An algorithm is proposed for block-motion estimation and coding characterized by fast computation and very low bitrate. For each block, a spatio-temporal context is defined based on nearest neighbors in the current and previous frames, and a prediction list is built. Then, the best matching vector within the list is chosen as an estimation of the block motion. Since coder and decoder are synchronous, only the index of the selected vector is needed at the decoder to reconstruct the motion field. Furthermore, bitrate saving is achieved through a context-based sorting of the prediction list of each block, which allows to reduce the entropy of the motion indexes. To avoid the propagation of the error, an additional correction vector can be sent when prediction error exceeds a threshold.

Tests demonstrate that the proposed method ensures a speed up over 200 as compared to classical full search, achieving at the same time a coding gain above 2, with a negligible loss of accuracy. This allows real-time implementation of VLBR software video coders on conventional PC platforms.