Efficient Intra Mode Selection Using Motion Affected Region Tracking Intra refresh is wellknown as an efficient technique for eliminating temporal error propagation in a predictive video coding system. This paper proposes a novel intra refresh method based on motion affected region tracking (MTIR) for real time video communication systems. For every frame between two successive intra refresh frames, the motion affected regions are statistically analyzed to achieve the error sensibility of macroblocks, and then the error sensitive macroblocks are intra coded. To suppress the potential spatial and temporal error propagation, constrained intra prediction with limited DC prediction (LDC) is used for the refreshed macroblocks, which has also been adopted by the mobile profile of Chinese audio video standard (AVS) in Mar. 2009. In addition, the reference of inter predicted frame which behinds an intra refreshed frame is limited. Experimental results on JM15.1 show that compared with traditional methods, the proposed method can achieve a considerable gain on objective peak signal noise ratio (PSNR) about 0.5 to 1.5 dB, and the subjective visual quality of reconstructed videos can also be obviously improved.

Drift compensated coding optimization for fast bitrate reduction transcoding Bit rate adaptation is one of the basic problems in universal multimedia access. Therefore, in many cases, there exists a strong requirement for a very fast transcoding implementation. Usually, openloop transcoding architecture is the desired solution with the lowest computational complexity. However, severe drift error makes it infeasible to most applications. In this paper, we propose a driftcompensated coding optimization scheme, by which generated bitstreams can be effectively transcoded into lower bitrate by openloop transcoder with little drift propagation. The encoder integrates a virtual openloop transcoder, in which drift error is effectively compensated by suitably adjusting the RD based mode selection and motion estimation for each macroblock. Simulation results show that compared with traditional coding, the proposed mode selection scheme can yield better coding efficiency when rate reduction transcoding to low bitrate occurs. And meanwhile, it does not degrade the coding efficiency in comparison with the normal single layer coding in H.264AVC.