Converters MKV to MP4 converter
Convert Matroska MKV files to MP4 in seconds, copying the video across rather than re-encoding it.
Anything but Original forces a re-encode.
Quality, if a re-encode is needed
Drag files here, or
Converted to MP4 on your device. The converter itself is a 9.8 MB download, once.
Ready. Runs locally on your device.
Your files stay on your device. The tool works directly in your browser, using your device to process your files. Nothing is sent to our servers, and we never receive, store, or see your files or figures.
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Cite this page
Reembun. (2026, August 12). MKV to MP4 converter. https://reembun.com/mkv-to-mp4
How to use it
Add the MKV
Drop it in or choose it. Large files are fine, because nothing is uploaded and there is no size limit to hit.
Wait for the engine once
The converter downloads on the first run, then stays cached.
Convert
MP4 is already the target. Where the streams inside are already compatible they are copied rather than re-encoded, which is fast and loses no quality.
Download the MP4
The result reports whether the streams were copied or re-encoded, so you know which of the two just happened.
MKV holds anything, which is both its strength and its problem
Matroska was designed to be a container that could carry anything: any video codec, any audio codec, unlimited subtitle tracks, chapters, attachments, several audio languages side by side. It succeeded completely at that, and it is why MKV is the format of choice for archiving and for anything that needs to keep more than a single picture and a single soundtrack.
The price is support. MKV never became a consumer standard, so smart TVs, phones, consoles, Premiere, and a good deal of upload software will not open it. The video inside is usually ordinary H.264 those same devices decode every day. The wrapper is the obstacle.
The conversion is a rewrap, not a re-encode
Because MP4 will happily carry H.264 and HEVC, and most MKV files contain one of the two, this conversion copies the video stream straight across. Nothing is decoded, nothing is compressed again, and the picture in the MP4 is the same data that was in the MKV.
Where it falls back to a real re-encode:
| Video inside the MKV | What happens |
|---|---|
| H.264 (x264) | Copied. Seconds, no quality loss. |
| HEVC / H.265 | Copied. Seconds, no quality loss. |
| VP9 or AV1 | Re-encoded to H.264. Slow, some quality lost. |
| MPEG-2 or Xvid | Copied where legal, otherwise re-encoded. |
The audio follows the same rule. AAC and MP3 are copied; Opus, Vorbis and FLAC are re-encoded to AAC, because MP4 cannot carry them.
What you lose, and it is worth knowing beforehand
MKV is the richer container, so a conversion to MP4 is a narrowing. Specifically:
- Subtitle tracks are dropped. MP4’s subtitle support is limited and does not represent SSA/ASS styling.
- Only the first audio track survives. A file with English and Japanese tracks keeps whichever comes first.
- Chapters may not survive, depending on how they were written.
- Attachments such as embedded fonts have no MP4 equivalent at all.
If any of that matters to you, the honest answer is to keep the MKV and play it with VLC or mpv, both of which open it without complaint on every platform.
Nothing is uploaded, and there is no size limit
MKV files are frequently several gigabytes, which is exactly the size that upload-based converters either reject outright or put behind a paid tier. There is no upload here. The file is read from your disk and the result written back to it, so the only limit is what your own machine can hold in memory, roughly 2 GB on a desktop browser.
Common questions
Does converting MKV to MP4 lose quality?
Not when the video inside is H.264 or HEVC, which covers the overwhelming majority of MKV files. Those are copied into the MP4 without being decoded, so the picture is bit-for-bit identical. Quality is only lost when the MKV holds VP9 or AV1, which MP4 handles poorly or not at all, and the video has to be re-encoded.
What happens to my subtitles?
They are dropped. MKV can carry several subtitle tracks in formats such as SSA and ASS with full styling; MP4 supports only a narrow subset and handles it badly. If subtitles matter, keep the MKV, or extract them separately before converting.
What about multiple audio tracks?
Only the first is kept. MKV files from a release with several language tracks will come out with whichever one is listed first. There is no way around that in a browser-based tool short of a full track editor.
Why is my MKV file not playing on my TV?
MKV is an open container that never became a consumer standard, so smart TVs, games consoles, older media players and most phones do not support it. The video inside is usually ordinary H.264 that the same device would play happily in an MP4. The container is what it refuses.
How long does a 4 GB MKV take?
A minute or two, most of it spent reading and writing the file rather than converting it. Because nothing is re-encoded, the size of the file matters far more than its length or resolution.
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