Can motion vectors be used to determine object velocity?
Motion vector information cannot be reliably used as a means of determining object velocity unless the encoder model specifically set out to do so. First, encoder models that optimize picture quality generate vectors that typically minimize prediction error and, consequently, the vectors often do not represent true object translation from picture-to-picture. Standards converters that resample one frame rate to another (as in NTSC to PAL) use different methods (motion vector field estimation, edge detection, et al) that are not concerned with Rate-Distortion theory. Second, motion vectors are not transmitted for all macroblocks anyway. Is it possible to code interlaced video with MPEG-1 syntax? A. Two methods can be applied to interlaced video that maintain syntactic compatibility with MPEG-1 (which was originally designed for progressive frames only). In the field concatenation method, the encoder model can carefully construct predictions and prediction errors that realize good compres
