Free online video compressor that never uploads your files

Rtools Video Compressor reduces video file size directly in your web browser. Because it uses ffmpeg compiled to WebAssembly, your video is processed on your own computer — there is no upload, no waiting in a queue, no watermark and no sign-up. Compress MP4, MOV, MKV, AVI or WebM files to an exact size in megabytes, to a percentage of the original, or to a chosen quality level.

How to compress a video

  1. Add your video. Drag and drop a video file onto the page, or click to browse. The file is read locally and never uploaded.
  2. Choose a compression method. Target a percentage of the original size, an exact size in MB, a quality level (CRF), a smaller resolution, or a maximum bitrate.
  3. Adjust quality and format. Pick H.264 or H.265, set the encoding speed, choose an output container, and add subtitles if you need them.
  4. Compress and download. Click Compress Video, watch the live progress, then download the finished file and compare it against the original.

Why use this video size reducer

100% private — nothing is uploaded

Encoding runs on your own machine through ffmpeg.wasm. Your footage never touches a server, so there is no upload time, no queue and no file retention to worry about.

Hit an exact target size

Need to fit under 25MB for Discord, 10MB for email or a strict upload cap? Enter the number and the bitrate is calculated from your video duration to land on it.

Real codec control

CRF, encoder preset, maximum bitrate, resolution, H.264 or H.265/HEVC, and an old-device compatibility mode — the settings a real encoder exposes, not a single vague slider.

Subtitles, burned in or soft

Upload an SRT or ASS file and burn it permanently into the picture, or keep it as a switchable track. Existing subtitle tracks can also be copied across.

No watermark, no sign-up

No account, no email, no watermark stamped across your video, and no paid tier holding the useful settings hostage.

Wide format support

Reads MP4, MOV, MKV, AVI, WebM, WMV, FLV, TS, MPG, 3GP and more. Writes MP4, MKV, MOV, AVI or WebM.

Frequently asked questions

How do I reduce the file size of a video?

Drag your video onto the page, choose how you want to compress it — a percentage of the original size, an exact size in MB, a quality level (CRF), a smaller resolution, or a maximum bitrate — then click Compress Video. The compressed file is ready to download when encoding finishes.

Are my videos uploaded to a server?

No. Compression runs entirely inside your browser using ffmpeg compiled to WebAssembly. Your video never leaves your device and is never sent over the network, which also means there is no upload wait and no file retention.

Is this video compressor free?

Yes. There is no charge, no account, no watermark and no file limit imposed by us. Because the work happens on your own computer, there are no server costs to pass on.

Which video formats are supported?

Input: MP4, MOV, MKV, AVI, WebM, WMV, FLV, TS, MPG/MPEG, 3GP, M4V, OGV and most other common containers. Output: MP4, MKV, MOV, AVI and WebM. Video is encoded with H.264, H.265/HEVC or VP9, and audio with AAC or Opus.

How do I compress a video to a specific size, like 25MB for Discord or email?

Choose the "Target a file size (MB)" method and enter your limit — for example 25MB for Discord or 10MB for a Gmail attachment. The required video bitrate is calculated from your video’s duration so the finished file lands at or under that size.

How much can I compress a video without losing quality?

Most videos can be reduced by 50–70% with little visible difference, especially screen recordings and phone footage, which are often encoded inefficiently. For quality-first results use the CRF method: 18 is close to visually lossless, 23 is a balanced default, and values above 28 begin to show artefacts.

What is CRF and which value should I use?

CRF (Constant Rate Factor) keeps perceived quality constant instead of bitrate, spending more data on complex scenes and less on simple ones. The scale runs 0–51, where lower means better quality and a larger file. 23 is the default; try 20 for higher quality or 28 for a much smaller file.

Should I use H.264 or H.265?

H.265/HEVC produces roughly 25–50% smaller files at the same quality, but encodes noticeably slower and is not supported by some older devices and browsers. Choose H.264 for maximum compatibility, H.265 when the smallest file matters more than encoding time.

Why does resizing make the file so much smaller?

File size scales with pixel count. Dropping a 4K video to 1080p removes about 75% of the pixels, so the same visual quality needs far less data. If your footage will only ever be watched on a phone or a 1080p screen, downscaling is the single most effective way to shrink it — and it is also the fastest to encode.

Does it work on mobile?

It runs in modern mobile browsers, but phones have much tighter memory limits than desktops, so large or high-resolution videos may fail. For long 4K clips a desktop browser is far more reliable.

Is there a file size limit?

There is no limit set by us, but the browser caps how much memory a page may use (around 3GB here). Very large or long high-resolution videos can exhaust it. Lowering the output resolution greatly reduces memory use and is the best workaround.

How long does compressing take?

Browser encoding is slower than a native desktop app because it runs in WebAssembly. A one-minute 1080p clip typically takes a couple of minutes. You can speed it up considerably by choosing a faster encoding preset or a lower output resolution.