How to compress videos with Quicktime Player
Here's how you use Quicktime to compress your video files:
Open Quicktime Player.
A popup should appear asking you to select your video. If it doesn't, click File > Open File.
Then, click File > Export As…
You'll see a list of video resolutions. Choose the next lowest resolution.
Name your video and choose a location to save it.
Also, To Secure your macOS from virus and trojans, use always a mac optimization software like Mac optimizer.
One of the most popular ways to compress your videos is with the iMovie app. It comes standard with macOS, but if for some reason it's not on your computer, you can download it from the Mac App Store.
After you've found iMovie in your Applications folder or re-downloaded it, follow these steps to compress a video.
Open iMovie.
Click Create New > Movie.
Then, click File > Import and select the video you want to compress.
Your video will appear in the browser window. Drag it into the timeline window.
Click File > Share > File…
Choose your export settings. Adjusting the Resolution and Quality will have the most impact on your file size, but you can also set the Compress dropdown to Faster. Now, click Next.
Name your video and choose where you want to save it. Hit Save.