Are my WebM files uploaded anywhere?

No. This conversion runs entirely inside your browser, so the file never leaves your device. You can confirm it yourself: open the network tab of your browser's developer tools and convert something. You will see the page load, plus the analytics and advertising the site is paid for with — and nothing carrying your file.

Is converting WebM to MKV free?

Yes. There is no account, no watermark and no limit on how many files you convert — it runs on your own machine, so it costs us nothing to let you. Files up to 100 MB are handled in the browser.

Does converting WebM to MKV lose quality?

MKV is a compressed format, so some data is discarded. At the default setting the difference is not visible; you can raise the quality setting if you need to be certain. Video is re-encoded rather than copied, so some detail is lost even at the highest setting. Subtitle tracks and chapters are not carried over.

Do I need to install anything to open MKV files?

No installation is needed for the conversion itself — it runs in the browser you already have. Opening the MKV afterwards needs whatever software normally handles Matroska Video on your device.

WebMtoMKV

Convert WebM to MKV

Up to 100 files at once. Mixed formats are fine.

You can convert WebM to MKV free and without an account: drop the file above and the MKV is ready to download in a second or two. The conversion happens inside your own browser, so the file is never uploaded — it works on Windows, Mac, Linux, iPhone and Android, and keeps working with the network switched off.

What WebM and MKV are for

The royalty-free web video format. Small files, plays in browsers, ignored by most TVs.

An open container that holds anything — several audio tracks, subtitles, chapters. Weak on hardware players.

How to convert WebM to MKV

Drop your WebM file onto this page, or click to pick one.
Choose MKV as the target. The conversion runs inside your browser — the file is never uploaded.
Download the finished MKV file.

WebM vs MKV: what changes

WebM compared with MKV
	WebM	MKV
Full name	WebM Video	Matroska Video
File extension	.webm	.mkv
Media type	video/webm	video/x-matroska
Compression	Lossy — file size is bought with quality	Lossy — file size is bought with quality

Quality: Some quality is given up for a smaller file. At the default setting the difference is hard to see.
Where it runs: This conversion runs inside your browser. Your file is never uploaded, and it works with the network disconnected.
What can be lost: Video is re-encoded rather than copied, so some detail is lost even at the highest setting. Subtitle tracks and chapters are not carried over.

WebM to MKV: common questions

Are my WebM files uploaded anywhere?: No. This conversion runs entirely inside your browser, so the file never leaves your device. You can confirm it yourself: open the network tab of your browser's developer tools and convert something. You will see the page load, plus the analytics and advertising the site is paid for with — and nothing carrying your file.
Is converting WebM to MKV free?: Yes. There is no account, no watermark and no limit on how many files you convert — it runs on your own machine, so it costs us nothing to let you. Files up to 100 MB are handled in the browser.
Does converting WebM to MKV lose quality?: MKV is a compressed format, so some data is discarded. At the default setting the difference is not visible; you can raise the quality setting if you need to be certain. Video is re-encoded rather than copied, so some detail is lost even at the highest setting. Subtitle tracks and chapters are not carried over.
Do I need to install anything to open MKV files?: No installation is needed for the conversion itself — it runs in the browser you already have. Opening the MKV afterwards needs whatever software normally handles Matroska Video on your device.