How do I record MineCraft smoothly with OBS?

I record videos for YouTube, and I have a laptop that's somewhat crappy. It is an i3 Intel processor. The CPU is always high when I try to record videos. When I am playing a game, the game runs extremely smooth, but when I go back to edit the footage, it is either just me talking or lots of stop motion. Also, on another topic, how do I separate audio from recordings? Any answers that you can answer soon. I would like to start recording today. Thank you for your time.

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