Reddit mentions of S-Video AV Cable [SNES/N64/GAMECUBE]

I find it much easier to just use one of these. This splits the signal for you straight out of the console, so you can plug S-video into the capture card and the composite end into the TV. You can then split the audio if you want, or put one audio channel into the TV and one in the card (in which case you'd have to make sure the audio is mixed to both channels), or both into the card (in which case you'd have to listen through your capture program). I do the latter.

I can give you some sample videos of what this looks like, recorded with Amarec/LAGS codec. For such a simple set of equipment you get about as good of quality as you're going to get out of a normal N64.

If you're in Europe, Scart is by far the best choice. It offers excellent video quality compared to what you get from RCA cables. However, if you are not in Europe, it is unlikely that your TV will support Scart. The next best option would be an S-Video cable which can be used with the majority of TVs in North America and other regions. It is a large step up from the signal carried over RCA, but it is not good as Scart. I use this one for my SNES: https://www.amazon.ca/Tomee-S-Video-Cable-Nintendo-GameCube/dp/B00HRJWCBC