Benefits of adaptive motion accuracy in H.26L video coding

In video coding standards such as H.263 and MPEG4, the motion vectors are restricted to have the same accuracy for the whole video sequence. In this paper, we explore the benefits of adapting motion vector accuracy at each macroblock of the video frames. We use a Lagrange criterion to select the best motion vectors and their accuracies, and encode them using an adaptive VLC table. We implemented full-search and fast-search versions of our technique in the test model TML-1 of the emerging video coding standard H.26L. In comparison to the original TML-1, which uses fixed 1/3-pixel motion accuracy for all the macroblocks, the proposed adaptive scheme can provide significant coding gains at the cost of slightly increasing computational complexity