How to use the Compress MKV tool
- Choose your video, or drag it onto the box.
- Pick a quality level, or switch to "Target size" and type the size you need.
- Press Compress video and wait for the progress bar to finish.
- Compare the before and after sizes, preview the result and download it.
About this tool
MKV files from screen recorders such as OBS, or from downloads, can be enormous because they are recorded at high bitrates for editing. Browsers cannot write MKV files, so the compressed video is saved as MP4, which is usually smaller and plays on far more devices.
Choose a quality preset for a quick result, or switch to Target size and enter a limit such as 25 MB. The tool picks the bitrate for you, lowers the resolution automatically if the target is tight, and re-encodes with your browser's hardware encoder. You can also limit the frame rate or remove the audio.
Why use ToolsCrow for this
- Quality or exact size. Two ways to control the result.
- Never bigger than needed. The bitrate is capped by the source.
- Private. Runs on your device.
- No watermark. Free with no account.
Good to know
- The output is MP4 because browsers cannot create MKV files.
- Audio codecs your browser cannot decode (for example AC-3 or DTS) are dropped, and you will be told.
Frequently asked questions
Is my video uploaded to a server?
No. Everything runs inside your browser tab using your own device's video hardware. Your file is never sent to ToolsCrow or anyone else, which also means there is no waiting for an upload and it keeps working if your connection drops after the page has loaded.
Is it really free? Is there a watermark?
It is free with no sign-up, no watermark and no daily limits. The only limits are the ones your device sets: memory and processing power.
How large a video can I use?
Because the video is processed on your device, the limit is your device's memory rather than a server quota. Phone clips of several hundred MB are fine on most devices, and desktop computers usually handle 1 to 2 GB. Files over about 4 GB are not supported.
Which browsers work best?
Current Chrome, Edge and Safari (16.4 or newer, including iPhone and iPad) work best because they include the WebCodecs video engine. Recent Firefox versions work for many files. Older browsers fall back to a much slower real-time mode or may not work at all.
How much can I shrink a video?
Phone and screen-recording footage often shrinks 60 to 90 percent with little visible loss. Videos that were already compressed for the web may only shrink a little.
Why does my result have Opus audio instead of AAC?
Some browsers (for example Chrome on Linux) cannot encode AAC audio. When that happens the tool saves Opus audio instead and tells you. Opus plays in Chrome, Firefox, Edge, VLC and recent Safari; if you need AAC everywhere, run the tool in Chrome or Edge on Windows or macOS, or in Safari.
Why is it fast, or slow, on my device?
Speed depends on whether your device has hardware video encoding, which most phones and laptops from the last several years do. A short phone clip usually finishes in seconds. Very long, 4K or high-frame-rate videos take longer, and the progress bar shows an estimate.
Related video tools
- Video CompressorShrink any video to a fraction of its size while keeping it sharp, or type the exact size you need in MB.
- Compress Video to 25MBReduce a video to about 25 MB without guessing at settings.
- WhatsApp Video CompressorGet a video ready for WhatsApp in one step.
- Video ResizerScale a video down to 1080p, 720p, 480p or 360p and keep the proportions.
- Video ConverterConvert a video to MP4, WebM or MOV without uploading it anywhere.
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