It uses ffmpeg open source library.

FFmpeg compresses videos by:

* Choosing a codec: This determines how the video is encoded (e.g., H.264, HEVC).

* Reducing resolution: Making the video smaller (e.g., from 1080p to 720p).

* Lowering frame rate: Showing fewer frames per second.

* Adjusting bitrate: Controlling the amount of data used per second.

* Using keyframes: Storing complete frames less often.

* Quantizing colors: Reducing the number of colors in each pixel.

* Analyzing motion: Finding and removing repeated information.

By combining these techniques, FFmpeg can make videos smaller while maintaining good quality.