generate questions: In addition, recording and reproducing an HDTV signal was a significant technical challenge in the early years of HDTV (Sony HDVS). Japan remained the only country with successful public broadcasting of analog HDTV, with seven broadcasters sharing a single channel.
How many broadcasters did Japan have sharing a single channel? {sep_token} Which country had successful public analog HDTV broadcasting? {sep_token} What was particularly challenging in the early years of HDTV? {sep_token} What accomplishment in early HDTV did Japan have?