Compressing mp4 files is a waste of time, and won't solve your memory problem. You'll waste a lot of time and compute power for nothing. Compressing files to save memory, only works for specific types of files. 7z or winzip are mainly used now to take a group of files and contain them into a single file.
To solve your memory problem, you're going to need to do 1 of 2 things (or both).
- Buy another hard drive. OR replace your current drive with a bigger one.
- Re-encode the files to reduce the file size.
Around 20000 kbps datarate and bitrate
This is an extremely high bitrate for a video.
Typically most 720p videos have a bitrate of 2000-4000 kbps.
1080p videos will typically have a bitrate of 4000-8000 kbps.
4k files 8000-16000 kbps.
In my humble opinion, anything over 8000 kbps (for 720p/1080p) is a waste of memory space for the average video. Because it becomes increasingly difficult to visually tell the difference between 8000 kbps and 20000 kbps or 50000 kbps. But of course that line of reasoning only applies to typical TV sizes. IF you own a 75+ inch TV, you might start to see a difference.
You could re-encode the files to H.265 as well, and that would also reduce the space while keeping the image quality high.
Re-encoding files can be done using a free piece of software called Handbrake.
So both methods are going to cost you time and more importantly money.
Buying a hard drive = $$$
Encoding your files to a smaller bitrate is going to increase your CPU usage to 100% and take hours upon hours depending on how many files you have. Test 1 of your files to reduce down to let's say 8000 kbps. Record that time and multiply it by how many files you have. All that time = electrical power, and electricity costs money. Not only that, you will also possibly be reducing the quality of your video in your eyes.
Buying another hard drive is the cheaper of the 2 method, because of how cost effective memory is now. But it's up to you how to solve the issue. But compressing video files is a complete waste of time and CPU power.