<title>Reference-frame representation in the transform domain for H.261 video compression</title>

Abstract

To deal with the temporal redundancy of an input video sequence H.261 Standard specifics to use displaced frame differences with reference frames and, optionally, motion compensation technique. Usually, encoding process is performed in a loop comprising reconstruction of a reference frame in spatial domain along with the computation of a difference between a successive input video frame and its reference, followed by DCT compression of that displaced frame difference. In this paper we show that the reference frames can be reconstructed in the transform domain instead, having no impact on the computational accuracy and output bitstream. In this way, we represent all reference frames in the transform domain in a form of dequantized DCT coefficients, so the next inter-frame is a difference between the next DCT-transformed input picture and the current reference frame. This inter-frame is then quantized and entropy encoded on a regular basis. The output bitstream remains to be H.261-compliant, while the compression ratio as well as quality of the decompressed video are the same as in conventional implementation. We also present the performance results for the software codec running on Pentium PC.