Question / Help Filters: Render Delay vs. Video Delay

I need to put some delay in my capture card to sync it to the webcam, and there's two options in the filters.
What's the difference between these two?

Also I'm getting some weird framerate drop in this card (Avermedia Live Gamer Extreme). It's running fine at 60 fps and it suddenly drops to 30 fps and stays there for 1 or 2 minutes, and goes back to 60 fps. Maybe related to the delay?
 
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