The University of British Columbia

This paper introduces a new H.263-based video coding algorithm for operation at very low bit-rates. Although the algorithm is also based on block-based motion estimation/compensation and DCT coding, it is very different from conventional H.263 algorithms. Our algorithm employs (1) a rate-distortion-based mechanism to select amongst the H.263 macroblock coding types, (2) a fast median-based predictive motion searching technique, (3) a Lagrangian minimization for estimating the motion vectors, and (4) semi-fixed-length coders for coding the motion vectors and the DCT coefficients of the 8x8 motion-compensated prediction difference blocks. Experimental results indicate that the proposed algorithm significantly outperforms Telenor's H.263 video coder both in terms of compression performance and computational complexity, while still producing a more error resilient bit stream. Another important advantage of our algorithm is that the bit-rate, quality, and number of computations can be controlled through manipulating the Lagrangian and threshold parameters. This feature is usually desired in many very low bit-rate video communication applications due to power and mobility constraints. (C) 1997 Elsevier Science B.V.