Intra/inter macroblock mode decision for error-resilient transcoding

When transmitting the precoded bitstream over an error-prone network, error-resilient transcoding is adopted to convert the bitstream to a resilient format for robust delivery. Intra refreshment is an efficient tool to reduce the dependency between frames and stop the channel error propagation. In the conventional scheme, the rate-distortion optimized macroblock mode decision is employed to adaptively determine the coding mode of each macroblock. However, this scheme only considers the channel error propagated from the previous frames to the current frame. As opposed to this traditional algorithm, this paper proposes a method which considers consecutive two frames in a sequence, thus taking the error propagation to the following frame into account. This enhances the overall robustness of the transcoded bitstream against the packet loss. Considering the availability of the next frame information, two cases are discussed respectively. Experimental results show that the proposed methods present quality improvement when compared with the conventional rate-distortion optimized error-resilient coding scheme under different test environments, and the PSNR improvement can reach as high as 0.9 dB.