Yes, there's a big difference between the signal coming from the graphics card and one from a video IO card. One is a computer signal, and the other is a broadcast TV style signal. Color space is different, for one. Another, computer signals don't do interlacing well, while the broadcast signal does. So if you edit an interlaced source, you'll need that. But then your display ALSO needs to be able to deal with the proper color space and interlacing, and few computer displays do that.
Shane
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