There are multiple DVD sets which are noticeably different from one another. The original DVD sets sold in the U.S. and Canada were released under license from NBCUniversal by Imavision Distribution, a company based in Quebec. A majority of the episodes in the original North American DVD versions had scenes cut from the episodes—these were derived from the syndicated television versions by Worldvision Enterprises, the series' former distributor. Other episodes were time-compressed and are NTSC-converted video prints from UK PAL masters, while others were derived from 16MM syndication prints, also from Worldvision. Only a handful of episodes in the original sets were in their original uncut versions. The episodes in these original sets are also known to have relatively poor video quality, such as tracking lines, as well as audio problems, though the quality issues are not as pronounced in the first few seasons as they are in the later seasons. The first three seasons of the old sets notably are also missing closed-captioning.