How to Compress a Video Without Losing Too Much Quality

Compressing without losing quality is not quite possible, and any tool promising it is being loose with the truth. What is possible is losing so little that nobody notices, and the difference between a good compression job and a bad one at the same file size is enormous. It comes down to knowing which knob to turn first.

Where the quality goes

Video compression works by not storing most of what is in front of it. It stores a full frame occasionally and then describes the changes since, because most of a frame is identical to the one before. Within a frame, it discards detail the eye is poor at noticing, particularly fine colour variation, which we see far less precisely than brightness.

When there are not enough bits to go round, the encoder starts making visible compromises. Blocking appears where flat areas break into squares. Detailed textures like grass, water, hair and confetti turn mushy, because they are expensive to describe and the encoder gives up. Banding shows in gradients such as skies. These are the symptoms of an encoder rationing.

The order to change things

Not all reductions cost the same amount of visible quality. Roughly in order of best value:

1. Trim the length. Size scales directly with duration and cutting dead air costs nothing visually. Thirty seconds removed from a two minute clip is a quarter of the file gone.
2. Use a better codec. H.265 or AV1 will reach the same visible quality at roughly half to two thirds the bitrate of H.264. This is the largest free win available, and the only cost is compatibility and encoding time.
3. Drop the resolution, if the bitrate is tight for the size. Going from 4K to 1080p removes three quarters of the pixels, and a clean 1080p beats a starved 4K every time.
4. Lower the frame rate, but only if the motion allows. Sixty to thirty halves the frames. It is fine on a talking head and obvious on sport.
5. Lower the bitrate directly. This is the last resort because it is the change that shows first.

Constant quality is usually the right mode

Most encoders offer a choice between targeting a bitrate and targeting a quality level. The quality mode, often called CRF, lets the encoder spend whatever each scene needs to hit a consistent visual standard: more on the complex parts, less on the simple ones. The result is usually better looking and often smaller than a fixed bitrate at the same average.

The trade is that you cannot predict the file size in advance. If you have a hard size limit, target the bitrate. If you want the best-looking file for the least size, target quality. On the common CRF scale, lower numbers mean higher quality and larger files, and the useful range for most footage sits somewhere in the high teens to mid twenties.

Encoding speed is quality you can have for free

Encoders have a speed setting, often named from very fast through to very slow. A slower setting lets the encoder search harder for efficient ways to describe the same picture. At the same target quality, slower produces a smaller file; at the same bitrate, it produces a better one. Nothing is lost except your time, and on a file you are going to keep, dropping one or two steps slower is usually worth it.

Always compress from the original

Each pass through a lossy encoder throws away a little more, and the losses accumulate. Compressing an already compressed export is how a video ends up looking soft for no obvious reason. Keep the original, and when you need a different size, go back to it.

Checking your work

Do not judge a compressed file scaled down in a preview window. View it at full size and look at the places compression fails first: fast motion, fine texture, dark scenes and smooth gradients. If those hold up, the rest will.

The compression estimator on this site converts your target size into bits per pixel per frame, which is the figure that actually predicts whether a target is realistic for a given resolution. If it comes back very low, no amount of careful settings will save it and the resolution needs to come down.