I remember that some 40yrs ago,in a communist Eastern European country where (and when) having a set of Rotosounds was automatically made you the king of the block,a friend of mine made something very similar (the guy tested for 6 or so months various steel cores,materials/diametres as well as different copper wires.The late was Cu-Em, the most usual insulated copper wire used in electrical motors' manufacture and whatnot.
As I recall,the "final" product (strings for 34" necks,4-string set) was very "piano-ish" sounding (a desirable effect at that time

,with loads of sustain and good intonation.Moderate (not high!) output due to the inner strings' structure and composition.
However,these strings had two major drawbacks:first,the copper's outer isolation (email) worn out after a couple of weeks/months and,second,the whole string had some serious dings under,right where it touched each fret (a normal behaviour BUT not so obvious on most steel/nickel wraps)....since copper was softer than any fret's material.
Bottom line:because of the specific,twangy character wich was so sought after at that time,we used alot of those strings at the expense of changing them every 5-6 months or so. Once the "factory recipe" was achieved and the inherent flaws were noted,my buddy made those strings in VERY large quantities.

...eh.....good ol' times.....

PS
AFAIK after watching the video you posted,the guy uses some kind of tinned copper (if the string being made while recording is a copper one,indeed).Also,in the same movie clip I see some reels with coloured wire (green,reddish,etc).Except the shiny,"a-la-nickel" look of the wire that is made during the video recording,all others wires appear to be having the email coloured,translucent isolation.Wich is exactly what it's used in electrical motors and what my buddy used 40yrs ago.(please correct me if I'm wrong).