These are fortunately very rare and only occur with
DVDs that have been mastered from inferior analogue video tape sources.
These look the same as tracking errors on a home VCR, with horizontal lines
running through the picture causing image distortion. In the case of DVD,
these errors can be disastrous for MPEG encoding, leading to additional
MPEG compression artefacts in the image which magnify and accentuate the
Angel And The Badman (Avenue One) 3:49
Note the tracking error across the middle of the image.