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Guide

MKV to MP4: convert it free in your browser

Drop an MKV file in the box above and get an MP4 that plays on phones, TVs and social apps. The file stays on your device.

In short

  • This converter turns an MKV file into an MP4 that plays almost anywhere.
  • Most files are done in seconds, because H.264 video is copied as it is.
  • Copied video loses no quality. Other video is re-encoded once at a high setting.
  • Nothing is uploaded. The whole conversion runs inside this browser tab.
  • It is free, with no account and no watermark.
Drawn desk scene: a phone and a laptop with a lime arrow between them.
Illustration by Cutroom, AI-generated

MKV to MP4

Runs in your browser · files never leave this page

Drop a MKV file here

or

The engine reads the file first. An H.264 picture with AAC sound is copied into the MP4 with no re-encode. Anything else is written as H.264 + AAC.

Choose a file first.

Your file never leaves this page. The engine downloads once, the work happens in this tab, and there is no upload, no account and no storage. Close the tab and the file is gone unless you downloaded it.

More free tools: Video compressor · Video resizer · Video to MP4 · Video to MP3 · Video clipper · all tools

Try for freeCutroom turns one take into a finished 9:16 video with captions, b-roll and a hook. Your first video is free.

What is an MKV file?

MKV (Matroska) is a box that can hold almost any video, sound and subtitles.

  • MKV files come from screen recorders, downloads and video rips.
  • iPhones, many editors and social apps will not open an MKV file.
  • Moving the same video into an MP4 fixes that. Often nothing else changes.

What the converter does

It copies what an MP4 can hold as it is, and re-encodes only what it cannot.

  • Copied: H.264 video and AAC sound go into the MP4 untouched. No quality loss.
  • Re-encoded: any other video becomes H.264 at a high quality setting (CRF 23).
  • Sound: any other sound becomes AAC at 160 kbps.
  • Web ready: the MP4 is set up to start playing before it fully loads.

What happens to each part of your MKV file

The first video track and the first sound track are used. The rest is left out.

Inside the fileWhat you get in the MP4How long
H.264 videoCopied as is, no quality lossSeconds
HEVC or VP9 videoRe-encoded once to H.264Minutes for a long file
AAC soundCopied as isSeconds
AC-3, DTS, FLAC or Opus soundConverted to AAC at 160 kbpsSeconds
Subtitle tracksLeft out-
Extra sound tracks (other languages)Only the first one is kept-

  • Inside the file: H.264 video

    What you get in the MP4
    Copied as is, no quality loss
    How long
    Seconds

  • Inside the file: HEVC or VP9 video

    What you get in the MP4
    Re-encoded once to H.264
    How long
    Minutes for a long file

  • Inside the file: AAC sound

    What you get in the MP4
    Copied as is
    How long
    Seconds

  • Inside the file: AC-3, DTS, FLAC or Opus sound

    What you get in the MP4
    Converted to AAC at 160 kbps
    How long
    Seconds

  • Inside the file: Subtitle tracks

    What you get in the MP4
    Left out
    How long
    -

  • Inside the file: Extra sound tracks (other languages)

    What you get in the MP4
    Only the first one is kept
    How long
    -

This is the whole editor

Highlight a phrase and a clip lands on those exact words. No timeline, no keyframes, no layers.

CLIPS · 5I have thisexact conversationeverysingle week. Somebody sits down and says,oh yeah, I takecinnamonevery day.And honestly, doc, I have no idea if it works.So let me tell you what isin that capsule.a clip lands on these wordscut from the editTAKING CINNAMONEVERY DAY?is it doing anythingHeadlineMusicCaptionsTHIS VIDEOLength25.0sClips5Words removed18Export video

How to convert MKV to MP4

Four steps, all in this tab.

MKV to MP4 in four steps

  1. Drop your MKV file

    In the box at the top

  2. The engine reads it

    Which video and sound it holds

  3. Copy or re-encode

    Only what MP4 cannot hold is redone

  4. Download the MP4

    Saved to your device

Limits of a browser tool

Everything runs on your own device, so your device sets the limits.

  • File size: up to 500 MB runs comfortably. Bigger files may run out of memory.
  • Speed: the engine uses one processor core, so a long re-encode takes minutes.
  • First run: the engine downloads once, about 32 MB. After that it starts fast.
  • Phones: it works, but a laptop is faster and has more memory.

Questions people ask

Does converting MKV to MP4 lose quality?
Not when the video is H.264: it is copied bit for bit. Other video is re-encoded once at a high quality setting (CRF 23), which is hard to tell apart from the original.
Why are my subtitles gone after converting?
The converter keeps the first video track and the first sound track only. Subtitle tracks are left out. Subtitles drawn on the picture itself stay, because they are part of the video.
How long does MKV to MP4 take?
Seconds when the video is H.264, because it is only copied. HEVC or VP9 video is re-encoded on one core of your device, so a long file can take many minutes.
Can I convert MKV to MP4 on my phone?
Yes, in the phone's browser. A phone has less memory than a laptop, so large MKV files are safer on a computer.
Is my MKV file uploaded anywhere?
No. The tool runs inside this browser tab, so your MKV file never leaves your device. Only the engine itself is downloaded, about 32 MB, once per visit.

Want a finished video with captions, not just a converted file? Cutroom edits your clip for you. Your first video is free.

Try for freeYour first video is free, no card, and you have 7 days to make it. It carries a Cutroom mark; Lite at $19.99/month removes it