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.

Hybrid Bitstream Rewriting from Scalable Video Coding to H.264AVC Scalable Video Coding (SVC) is an extension of H.264AVC standard. The base layer of SVC is compatible with H.264AVC standard, while the enhancement layers provide desired temporal, quality andor spatial scalabilities. Bitstream rewriting in SVC standard allows an SVC bitstream to be converted to an H.264AVC bitstream without quality loss and preferably with low computational complexity. However, current rewriting is only supported in quality scalability rather than spatial scalability, which limits the application in many practical scenarios. In this paper, a hybrid bitstream rewriting approach to support both quality and spatial scalability is proposed based on the principle of residue upsampling in transform domain. The computational complexity of the proposed approach is much lower than the conventional scheme of cascading transcoding. Extensive experimental results demonstrate that the loss of the ratedistortion (RD) performance of the proposed rewritable SVC bitstream is acceptable compared with the conventional SVC bitstream, however, the RD performance is better than that of simulcast. Furthermore, the RD performance of the H.264AVC bitstream rewritten from the rewritable SVC bitstream is even better than that of the input SVC bitstream. Compared with the cascading transcoding scheme, the proposed hybrid rewriting can achieve 0.8 dB YPSNR gains while saving 80% processing time on average.