Multiple Global Affine Motion Model for H.264 Video Coding with Low Bit Rate

摘要

A multiple global affine motion model is proposed for low bit rate video compression. Block-wise motion segmentation is first performed with the number of motion objects L predefined. The affine motion models for multiple MOs are estimated and coded in the frame header. The scaling parameters a1, a2, a4 and a5 are coded with a 4-dimensional vector-quantizer (VQ), whose 16 most recently used code words are maintained on line and searched for VQ match, and the 300-word long main code book stored offline. The translational parameters a3 and a6 are coded predicatively as a classical motion vector. L new macro-block modes are added to the standard's list of 7 intra and inter modes. No segmentation information is transmitted, for the mode already indicates that if one of the affine modes is selected by Lagrange rate-distortion optimization. A metric S is defined to measure locality of the motion and will disable use of affine models when a threshold is surpassed. Simulation shows that abut 20-40% of the MB's choose one of the affine modes. When l00kbps or lower bandwidths are available, the proposed codec not only saves 1～18% bit rate, but also enhances error-resilience in multiple slice frames and reduces blocking artifacts notably.