs, without impairing their robustness to cell loss are introduced, Both methods employ an H.261 compatible coder at the base layer and an interframe coder at the second layer. In the first method a second H.261 is used to code the residual errors of input pixels, Parameters of this Twin-H.261 codec in terms of effect of motion estimation, resilience to cell loss and forced updating are investigated, The second method employs an interframe coder among the enhancement DCT coefficients (Inter-Enhance) of successive frames of similar frequencies. Introduction of a leaky prediction in the interframe loop preserves the coder resilience to cell loss. Optimum value of the leak factor is found to be in the range of 0.85-0.95. It is shown that while both Twin-H.261 and Inter-Enhance codecs generate bit rates close to the one-layer coder, their resilience to cell loss closely follows the normal two-layer coder.