How to reduce a video's file size

File size is bitrate times length

Bitrate is how much data each second of video uses. Multiply it by the length and you get the file size. A 2 minute video at 8 megabits per second is about 120 MB; at 2 megabits per second it's about 30 MB. Every way of shrinking a video either lowers the bitrate or shortens the video.

The four levers

1. 1.Bitrate: the biggest lever. Lowering it shrinks the file in direct proportion. Too low, and fast motion turns blocky.
2. 2.Resolution: a smaller picture needs fewer bits to look good. 1080p to 720p cuts the pixels by more than half, so a lower bitrate still looks clean.
3. 3.Length: trimming to the part that matters is the only change with no quality cost at all.
4. 4.Audio: speech sounds fine at 96 to 128 kbps. Dropping audio entirely saves a little more, if you don't need it.

Pick a target size, not a quality number

If you're sending to a platform with a limit, start from the limit. Okaysize works out the bitrate that lands just under it for your video's length, then checks the result and runs again slightly lower if it overshoots. You get the best quality that fits, without trial and error.

Use a format that plays everywhere

MP4 with H.264 video and AAC audio plays on practically every phone, computer and app. Newer codecs can be smaller at the same quality, but not every device can play them. For sending, compatibility matters more than the last few percent.

What won't help

• Raising the frame rate or resolution of a small video never adds detail. It only adds size.
• Compressing a video that's already heavily compressed, like one saved from a messaging app, saves little and costs quality. Okaysize tells you when this happens and offers the original back.