What is the lightest way computationally to video record rviz

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rosbag record the topics displayed by rviz, then play them back later and if still needed record the desktop with slam no longer running.

Consider adding another computer dedicated to recording, it will be less cpu to send topics over the network than save them locally to disk. rviz itself may be taking a lot of cpu (I see it slow down the most under moderately large point clouds) so having this second computer to observe the output even if it isn't getting recorded isn't a bad idea.