A novel DCT domain transcoder for transcoding video streams with half-pixel motion vectors

Video transcoding is one of the key techniques to provide heterogeneous multimedia applications with Universal Multimedia Access (UMA) service. Recently, compressed domain (DCT, Discrete Cosine Transform) transcoding architectures have been proposed to achieve fast transcoding, in which DCT domain Inverse Motion Compensation (IMC) is the most important module to reduce computational complexity. The problem of IMC has been studied for integer-pixel precision motion vectors (MVs), and, subsequently, for half-pixel precision MVs in which extra filtering, hence, extra computation is introduced. Since most current video coding standards, such as H.263, MPEG-2, etc., use half-pixel precision MVs to achieve better quality, reducing computational complexity of IMC for half-pixel MVs is important for real time fast transcoding video streams encoded by these standards. In this paper, we propose a novel half-pixel filter for IMC, which simplifies the extract operations by integrating the interpolation and translation operations into one single step. Compared to other existing half-pixel filtering algorithms, the proposed filter does not introduce any distortion and drift errors. Experimental results demonstrate that the proposed filter achieves faster transcoding than other DCT domain transcoders, and almost the same video quality as that of pixel domain transcoders. (C) 2004 Elsevier Ltd. All rights reserved.