<title>Efficient implementation of a video transcoder</title>

Abstract

Given a video stream encoded with a particular bit rate and compression scheme (C<SUB>1</SUB>), transcoding the video stream refers to the process of re-encoding the input compressed stream at a different bit rate and possibly with different spatial resolution, temporal resolution and compression scheme (C<SUB>2</SUB>). In this paper the special case of a transcoder which has a 4:2:2 format video stream as it's input and produces a 4:2:0 output stream at a lower bit rate is considered. Further more, it is assumed that both C<SUB>1</SUB> and C<SUB>2</SUB>, like nearly all standard video compression algorithms, use 8 x 8 block DCT based compression. In this context, it will be shown how standard implementations of transcoders, as proposed by Ghanbari and others may be simplified to obtain a reduction in the transcoder implementation complexity. In particular the problem of simplifying the process of down conversion from 4:2:2 to 4:2:0, so that this process can take place directly in the DCT domain, will be addressed. The MPEG-2 video standard treats interlaced and progressive video differently for compression purposes; the proposed scheme is shown to be applicable to both cases. Simulation results show that this simplification does not result in performance degradation when compared with standard, high complexity implementations.