Drift Compensated Coding Optimization for Fast Bit-rate 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, open-loop 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 drift-compensated coding optimization scheme, by which generated bitstreams can be effectively transcoded into lower bitrate by open-loop transcoder with little drift propagation. The encoder integrates a virtual open-loop 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.264/AVC.