Low bit-rate video transmission for ISDN application

A hybrid coding method for low-bit-rate video transmission over the 2B channels (128 Kb/s) of ISDNs (integrated services digital networks) is presented. In this method the coding frame is divided into two-dimensional m×m blocks where each block is further divided into smaller subblocks (n×n). The transformation is performed on a subblock basis, while block classification and blockmatching motion estimation are based on the larger block size (m×m). The transform coefficients are then encoded in such a way that the intersubblock correlation is efficiently utilized. The coding efficiency can be further improved by the use of adaptive scanning. The quantizer characteristics for the transform coefficients are selected adaptively according to the quantizer masking file, which itself is a function of buffer fullness. The proposed coding method was computer-simulated and its effectiveness evaluated by using two video sequences as the input. The output signals indicate that for videophone application a good-quality video can be obtained at the rate of 112 Kb/s