An Improvement to Merge Mode in ECM With Template Matching

In the development of video coding standard, decoder-side motion derivation technology has been proven to provide promising coding efficiency. With this type of technology, the motion information is derived at the decoder instead of being signaled in the bitstream by the encoder, and thus, the number of bits to be sent are reduced. A typical decoder-side derivation technology is template matching, which refines the motion by finding the closest match between neighboring reconstructed samples and corresponding reference samples in the reference pictures. In this paper, the template matching method is extended to temporal motion vector predictor, bi-prediction with CU-level weight and geometric partition modes in order to fully utilize its benefit. Specifically, template matching is used to determine the prediction direction and reference picture of temporal motion vector predictors, and to decide the bi-predicted weight of bi-prediction merge blocks. In addition, the motion of two geometric partitions are individually refined by the template matching mechanism. Simulation results show that on top of Enhanced Compression Model (ECM), which is the software platform for exploring activities beyond versatile video coding established by the joint video experts team (JVET), the three proposed methods achieve 0.20% luma BD-rate savings in random access configuration and 0.33% luma BD-rate saving in low delay B configuration with negligible encoding and decoding runtime impact. It is worth noting that all three proposed methods have been adopted to the ECM software platform.