Convert MKV to MP4
Your files are processed on your device. We never upload them.
Video is read and written with Mediabunny, under the Mozilla Public License. Browsers without their own AAC encoder use FFmpeg's, under the GNU LGPL.
How to convert MKV to MP4
- 01A ▸Choose your MKV videos, or drop them on the page.
- 02A ▸Keep Copy for the fastest result, or pick Re-encode to H.264 for an old player.
- 03A ▸Select Convert to MP4, then download each video.
About MKV to MP4
Where MKV files come from
MKV (Matroska) is a flexible container used by screen recorders such as OBS, by video downloads, and for films with several sound tracks and subtitles. iPhones, many TVs, video editors, and upload forms don't open MKV, but they open MP4.
What changes
- H.264 or HEVC video and AAC or MP3 sound are copied as they are, so quality, size, and frame rate don't change.
- VP8, VP9, or AV1 video is re-encoded to H.264, because MP4 players expect it. This takes a good fraction of the video's length on a computer, and longer on a phone.
- Only the main picture and sound are kept. Other sound tracks, subtitles, chapters, and attached fonts are left out.
- Surround sound in AC-3 or E-AC-3 is kept as it is; Chrome and Firefox don't play it, while VLC, TVs, and Apple's apps do.
Measured
Our one-minute 1080p sample at 30 frames a second with H.264 video and AAC sound in MKV (a synthetic test pattern, which is easier to encode than real footage), converted in Chrome on a laptop. Phone timings are still to be measured.
| MKV file | 61.1 MB |
|---|---|
| MP4 file | 61.3 MB |
| Time (Chrome, laptop) | 0.3 seconds, nothing re-encoded |
| Time on phones | still to be measured |
In your browser
Copying works in every current browser, because it needs no decoder. Re-encoding VP9 or AV1 uses the browser's own decoders and encoders (WebCodecs), found in Chrome, Edge, and Firefox, and in Safari 16.4 and later. Opus or Vorbis sound needs WebCodecs audio, which Safari has from version 26.
Limits
- DTS and Dolby TrueHD sound can't be converted here yet, so those files stop with a message. The free apps VLC and HandBrake convert them on a computer.
- Subtitles in MKV files are left out rather than turned into MP4 subtitles.
Other options
- Extract audio: keep only the sound, as M4A, MP3, or WAV.
- Merge videos: join several recordings into one.
- Video converter: convert to WebM or MOV instead.
Questions
Does converting MKV to MP4 lose quality?
Not with Copy, the default. When the MKV holds H.264 or HEVC video and AAC or MP3 sound, as most do, they are copied into the MP4 exactly as they are. Only tracks MP4 players can't handle are re-encoded.
Are my videos uploaded?
No. Your files are processed on your device. We never upload them.
What happens to subtitles and extra sound tracks?
The main picture and the main sound track are kept. Extra sound tracks (other languages, commentary) and subtitles are left out, and the result says so.
Why does my MP4 have no sound in Chrome?
The MKV's sound is probably surround sound in AC-3 (Dolby Digital) or similar. It is kept as it is, and plays in VLC, on TVs, and in Apple's apps, but not in Chrome or Firefox. Converting that sound isn't available here yet.
Is there a file size limit?
No daily limit and no watermark. Files over 100 MB show a warning first because they can be slow on phones, and you can go ahead anyway. The video is read and written in pieces, so a long film doesn't need to fit in memory.