Regarding NSU, to this day I've failed to figure out how they dubbed their pink panther video with what sounds like the original German dub voice and made it so

Regarding NSU, to this day I've failed to figure out how they dubbed their pink panther video with what sounds like the original German dub voice and made it sound good. Searching on the internet is hard because it finds all kinds of irrelevant stuff. Would like to know more and if this is easily possible for extremists with laptops to accomplish in such seamless quality, if it's a stitch-work of existing audio tracks. It's the same level of quality as the Obama video+audio stitch-work in Mr Robot.