Drop your MP4 file. We'll convert it to MKV right here in your browser, your file never leaves your device.
MP4
to
MKV
Select your file here to get started
or drop your file here.
Accepts .mp4, .m4v
nothing uploaded no file size cap no signup
How it works
Three steps. No upload, no signup.
1
Drop your file
Click the dropzone above or drag a MP4 from your desktop. Files of any size, there's no upload, so there's no upload limit.
2
Convert in your browser
The conversion runs entirely in this tab using JavaScript and WebAssembly. Your file never touches our servers, we don't have any.
3
Download
Get your MKV the moment the conversion finishes. Convert another, or close the tab.
Files stay on your device
Your file is never uploaded. The entire conversion runs in your browser using WebAssembly. We can't see what you convert because we have no server to see it.
No file size limit
Server converters cap free users at 1-2 GB and gate larger files behind a paid plan. Since nothing uploads, our limit is whatever your browser can handle.
Free, no signup, no ads on conversions
No account required. No watermark on the output. No queue. Drop a file, get a converted file.
Formats involved
About MP4 and MKV
MP4, MPEG-4 Part 14
MP4 is the dominant video container on the web, H.264 video plus AAC audio, in a structure designed for streaming. Every browser, mobile device, smart TV, and editing tool reads MP4. The format is technically a container (not a codec), so two MP4 files can have very different internal codecs, but the H.264+AAC default is what enables universal playback.
How to open
Every video player on the planet, VLC, QuickTime, Windows Media Player, browsers (HTML5 video), iOS, Android, smart TVs, game consoles. Universal.
MKV is an open-source container that holds essentially any video/audio codec combination plus subtitles, chapters, and metadata. The format of choice for high-quality video archives, fan-subtitled content, and anything that benefits from multiple audio tracks. The catch: not every player supports it, and converting MKV to MP4 is the standard fix for the won't-play-on-my-TV problem.
How to open
VLC reads everything MKV. Plex and Kodi handle MKV libraries. Browsers and many TVs do not, converting to MP4 makes MKV content universally playable.
Last verified May 2026 from each competitor's pricing and FAQ pages. Limits and pricing change frequently.
FAQ
Common questions
Is this MP4 → MKV converter really free?
Yes. No signup, no watermark, no daily file count limit. Every conversion runs in your browser, your file never touches our servers because there are no servers.
Where does my file go when I convert it?
Nowhere. The conversion runs entirely in your browser using JavaScript and WebAssembly. Your file is never uploaded to our servers. We don't have any servers handling files, there's nothing for us to log, store, or accidentally leak.
What's the maximum file size?
Whatever your browser can hold in memory. Practically, this means a few hundred MB on most computers, significantly larger than the 1-2 GB caps that server-upload converters charge for. Very large files (multi-GB) may require closing other browser tabs first.
Why convert MP4 to MKV?
Web video, mobile video recording, video sharing. High-quality video archives with multiple audio/subtitle tracks. The most common reason to convert is compatibility, MKV works in places where MP4 doesn't, or vice versa.
How do I open a MP4 file in the first place?
Every video player on the planet, VLC, QuickTime, Windows Media Player, browsers (HTML5 video), iOS, Android, smart TVs, game consoles. Universal.
Does this work offline?
Once the page is loaded, the conversion itself runs entirely offline. The first time you use a tool, your browser downloads the conversion library (a one-time cache). If you reload while offline, the page won't load, but you can install the site as a Progressive Web App for full offline use.
Can I convert multiple files at once?
Single file at a time for now. Batch conversion is on the roadmap, for now, drop one file, download the result, then convert the next.