Dynamic bit-rate reduction based on frame-skipping and requantization for MPEG-1 to MPEG-4 transcoder

In this paper, we propose a dynamic bit-rate reduction scheme for transcoding an MPEG-1 bitstream into an MPEG-4 simple profile bitstream. For dynamic bit-rate reduction, a significant reduction in the bit-rate is achieved by combining the processes of frame-skipping and requantization. For bit-rate reduction by frame-skipping, an efficient method is proposed for estimating the relevant motion vectors from the skipped frames. The conventional FDVS (forward dominant vector selection) method is improved to reflect the effect of the macroblock types in the skipped frames. For bit-rate reduction by requantization, an efficient requantization method is used for an MPEG-1 to MPEG-4 transcoder, consisting of R-Q (rate-quantization) modeling with a simple feedback and an adjustment of the quantization parameters to compensate for the different coding efficiency between MPEG-1 and MPEG-4. Simulation results demonstrated that the proposed method combining frame-skipping and requantization can generate a transcoded MPEG-4 bitstream that is much closer to the desired low bit-rate than the conventional method along with a superior visual quality.