Resolution is the real compressor
File size scales with pixel count, so halving a video's width roughly quarters its size — before any quality tricks. That makes resizing the most effective single step for getting a clip through chat apps, email limits and slow uploads: a phone-shot 4K video at 720p is typically a tenth the size and looks identical on the screen it will be watched on.
The aspect ratio always follows the width — nothing is stretched — and the tool never upscales, because adding pixels adds size without adding detail. Encoding runs on FFmpeg in your browser at roughly real-time speed; the video never uploads. To squeeze further at the same resolution, the Video Compressor works the quality axis instead.