When I got a 12GB+ video file for 4min of 4k, I knew it wasn't right. I used "ffmpeg -i "big rendered file.mp4" "small compressed file.mp4"" and it cut the file to ~3GB. I assume this means the Replay mod outputs videos with full frames, instead of most frames just having data for pixels changed from the last frame. Adding an option for the ffmpeg command to be run post-render to automagically compress the file.
The problem is, that in the command line arguments, the preset is on ultrafast by default, which means, it will be fast, but it will have a huge file size. Try to change it, to an other setting.
Possible presets:
ultrafast,superfast, veryfast, faster, fast, medium, slow, slower, veryslow
