I’m no avid coder and got this info 3rd hand maybe you can make sence of it.
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What you are trying to do is an instant replay mechanic. The intended system to use for the demorec for that specific application is the “FInMemoryNetworkReplayStreamer”. You can specify which streamer to use in your .ini file for your game. You will want to look at “TimeBufferHintSeconds” which is the amount of recording to keep in your memory that is “rewindable”.
That is the best quickstart I can give on the subject. There is not much documentation to search beyond reading through the code. They are releasing documentation from the docteam sometime soon on it."
If you get somewhere with it I’m looking to replay last 10 seconds on an event in multiplayer myself.