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 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
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.