How to reduce video file size

The one equation

A video file is mostly its video bitrate times its duration, plus a smaller audio share. So there are exactly three levers: lower the bitrate, lower the resolution (which lets a lower bitrate still look good), or shorten the clip.

Any tool that promises otherwise is selling something. "AI compression" still moves one of these three numbers.

Lever 1: Resolution

Dropping 1080p to 720p roughly halves the pixels the encoder must describe — so the same bitrate looks much better, or a lower bitrate looks the same. This is why good compressors step down the resolution ladder (1080p → 720p → 480p) instead of starving a 4K frame with a tiny bitrate.

For phone screens and chat apps, 720p is usually indistinguishable from 1080p. For a TV, it isn't — pick the ladder rung for the screen it will be watched on.

Lever 2: Bitrate — exact beats preset

Most tools offer Low / Medium / High and hope the output fits. That is backwards: the platform cares about megabytes, not your quality setting. Start from the number that matters — 20 MB, 50 MB, any exact size — and solve for the bitrate that fits it.

Lever 3: Length

The most underused lever. Cutting 30 dead seconds off a clip saves more size than any quality tweak, with zero quality loss. Trim first, compress second.

And one warning: don't re-compress an already-compressed file repeatedly. Each pass throws away detail you can't get back. Compress once, from the original.

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