104 Can motion vectors be used to determine object velocity? (MPEG-2)
Description
This article is from the MPEG FAQ, by Frank Gadegast phade@cs.tu-berlin.de with numerous contributions by others.
104 Can motion vectors be used to determine object velocity? (MPEG-2)
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.
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