I have recorded several videos in OBS. I then remux them in OBS to .mp4 files.
For example, I have one right now that is recorded in 4k at 60fps and is 1 hour 11 minutes long. It is 4.1gb.
I edited it down to 21 minutes by speeding up and cutting out some sections.
When I export it, it goes from 4k to 1080 if I choose "Match Sequence Settings". I would like to keep it in 4k but this isn't the biggest issue. The issue is it goes from 4.1gb to 14gb. Quality worsens and yet the file size is 10x greater.
I have tried exporting in other formats. If I use AVI and go down to 720 it is still 10gb.
It should be smaller than the original file, not larger. It is much shorter in length and much worse in quality.
To lower the file size of the exported media, use any of the compressed Formats like HEVC(H.265). Also, lowering the Target Bitrate and a smaller resolution can help reduce the file size. Hope this helps. Let us know if you have any questions.