Conditional Motion Vector Refinement for Improved Prediction

Adapting the resolution of motion compensated prediction in a video codec is considered in this paper. A new motion search and signaling scheme for increasing the accuracy of prediction without affecting the complexity of encoding is proposed. It involves using common information available to both encoder and decoder, e. g. current slice type, texture in reference pictures, etc as a cue to control motion vector accuracy and an efficient reuse of motion information for predicting subsequent blocks. An average bit rate reduction of around 2.5% for P-pictures and 0.5% for B-pictures is observed with no extra search compared to a fixed quarter-sample resolution.