From speaking with a cable manufacturer (the owner in fact), I learnt that the skin effect is far more pronounced (and beneficial) in video transmission than audio, so silver-plated copper is probably the best combo for video frequencies.
Having said that, Jaybo is right; having done some work years back with television studios, it's copper copper everywhere. Now that was for normal analog transmission, so who knows what TV studios are using for freeview HD digital? Perhaps it's worth finding out, since what the pro's use is a good guide for us.