Convert MP4 to MKV
Free MP4 to MKV converter that runs entirely in your browser. No uploads, no signup required.
Drop MP4 files here
or browse your device. Free, no signup required, no watermarks.
Files are processed on your device, never uploaded
Media conversions run on a full FFmpeg engine compiled to WebAssembly. The engine (~31 MB) downloads once on your first conversion, then everything runs locally.
Three steps
How to convert MP4 to MKV
Add your files
Drop MP4 files into the box above, or click it to browse. Add several to batch convert.
Convert
MKV is already selected as the output. Hit Convert. Your browser does the work locally.
Download
Save each converted MKV file. Pro ZIPs whole batches in one click.
MPEG-4 video
MP4
MP4 is the standard video format that plays everywhere: phones, browsers, TVs, and editing software.
Matroska video
MKV
MKV is an open container that can hold any codec, multiple audio tracks, and subtitles in one file.
Why convert MP4 to MKV?
MP4 is the standard video format that plays everywhere: phones, browsers, TVs, and editing software. MKV is an open container that can hold any codec, multiple audio tracks, and subtitles in one file. Converting from MP4 to MKV gets you the best of the target format wherever MP4 falls short, whether that's compatibility, file size, or what your apps and devices can open. With FormatFusion the switch takes seconds and your files stay on your device the whole time.
Questions
MP4 to MKV: common questions
Is this MP4 to MKV converter free?
Yes. It is completely free with no watermarks and no account required, for files up to 1 GB each. Convert one file or a hundred.
Is it safe to convert MP4 files here?
Safer than any upload-based converter. The conversion runs locally in your browser, so your MP4 files are never sent over the internet and never touch a server.
Will I lose quality converting MP4 to MKV?
No. This conversion preserves your content, and MKV output keeps everything the format supports.
Can I convert multiple MP4 files at once?
Yes. Free converts up to three MP4 files at a time. FormatFusion Pro batches without limits and downloads whole runs as a single ZIP.
Does it work on iPhone and Android?
Yes. FormatFusion runs in any modern mobile or desktop browser. No app install needed.