MKV to MP4 Converter
Processed locally in your browser — nothing is uploaded.
Quick answer
MKV (Matroska) is a flexible container that can hold many video, audio and subtitle tracks, but device and app support for it is poor. Converting to MP4 gives you a file that plays almost anywhere. When the MKV already holds H.264, this is a fast re-mux rather than a re-encode. It runs in your browser with ffmpeg.wasm — nothing is uploaded, and the engine downloads once (~32 MB).
How to mkv to mp4 converter
Add your MKV
Drag an .mkv file onto the drop zone or browse for it. The tool reads the container and the codecs of its tracks.
Convert to MP4
An H.264 (or H.265) video track is re-muxed into MP4; other codecs are re-encoded. The primary video and audio tracks are carried over.
Download the MP4
Save the .mp4 for broad playback on phones, TVs, editors and web uploads that will not open MKV.
Why does MKV play in VLC but nowhere else?
MKV is a superb container — open, flexible, able to bundle multiple audio languages, several subtitle tracks and chapters in one file. That flexibility is exactly why hardware support is thin. Phones, smart TVs, game consoles, most editors and nearly every web uploader never adopted it, so an MKV that plays perfectly in VLC on your PC is dead on arrival almost everywhere else. MP4 is the opposite: less flexible, but supported by essentially every device and app in existence. Converting trades features you probably are not using for compatibility you definitely need.
| Aspect | MKV (Matroska) | MP4 |
|---|---|---|
| Multiple audio tracks | Yes, many | Limited in practice |
| Multiple subtitle tracks | Yes (incl. image subs) | Limited (text subs) |
| Chapters | Yes | Basic |
| Device / TV support | Poor | Universal |
| Editor & upload support | Patchy | Excellent |
Is MKV to MP4 a re-encode or just a rewrap?
Most MKV files hold H.264 or H.265 video — codecs MP4 also supports — so the video stream can be copied straight into an MP4 container with no re-encoding. That is fast and completely lossless: the picture is byte-for-byte identical, only the wrapper changes. A full re-encode is only needed when the MKV uses a codec MP4 does not carry, or when audio has to be converted to AAC. Whenever it safely can, this tool takes the quick re-mux path.
How fast is it, and can it handle a big movie file?
A re-mux is quick even for a large file, since nothing is recompressed — but MKVs are often full-length movies, and that is where the honest caveat bites. The whole file is processed in browser memory, and the engine (ffmpeg.wasm) is single-threaded, slower than a desktop ffmpeg with all cores and a GPU. A multi-gigabyte movie may be too large for a browser tab and any re-encode of it will be slow. For big files, this is a case where a desktop tool may simply suit better; for short clips the browser is ideal. Compressing first can help.
Does my MKV get uploaded?
No. Everything runs locally in your browser and the file is never sent anywhere — which is also why there is no lengthy upload for a large movie. Check DevTools → Network to confirm: beyond the one-time engine fetch, no request carries your video. Your files stay on your machine.
Related video tools
Other conversions work the same way: MOV to MP4, AVI to MP4, or the universal video converter for any pair. If the MKV carried a subtitle track you want to keep, convert it in the subtitle converter and add it back to the MP4. You can also extract the audio as MP3.
Your files never leave your device
Processed locally in your browser — nothing is uploaded. You can verify it yourself: open your browser’s developer tools, watch the Network tab, and use the tool — no upload request is ever made.
Frequently asked questions
Why do not my devices play MKV files?
Phones, TVs, consoles and most editors never adopted the Matroska container, even though VLC on a PC handles it well. Converting to MP4 produces a file those devices support out of the box.
Is MKV to MP4 lossless?
When the MKV holds H.264 or H.265, yes — the video is copied into the MP4 container without re-encoding, so it is byte-for-byte identical. A re-encode only happens if the codec is one MP4 cannot carry.
Will all my audio and subtitle tracks be kept?
The primary video and audio are carried over. MP4 cannot hold everything MKV can, so extra audio languages and image-based subtitle tracks may not all transfer. Keep the MKV if you need every track.
Can I convert a full-length movie MKV in the browser?
Small and short files, easily. A multi-gigabyte movie is processed in browser memory and may be too large for the tab; a desktop tool can suit big files better. Compressing first helps.
How do I keep the subtitles from my MKV?
Text subtitle tracks can be extracted and converted in the subtitle converter, then added back to the MP4 with the add-subtitles tool as a soft track or burned in.
Does the conversion change video quality?
Not when it is a re-mux, since the picture is untouched. If a re-encode is required, the loss at a matching bitrate is not visible in ordinary viewing.
Is anything uploaded during conversion?
No. All processing is local to your browser. You can verify there is no upload in the Network tab of your developer tools.