Ok, so the quality of the codec determines the quality of the de-interlacing. I have a NVidia EN7300 card so I should use the purevideo decoder, but can't ffdshow do the job right? I try to minimize the amount of codecs on my system...De-interlacing is done by the codec, and if you use the right codec the gfx card help. If you have a nvidia card then nvidia purevideo decoder is recommended. I you have a ATi card Powerdvd codecs are good.
And you say that a good decoder, like purevideo, turns on HW accelleration, right? ...Spragleknas wants to avoid this to prevent IRQ conflicts... I have a Dual Core E6750 so my processor could handle the toughest 1080p movies single handedly without any "extra help".
So what is probeably the better solution in this case?