Relying on a rate constraint to reduce Motion Estimation complexity

TL;DR

This paper introduces a rate-based candidate elimination method for Motion Estimation that significantly reduces encoder complexity by limiting search candidates based on motion vector bitrate, with minimal impact on compression efficiency.

Contribution

It presents a novel, flexible rate constraint approach for Motion Estimation that can be integrated into various search strategies to reduce computational complexity.

Findings

Over 80% reduction in Motion Estimation complexity

Average 0.74% increase in BD-Rate

Applicable to multiple ME strategies

Abstract

This paper proposes a rate-based candidate elimination strategy for Motion Estimation, which is considered one of the main sources of encoder complexity. We build from findings of previous works that show that selected motion vectors are generally near the predictor to propose a solution that uses the motion vector bitrate to constrain the candidate search to a subset of the original search window, resulting in less distortion computations. The proposed method is not tied to a particular search pattern, which makes it applicable to several ME strategies. The technique was tested in the VVC reference software implementation and showed complexity reductions of over 80% at the cost of an average 0.74% increase in BD-Rate with respect to the original TZ Search algorithm in the LDP configuration.