| The emerging H.264 video coding standard provides state-of-the-art video coding techniques and has significant coding performance improvement over existing standards. The general objective of this research is to reduce the H.264 encoder complexity without significant RD performance degradation. In particular, we have focused on the complexity reduction for the coding mode decision and motion estimation, which are the modules that demand a high computational cost in the encoder.; For the improved coding mode decision, we develop an efficient two-stage framework. Fist, a coarse level intra/inter coding mode prediction is performed to decide the class. The proposed algorithm calculates three features and maps them into the one of three regions; namely, risk-free, risk-tolerable, and risk-intolerable regions. Depending on the mapped region, we can apply algorithms of different complexities for the final mode decision. Based on the coding mode decision result, either intra predictive coding or inter predictive coding process is proceeded in macroblock adaptive manner. In case of intra predictive coding, we propose a fast intra mode decision scheme for the fine-level mode decision.; For inter predictive coding, a fast multiple reference assignment scheme for efficient motion estimation is proposed. First, the dynamic block-size effect on time-varying sequence characteristics is quantified by its impact on the RD performance degradation. The block-size effect on the RD coding gain is exploited to develop a new algorithm, called the block-size adaptive referencing (BAR) scheme, that assigns a different number of references in a block-size adaptive manner. The proper BAR scheme can be chosen to minimize the reference frame numbers while keeping the expected RD loss under a target level. Finally, fast motion search is performed within selected references in a block-size adaptive manner and the model parameters are adjusted using the normalized LMS adaptive filter to accommodate time varying sequence characteristics. The proposed algorithms can save considerable computational complexity of H.264 reference code with negligible degradation in the RD performance. |
