Free MKV to WEBM Converter: No Sign-up, Files Never Uploaded
Turn MKV files into WEBM for free, with no sign-up and no upload. The conversion happens in this tab, so your files never leave your computer or phone.
The video and audio tracks are read, decoded and encoded again for the WEBM container, which takes real work from your processor. WEBM uses lossy compression, so each save trades some detail for a smaller file.
This pair runs on code that is already in the page, so there is no extra engine to download.
- Free
- No sign-up
- Never uploaded
- No watermark
Your files are converted on your device and never uploaded.
How to convert
- Add your MKV files by dragging them onto the converter or by using the file picker.
- Check that WEBM is the selected target format; it is already chosen on this page.
- Open the options if you want to change resolution, frame rate and quality, or keep the defaults.
- Press Convert and watch the progress shown for each file.
- Download each result, or take them all together as one ZIP when you converted several files.
Features
- Reads .mkv and writes .webm.
- Free, with no watermark added to the result.
- No sign-up and no login.
- Your files are never uploaded and never leave your device.
- Batch conversion with a ZIP download for several results.
- The input is recognised by its content, not only by its file name.
- WEBM keeps transparency where the source has it.
Supported formats
About the formats
About MKV
Matroska: an open container that holds any number of video, audio and subtitle tracks.
Popular for downloaded films; many TVs and phones cannot play it natively.
About WEBM
Open, royalty-free format from Google, usually VP9 or AV1 video with Opus audio.
Plays in all major browsers.
Can carry an alpha channel with VP9.
MKV vs WEBM
MKV does not support transparency, and WEBM does.
MKV files use the .mkv extension and WebM files use .webm, so the converted file gets a new name with the new extension.
Privacy: how it works
- Your MKV files stay on your device. The page reads each file with the browser's file API, converts it with code running in the tab, and hands the result back as a download. No upload happens, so there is no copy of your file on our servers to protect, delete or leak.
- There is nothing to sign up for and no login. The converter does not ask for an email address, and it does not need to know who you are to do its job.
- You can check the claim yourself: open your browser developer tools, watch the Network tab while a file converts, and you will see no request that carries your file.
Tips
- Try a short clip first to check quality and size before you convert a long video.
- Keep the original resolution unless you need a smaller file; shrinking the frame is the quickest way to cut size.
- Close other heavy tabs while converting, because the work uses your own memory and processor.
- Convert one large file at a time on a phone or a low-memory computer.
- WEBM uses lossy compression, so each save trades some detail for a smaller file.
Frequently asked questions
Is it really free?
Yes. There is no price, no trial, no credit card and no watermark added to your results. Ulkaa Tool does the conversion with your own device, so there is no server bill to pass on to you.
Are my files uploaded?
No. Your MKV files are read and converted inside your browser and are never sent to Ulkaa or to anyone else. The result is created on your device and you save it from there.
Do I need an account?
No. There is no sign-up and no login. Open the page, add your files and convert. An Ulkaa account is not needed for anything on this tool.
Is there a file size limit?
No limit is set by us. The real limit is your device: the conversion uses your own memory and processor, so very large files can be slow or fail on a weak phone or an older computer. Close other heavy tabs and convert MKV files one at a time if a big batch struggles.
What is the difference between MKV and WEBM?
MKV does not support transparency, and WEBM does. MKV files use the .mkv extension and WebM files use .webm, so the converted file gets a new name with the new extension.
Can I convert many MKV files at once?
Yes. Add as many files as your device can handle. Each one is converted on its own and you can download them one by one or as a single ZIP.
Will anything be lost when I convert MKV to WEBM?
WEBM uses lossy compression, so each save trades some detail for a smaller file.
Can I convert WEBM back to MKV?
Yes. Open the WEBM to MKV page and use the same steps. Converting back does not undo any loss from the first conversion.