Massive fps drop while recording

[xylcro]

So when I record a game I get massive fps drops, not the game itself but the video, it goes from 70 to 24-23, with all games, even with Minecraft where I get a steady 120 fps while playing, but the video only gets 24 fps for some reason. My pc can should be able to handle it: intel i7-4470k, 16gig ram, gtx 980, 240 ssd and 3tb wd black, I don't know what it is but it's bugging me. I use very normal settings, lagarith codec (64bit) lame codec for audio, 1080p@60fps (not synced and not locked), file output-avi, thread priority: high (normal or highest makes no diffrence), write speed to ssd:307mb/s, write speed to 3tb wd:166mb/s.
what is the problem here?

Thanks

[ExKoder]

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