On Using Raw MPEG Motion Vectors To Determine Global Camera Motion

This document reports a simple and effective method to determine global camera motion using raw MPEG-1 motion vectors information obtained straight from the real MPEG-1 streams such as that of the new HITACHI MP-EG1A digital camcorder. The simple approach we have experimented with robustly fits a global affine optic flow model to the motion vectors. Other more robust methods are also proposed. In order to cope with the Group-ofFrames (GOF) discontinuity of the MPEG stream, B frames are used backward to determine the “missing link” to a previous GOF thereby ensuring continuity of the motion estimation across a reasonable number of frames. As a testbed, I have applied the method to the image mosaicing problem, for which the interesting results obtained are presented. Although several other methods exists to perform camera motion estimation, the approach presented here is particularly interesting because exploits “free” information present in MPEG streams and bypass the highly expensive correlation process.