Compress video

How the size target works

A video file is its bitrate, the amount of data per second, multiplied by its length. So when you set a limit, the compressor works out a bitrate: it takes 93 percent of the limit as a safety margin, sets aside room for the sound, and divides the rest by the length of the video. Hardware encoders do not always hit a bitrate exactly, so it checks the finished file and, if it came out too large, encodes again with a corrected bitrate, up to three passes in all.

The length of the video therefore decides the quality you can get. These are the video bitrates the compressor aims for with 128 kbps sound:

What those bitrates look like

In our tests a 10 second clip of full HD camera footage used about 3.6 Mbit/s at the Balanced setting. Squeezed to 1.5 Mbit/s with a size target, it scored exactly the same as the 720p version, and fine texture such as trees went soft. A full HD screen recording of an app needed less than 0.8 Mbit/s at every setting, because most of a screen does not change from one frame to the next.

As a rough guide for camera footage: around 3.5 Mbit/s looks like Balanced at 1080p. Near 1.5 Mbit/s, 1080p and 720p look the same, so choose 720p if the video is for phones. Well below 1 Mbit/s detail suffers whatever you choose, and cutting the video shorter with the video trimmer helps more than any setting. Screen recordings, slides and talking heads in front of a plain wall get away with much less. All the measurements are in how to compress a video.

Resolution, frame rate and sound

• Resolution helps when the bitrate is low: fewer pixels share the same data. At 720p a video is meant for phones and small windows; keep 1080p when text on screen must stay readable.
• Frame rate barely changes the size, since the budget is set per second. Halving 30 frames per second to 15 saved only 4 percent in our test. Lower it for slides or very small targets.
• Sound at 128 kbps takes about 1 MB per minute. For speech, 64 kbps is plenty, and for a screen recording without narration, remove the audio and give its share to the picture.

MP4 or WebM

MP4 with H.264 plays on every phone, computer, television and messaging app, so it is the right choice for anything you send. WebM with VP9 came out about a quarter smaller than MP4 at the same quality setting in our test, with slightly lower scores, and plays in every current browser. Use it for video on a web page you control.

If something goes wrong

• The result says it is above the target. The limit is too small for the length at this resolution. Choose 720p or 480p, remove the sound, or trim the video.
• It is slow. Encoding runs on your own computer or phone, and it stops if the tab is closed. Our 10 second full HD clip took about 17 seconds at 1080p and 8 seconds at 720p, so a lower resolution also makes it faster.
• The browser says it cannot do this. The compressor needs WebCodecs, the video encoders that Chrome, Edge, Safari 16.4 or newer and Firefox 130 or newer provide. Update the browser or try another one.
• The file came back unchanged. It was already under the limit, or, with a quality setting, the original was smaller than anything the compressor could make. The original is the better file then.

How we tested. Bitrates in the table come from the compressor's own formula. Quality figures are from our video compression tests: 10 second clips at 1920 by 1080 and 30 fps, encoded with this tool in Chrome and scored with SSIM against the original frames.