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Vob files from DVDs shouldn't have black bars. They should be native widescreen. This should be true for almost all DVDs except the very first ones that weren't anamorphic. If they do have bars for some reason, you could crop them off with ffmpegX.
 
well it's stuff recorded from tv, i have a 4:3 tv and the broadcast was in widescreen, so it recorded the black bars as well
 
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