S-Video video capture

What is the best way to capture video from an S-VIDEO source without losing any picture quality or smoothness of motion? What Blackmagic products should I use?

any BMD product that supports Y/C in is fine. ideally use a higher bit rate codec like ProRes 422 or Similar DNxHD setting. A Low bit rate codec may be tempting but with composite dot crawl its seen as detail by the codec so you need to give the codec enough bits to deal with it. if they are camera tapes, they are what they are. if they passed thru composite - switcher, DA, VTR input what's there is what's there. If you find the playback unstable and causing sync ( capture) problems either get a VTR with a built in TBC or you'll need an external one. BMD capture device is really the least of any concerns.