Two-layer coding for videotelephone

Abstract

Design of a two-layer coding scheme is considered under the constraint that the first layer running at 64 kbit/s is to perform the normal H.261 functions. The second layer is recruited optionally to enhanced the image quality and/or to increase the frame rate. In the chosen scheme, the second laeyr processes the difference between the original signal and the reconstruction of the first layer, by a combination of DCT and pixel correction techniques. While SNR improvements achieved were of the order of 1 dB, subjective tests indicated a much stronger preference for the two-layer codec.