Motion-compensated video compression with reduced complexity encoding for remote transmission

Abstract

Abstract Efficient operation at very low bit-rates necessitates a complex encoder that can exploit both spatial and temporal redundancy in a video sequence. To reduce the complexity of such an encoder, we introduce here a new form of motion compensation similar to the conventional hybrid DPCM-transform method but where the compensation is performed outside the feedback loop. In addition to reducing encoder complexity, the proposed out-of-loop (OOL) compensation scheme also supports resolution and frame-rate scalability. While the basic idea is conceptually similar to the pan compensation proposed by Taubman and Zakhor, our method continually tracks and updates the image in the feedback loop in the same way as the conventional DPCM coder. Using OOL compensation, we have observed an average encoder speed increase of 33% on a typical CIF-size video sequence compared to the conventional approach with no significant decrease in decoder speed. Furthermore, we have also found that OOL pan compensation significantly improves the rate-distortion performance of the system relative to conventional pan compensation – taken over five different video sequences, the average bit-rate reduction is 9.2% and the average mean-squared error reduction is 29.6%.