Unless you’ve got raw uncompressed video, any kind of transparent compression like you describe is only going to cost you in energy bills for no benefit. Most video is already compressed with specialised video compression as part of the file format, you can’t keep compressing stuff and getting smaller files.
The alternative is a lossy compression, which you could automate with some scripts or a transcoding tool like tdarr. This would reduce the quality of the video in order to reduce the file size