Compress Video

A video file is mostly a long list of compressed pictures. How large it is depends on three numbers: how long it runs, how many pixels each frame has, and how many bits the encoder spends on each of those pixels. A phone records generously; a messaging app or an upload form wants far less. This tool re-encodes the video in your browser at a bitrate you choose by quality or by target size, with options to reduce the picture and the frame rate, and it tells you what it achieved.

How the bitrate is chosen

In quality mode the bitrate is the number of pixels per second times the bits spent per pixel. For a 1920 × 1080 picture at 30 frames per second there are 62.2 million pixels a second; at the Medium setting of 0.10 bits per pixel that is 6,220.8 kbps, at High (0.15) 9,331 kbps and at Small file (0.06) 3,732 kbps. A ten-minute video at Medium with 128 kbps sound is therefore (6,220.8 + 128) × 1,000 × 600 ÷ 8 = 476 MB. The three values are rules of thumb for H.264, not guarantees: busy footage needs more.

Target size mode

Choose A file size and enter the megabytes. The bitrate is derived from the size, the duration and the audio: bits available divided by seconds, minus the audio bitrate. For a 120-second video aiming at 25 MB with 128 kbps sound, 25,000,000 × 8 ÷ 120 ≈ 1,666.7 kbps in total, leaving 1,538.7 kbps for the picture. If that leaves less than 150 kbps the page warns that the picture will be very blocky. Encoders do not hit the target exactly, so aim a few percent low.

A worked example

Press Sample to record a three-second 320 × 180 test clip with sound, then press Compress with the defaults (Medium, 30 fps limit, original size). The page re-encodes the clip frame by frame and offers an MP4 whose size is shown with its share of the original. A tiny clip like this can come out larger or smaller than its source, because the source was recorded by the browser’s own real-time encoder; this is why the comparison is shown. Real videos from phones are normally much larger than the Medium result.

Reducing size and frame rate

Scaling a 4K video to 1080p cuts the pixel count by four before any compression, and is the biggest single saving. Lowering 60 frames per second to 30 halves the data again. The Remove the sound switch saves the 128 kbps of audio, which for a short clip with a low video bitrate is a noticeable share. Only reduce the frame rate for content that does not need smooth motion, such as a screen recording.

Edge cases

Very high resolutions need an encoder level the browser supports; if H.264 at that size is unavailable the tool says so and suggests WebM or a smaller size. The progress bar covers audio first, then each frame, and you can cancel at any time. Interlaced or variable-frame-rate sources are sampled at constant intervals. HDR is not preserved.

Limits

Re-encoding is lossy: some quality is lost even at High, and a source that was already heavily compressed can grow. Processing time grows with length, size and frame rate. The tool does not trim, crop or change the aspect ratio; use the cutter for trimming. Everything runs on your device.

Related tools

• Video File Size Calculator plans bitrates and sizes before you compress.
• Video Cutter & Trimmer shortens the video first.
• WebM to MP4 Converter changes the container and codec only.
• Mute Video removes the sound track.