What's the best way to reduce video file size?

The three most effective levers are: (1) lower resolution — going from 1080p to 720p cuts size roughly in half; (2) lower FPS — dropping from 60 to 30 fps saves ~40%; (3) lower bitrate — this reduces quality but dramatically reduces size. SuperMotion lets you control all three.

How much can I compress a video without losing quality?

For most videos, reducing bitrate by 30–50% is barely noticeable on a screen. Reducing resolution is more visible but often acceptable. Experiment with small decrements and preview the result.