[Linktothepast]

As others have said, when we don't talk about HDTV but or DVB-tv, like pal and ntsc, the input signal is analog. A computer cannot manipulate the signal in any way, meaning for example saving video on a hard drive, unless it is converted to a digital format that understands. Your question is similar of asking emulating a vinyl music disk in a computer or something. Whenever there is any analog to digital conversion of a signal and vice versa, there is some signal quality loss.