Xonotic: Video on Demand (VoD)

Then you can replay the demos and it doesn't matter at all if it stutters then - you'll get perfect fps in the video.
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That is what I have explained: with the lags, I can't aim well, so I can't make the great moments happen, so I can't make good video out of it.

Go to the Mu;tiplayer window and in the Demo tag and make sure you have the Demo recording checked. After that each game will be recorded and this demo can be replayed any time through the Demo list.