This document describes a prototype video compression system based on motion-compensated wavelet coding. The system incorporates tools for motion estimation and motion compensation based on overlapped blocks to eliminate block artefacts. Entropy coding is based on adaptive arithmetic coding, and the coder is capable of trading off the bit rate of different elements of the bitstream using Rate-Distortion Optimisation techniques. The codec has not been very extensively tested or optimised, but the performance to date suggests that improvements of the order of 2-3dB over MPEG-2 can be achieved, together with an absence on blockiness at low bit rates. Together this results in an approximate halving of bitrate for the same perceived quality.
This document refers to Version 0.4.0 of Dirac.
Written by Thomas Davies, BBC R&D. Last revised 17 August 2004