Increased flexibility in inter picture partitioning

Abstract

To attain efficient coding of sequences with complex motion activity, modern video coding standards allow variable block sizes to be employed in temporal prediction. A block with complex motion can be partitioned into two equal-sized halves or into four quadrants. In this paper we study the impact of allowing blocks to be partitioned in two unequal subpartitions. Additionally, we allow block partitioning along diagonal edges. These provisions allows encoders to better adapt to the local characteristics of the motion activity in a video sequence. We verified experimentally that the presence of partitioning edges that do not coincide with transform boundaries does not negatively impact the decorrelating strength of the residual transform, so the proposed extended partitioning strategies can be applied regardless of the details of the residual coder. Implementing the proposed extended partitioning modes in an H.264/AVC coder at the macroblock and submacroblock level, we observe that coding efficiency gains are greatest in low-resolution sequences, where moving features in the video sequence tend to be more spatially localized. For CIF and QCIF sequences we achieve a bit rate reduction of about 3-6% over a wide fidelity range.