If you want to make your video file that bit smaller whilst retaining its quality here is how with FFmpeg. Be aware that compressing video uses a lot of CPU. The more cores and speed (Ghz) of your CPU the better.

The two factors with FFmpeg that will best determine your output size is the -preset and -crf

Preset is the encoding to compression rate, The slower = better compression and therefor more quality in a smaller size. The slowest FFmpeg -preset is veryslow followed by slower and then slow.

CRF means constant rate factor, essentially it is the bitrate amount without it being specific. Lower value = higher quality. 0 is lossless but a value of 17 or 18 is still visually lossless. 21 or 22 i find to be best but once you start going above 25 the quality drops away.

To put it into one command something like this will take time but give a really good compress:

ffmpeg -i inputfilename.mp4 -c:v libx264 -preset veryslow -crf 21 outputfilename.mp4

Or for something a little quicker:

ffmpeg -i inputfilename.mp4 -c:v libx264 -preset slower -crf 22 outputfilename.mp4

To maximise your FFmpeg usage look into getting a dedicated server, You will be able to run these multi core tasks faster.