How to compress a video without ruining the quality

You cannot shrink a video for free: smaller means less data, and less data means some loss. But you can choose what to give up. This guide explains what controls file size and how to trade it off so the result still looks good.

What decides the file size

Size is bitrate times duration. Bitrate is how many bits are spent on each second of the video. If you know your size limit and your video length, you already know your budget.

  • 10 MB over 30 seconds is about 2.7 Mbps in total.
  • 10 MB over 60 seconds is about 1.3 Mbps.
  • 25 MB over 60 seconds is about 3.3 Mbps.
  • 50 MB over 120 seconds is about 3.3 Mbps.

Bits per pixel: is the budget enough?

What matters for sharpness is how many bits each pixel gets per frame. Divide the video bitrate by width, height and frame rate. As a rule of thumb, below roughly 0.05 bits per pixel the picture starts to look blocky and smeared, and above about 0.08 it usually looks clean. The compressor uses these numbers to warn you before you start.

What to give up first

  • Duration. Trim anything you do not need. Every second removed gives the remaining seconds more bits, with no visual cost at all.
  • Resolution. Going from 1080p to 720p cuts the number of pixels to about 44 percent, so the same bitrate looks much cleaner. On a phone or in a chat window the difference is hard to notice.
  • Frame rate. Dropping from 60 to 30 fps halves the frames. It is fine for most talking, tutorials and screen recordings, but fast gameplay loses some smoothness.
  • Audio. A short clip needs little: stereo AAC at 96 kbps is usually fine, and 64 kbps mono saves a bit more when every kilobyte counts.

Screen recordings versus camera footage

A screen recording with a mostly still desktop is easy to compress: most of each frame is identical to the last one. Footage from a camera, with noise, grass, water or fast pans, needs far more data for the same sharpness. That is why two videos of the same length can end up at very different quality with the same size limit.

Mistakes that cost quality

  • Compressing a file that was already compressed. Start from the original whenever you can.
  • Forcing a large resolution into a tiny size. A smaller picture with enough bits beats a big picture starved of them.
  • Upscaling. Enlarging a video never adds detail and wastes bits.
  • Setting a fixed quality and hoping it fits. Working from the size limit backwards, as this tool does, is more reliable.