Video file size is mostly a function of one setting: how aggressively the encoder is allowed to discard information the human eye is unlikely to notice. H.264, the codec this tool uses, controls that trade-off through CRF — Constant Rate Factor — a single number from roughly 0 (lossless, enormous files) to 51 (unwatchable, tiny files). Rather than targeting an exact bitrate, CRF encoding lets the bitrate float scene by scene: a static talking-head shot needs very little data per frame, while a fast action sequence with lots of motion needs much more, and CRF automatically allocates more bits where the eye would actually notice the difference.
This tool offers three CRF presets tuned for different priorities. High Quality (CRF 23) is the same setting broadly considered visually transparent for most viewers, and typically shaves 20-30% off a file with negligible visible change. Medium Quality (CRF 28) pushes further, usually landing 40-60% smaller with only mild softening visible on close inspection, and is a good default when you need to fit under an upload limit. Low Quality (CRF 35) prioritizes size above all else, often reaching 60-80% smaller, with visible blockiness in high-motion scenes but is still watchable — useful when the alternative is not being able to send the file at all. Every preset re-encodes both video (to H.264) and audio (to AAC) and packages the result as a fast-start MP4.
Combine it with Trim Video to cut unnecessary footage first, or Mute Video if the audio track isn't needed — both shrink the file further before you even get to compression.
