Feature request: Stream logging for replay recording

[kode54]

Is your feature request related to a problem? Please describe.
It would be nice if I could record my gameplay sessions without simultaneously doing a second recording on the server end, or recording the decoded output locally on the client machine.

Describe the solution you'd like
It should be simple enough to support remuxing the video and audio streams on the client side, possibly with the addition of a circular buffer for optionally saving the last 30 or 60 seconds on a hotkey event, or supporting start/stop full logging to disk as a different choice. The FFmpeg library in use should fairly well support feeding the video and audio streams into a muxer for logging either of these ways.

Describe alternatives you've considered
I considered recording by other means, but since I'm using Games on Whales and the Wolf server, I can't exactly stuff OBS into the same container as Steam. I could enable replay recording there, but I don't think the container comes with either PIpeWire or the portals to power it from the integrated Sway compositor.

I could also record locally on the client machine, but then I'd be transcoding it from one format to another, and not necessarily frame locked to the stream.

Additional context
I'm using a streaming server on my LAN, and it would be neat if I could log the video output of the session for later use, or at least have an optional replay buffer mechanism for spinning off highlights. The server is already taking care of encoding video for me. It just needs to be remuxed into a container and saved on the client machine.

I may look into attempting something along these lines, if I can get it building locally on my Mac.