How do I convert WebM to MKV?

Add your WebM file to the upload area above, then press Convert. The MKV file downloads straight to your device. You do not need an account, and there is no watermark.

Are my files uploaded to a server?

No. This conversion runs entirely inside your browser using WebAssembly, so the file never leaves your device — you can even disconnect from the internet after the page loads and it will still work.

Does converting to MKV reduce quality?

MKV uses lossy compression, so some data is discarded. At the default quality the difference is very hard to see or hear; raise the quality setting if you need to be certain, at the cost of a larger file.

How large a file can I convert?

Up to 512 MB per file for this conversion. Because the work happens in your browser, the practical limit is your device's memory — larger files work on a desktop with plenty of RAM and may fail on an older phone.

Can I convert several files at once?

Yes. Add as many as you like and press Convert All. Each file is processed independently, so one failure does not stop the rest, and you can download everything together as a ZIP.

Can I use this on my phone?

Yes. FileTools360 works in mobile browsers on iOS and Android, including choosing files straight from your camera roll. Very large videos may run out of memory on a phone — those are better converted on a laptop.

VideoAdjustable qualityRuns in your browser

WebM to MKV Converter

Turn WebM files into MKV in a couple of clicks. Open, royalty-free container built for the web. Flexible container that holds any codec, subtitles and tracks. The output is re-encoded, so quality depends on the settings you choose.

On your deviceNever uploadedGone when you close the tabHow this works

Drop your files here

WebM files (.webm) · up to 512 MB each

or paste files from your clipboard

Ready when you are

Drop a WebM file above and FileTools360 will turn it into MKV — right here on your device, without uploading anything.

⌘K to search converters

How to use it

1
Add your WebM files
Drag them onto the upload area, choose them from your device, or paste them from your clipboard. You can queue several at once.
2
Adjust the settings if you want to
The defaults suit most people. Open Advanced to control codec, resolution and bitrate, the audio track and start and end times.
3
Convert and download
Press Convert. Everything happens on your own device — nothing is uploaded. Download files one by one, or grab them all as a ZIP.

WebM and MKV explained

WebM is an open, royalty-free container built for the web, holding VP8/VP9 or AV1 video with Vorbis or Opus audio. It exists specifically so browsers can ship video support without patent licensing.

Matroska is a container designed to hold essentially anything: any codec, unlimited audio tracks, subtitle tracks, chapters and attachments in one file. It is the format of choice for archiving films with multiple languages.

Where WebM files come from: Web video, and exports from browser-based recording tools.
Where MKV is used: Media archives, anime and film collections, and high-quality recordings.

WebM vs MKV

The two formats solve different problems, which is why converting between them involves trade-offs rather than a straight upgrade.

WebM compared with MKV
Property	Source	Target
Compression	Container (depends on codec)	Container (depends on codec)
Animation	Yes	Yes
Introduced	2010	2002
Browser support	All modern browsers. Weak native OS support.	Great in VLC and media servers, poor in browsers.

WebM is stronger at: Royalty-free with no licensing obligations. Smaller than H.264 MP4 at similar quality. Supported by all modern browsers.
MKV is stronger at: Holds any codec. Unlimited audio, subtitle and chapter tracks. Open and well documented.

Why convert WebM to MKV?

People make this switch when they run into the limits of WebM: sharing files with people who will open them outside a browser. MKV is the better fit when archiving or watching in a capable player such as VLC or a media server.

WebM limitations that prompt the switch: Poor support in desktop players, editors and on TVs. Slower to encode than H.264. Not accepted by many video platforms as an upload format.
What you give up: Browsers will not play it. Many TVs, phones and editors reject it.

Does converting WebM to MKV reduce quality?

Both formats store the content without discarding data, so this conversion preserves it exactly. The file size may change because the two formats compress differently, but the content itself is unaffected.