WEBM to MKV converter
Convert WEBM to MKV in seconds, free and unlimited. No upload, no sign-up, no watermark: your video never leaves your device.
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Quick answer: To convert WEBM to MKV, add the WEBM file to the iHateFiles WEBM to MKV converter and press Convert. The conversion runs in your browser, so the file is never uploaded, and it is free with no sign-up, watermark or size limit. Re-encodes the picture and sound into a MKV container.
Should you convert WEBM to MKV?
Do this when something specifically needs MKV. The picture is re-encoded, so it costs a little quality; if all you need is a file that plays everywhere, MP4 is usually the better target.
The picture is re-encoded
A WEBM usually holds VP8, VP9 or AV1 video with Vorbis or Opus sound. This writes H.264 video with AAC sound into the MKV. Both sides are compressed with loss, so this is a second generation: leave the quality at its default or higher, because the encoder is working from WEBM artefacts rather than the original.
Where the MKV will play
MKV plays on VLC, Plex, most smart TVs and Android, but not the iPhone Photos app or QuickTime.
WEBM and MKV side by side
| WEBM | MKV | |
|---|---|---|
| Inside the file | VP8, VP9 or AV1 video with Vorbis or Opus sound | H.264 video with AAC sound |
| Compression | Lossy | Lossy |
| Carries sound | Yes | Yes |
| Plays on | every modern browser and Android, but not QuickTime or older iPhones | VLC, Plex, most smart TVs and Android, but not the iPhone Photos app or QuickTime |
| Here | Read and write | Read and write |
What usually goes wrong
About the WEBM. A browser screen recording is usually a WEBM with a broken duration, so players show it as zero seconds or refuse to seek. Converting it to MP4 rewrites the header and fixes the seeking.
About the MKV. MKV and WEBM share a signature because WEBM is a restricted Matroska, so tools sometimes report one as the other. What matters is the codecs inside.
How to convert WEBM to MKV
- Add your WEBM file. It is read from your disk and stays there.
- Check the settings. The output format is already set to MKV.
- Press convert and the MKV file is saved back to your device.
Questions
How do I convert WEBM to MKV?
Open this page, add your WEBM file, and press convert. The file is decoded and re-encoded by your own browser and saved back to your device. Nothing is uploaded.
Is this WEBM to MKV converter free?
Yes, completely. There is no account, no sign-in, no watermark and no daily limit, because there is no server doing the work. Your own device does it.
Are my files uploaded anywhere?
No. There is no upload endpoint. The conversion runs inside this browser tab, so your file never leaves your device. You can open your browser's network panel and watch: nothing carrying your file is sent.
Is there a file size limit?
No fixed limit. Because the work happens on your machine there is no server quota. The only ceiling is your own device's memory, which for video means very large files may be slow.
Will converting to MKV lose quality?
MKV is a lossy format, so some detail is discarded. The quality control on this page decides how much. The default is set high enough that most people cannot see the difference.
Can I convert several WEBM files at once?
Yes. Add as many as you like and they are converted one after another, then offered as a single ZIP.