Click to choose an MKV or drop it here
MKV in, MP4 out — converted in your browser, never uploaded. Other video types work too.Video and audio are processed in your browser by FFmpeg (ffmpeg.wasm), free software under the GPL-2.0-or-later and MIT licenses — licenses & source.
About converting MKV to MP4
To convert MKV to MP4, drop your .mkv file on the box above and press Convert to MP4. Most MKV files hold H.264 video, so the tool simply repacks them into an MP4 in a few seconds, with no quality loss.
MKV and MP4 are both containers: a box that holds the picture, the sound and the subtitles. The picture inside an MKV is often already fine for an MP4. Only the box is wrong for your iPhone, your Mac or your editor. So this tool changes the box first and only re-encodes when it really must.
Everything runs in your browser. Your video is never uploaded.
Features
- Fast repack — H.264 or HEVC video is moved into the MP4 untouched, in seconds
- No quality loss on a repack — the picture is bit-for-bit the original
- Sound fixed for you — AC3, DTS, Opus or FLAC sound is turned into AAC, while the picture stays untouched
- Subtitles kept — text subtitles (SRT, ASS) from the MKV become MP4 subtitles you can turn on
- Honest result — the page tells you if it repacked or re-encoded
- Optional resize — 1080p, 720p or 480p, if you also want a smaller file
- Private — no upload, no sign-up, no watermark
What is an MKV file?
MKV stands for Matroska Video. It is a free, open container from 2002. It can hold almost anything: many sound tracks (for example English and Spanish), many subtitle tracks, chapters, and nearly every video codec.
That is why MKV is popular for movies, TV recordings, screen recordings (OBS saves MKV by default) and downloads. But that freedom has a cost: many devices do not open MKV at all, even when the video inside is ordinary H.264.
Why MP4 plays everywhere
MP4 is the standard video file of phones, cameras and the web. Apple, Android, Windows, smart TVs, browsers, editors and social apps all play it. If you send an MP4 to someone, it will open.
| Where you play it | MKV | MP4 |
|---|---|---|
| iPhone and iPad (Photos, Files) | No | Yes |
| Mac (QuickTime, Photos) | No | Yes |
| Android phone | Often, depends on the app | Yes |
| Windows 10 and 11 (Media Player, Films & TV) | Yes | Yes |
| Smart TV from a USB stick | Many, not all | Yes |
| Web browser on a web page | No | Yes |
| iMovie and many video editors | Often not | Yes |
| WhatsApp, Instagram, Facebook | No | Yes |
| VLC (any computer) | Yes | Yes |
If the video should play on an Apple device, go into an editor, or be shared online, MP4 is the safe choice.
How fast is it?
It depends on what is inside the MKV. The page checks the file first and picks the fastest way that still gives a file that plays everywhere:
- H.264 or HEVC video with AAC or MP3 sound — the most common MKV. It is repacked: a few seconds, even for a full movie, and nothing is lost.
- H.264 or HEVC video with AC3, DTS, Opus or FLAC sound — the picture is repacked untouched, and only the sound is turned into AAC. Usually well under a minute.
- Other video (VP9, MPEG-2, Xvid, AV1) — the picture must be re-encoded to H.264. This runs in your browser on one processor core, so it is slow: often about as long as the video itself, or longer, and slower on a phone. A 5-minute clip may take 5–15 minutes on a laptop.
Changing the resolution always means re-encoding, so leave it on *Keep the original* if you only want a fast MP4.
Subtitles and sound tracks
- Text subtitles (SRT, ASS, SSA) are kept as MP4 subtitles. Turn them on in your player. Fancy ASS styles (colours, positions) become plain text.
- Picture subtitles (PGS from Blu-ray, VobSub from DVD) cannot go into an MP4, so they are left out. The page tells you.
- Only the first sound track and the first subtitle track are kept. An MP4 with many tracks is poorly supported anyway.
- To burn subtitles into the picture, so they always show, use Add Subtitles to Video.
How to use it
- Click the box and choose your MKV, or drag it onto the box
- Leave the repack option ticked — it makes the conversion take seconds when it can
- Leave Resolution on *Keep the original* unless you also want a smaller file
- Press Convert to MP4 and read the message: it says if it repacked or re-encoded
- Play the result, then press Download MP4
Frequently asked questions
How do I convert MKV to MP4 without losing quality?
Use the repack. If the MKV holds H.264 or HEVC video (most do), this tool moves the video into an MP4 without re-encoding, so the picture is exactly the same. Keep the repack option ticked and the resolution on *Keep the original*.
Why is my MKV converting slowly?
The video inside is not H.264 or HEVC — often VP9, MPEG-2 or Xvid — so it has to be re-encoded, and that runs on your own computer. The page says *Re-encoding* when this happens. A shorter clip, or 720p, is faster.
Are subtitles kept?
Text subtitles (SRT, ASS) are kept as MP4 subtitles that you can turn on in your player. Picture subtitles from Blu-ray or DVD cannot go into an MP4 and are left out.
Can I play an MKV on an iPhone?
Not in the Photos or Files app. Convert it to MP4 here first; most MKV files are repacked in seconds and then play on the iPhone, iPad and Mac.
Is there a file size limit?
There is no upload, so there is no upload limit. The limit is your browser's memory: files up to about 1–2 GB usually work on a computer. Phones handle less.
Is my video uploaded?
No. The converter (ffmpeg) runs inside your browser, on your device. The video never leaves it.
Related tools
- AVI to MP4 — the same job for old AVI videos
- Video Converter — convert to MP4, WebM or MKV from many formats
- MOV to MP4 — for iPhone and QuickTime videos
- Compress Video to Size — make the MP4 fit a size limit
- Add Subtitles to Video — burn subtitles into the picture
- MP4 to MP3 — keep only the sound
Credits
Conversion is powered by ffmpeg.wasm (FFmpeg and x264, licensed under GPL-2.0).
