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How to Convert MKV to MP4 (and When You Don't Need to Re-Encode)

October 8, 2026

Short answer: upload the MKV to Ident Convert, choose MP4 and download it. For a small clip that takes a minute. For a full movie, use a desktop tool instead, because our online limit is 150 MB. Both ways are explained below, along with the one thing most guides skip: whether you need to re-encode the video at all.

Convert MKV to MP4

Why MKV won't play

MKV and MP4 are containers: boxes that hold a video track, one or more audio tracks and sometimes subtitles. The picture quality does not come from the box, it comes from the codec inside it, such as H.264 or H.265. Adobe's comparison makes the same point: the same encoded video looks identical in either container.

The difference is who can open the box:

  • MP4 plays on almost every phone, TV, game console, browser and editing program.
  • MKV is flexible (many audio languages, rich subtitles, chapters), and desktop players like VLC handle it well, but phones, smart TVs and web uploads often do not.

That is why a movie that plays on your PC may refuse to open on an iPhone or in a video upload form.

Do I need to convert, or just re-pack?

There are two different jobs here, and they are easy to mix up:

  • Remux means moving the same video and audio into a new MP4 box without touching them. It is almost instant and loses nothing. It works when the codecs inside the MKV are ones MP4 accepts (typically H.264 or H.265 video with AAC or AC3 audio).
  • Re-encode means decoding and compressing the video again. It works for any MKV but takes longer and is slightly lossy.

Ident Convert re-encodes: the output is H.264 video with AAC audio at a standard quality setting, so it plays almost everywhere. Because of that it is slightly lossy, and it is the right choice when you are not sure what is inside the MKV or when the file uses a codec MP4 does not support.

How to convert MKV to MP4 online

  1. Open the Ident Convert converter and upload your MKV.
  2. Choose MP4 as the output.
  3. Wait for the conversion and download the file.

This is what to know before you start:

  • Size and time. Files up to 150 MB are accepted. Long or high-resolution videos can take several minutes, and a conversion that runs past about 4 minutes is stopped with a message.
  • One video track and one audio track are kept. Extra audio languages and subtitles are not carried over.
  • 5.1 surround sound is kept.
  • HDR and 10-bit video is converted to normal SDR colors and 8-bit, so it plays on any screen.

The page for this pair has the same details: MKV to MP4. If you only want the sound, there is also MKV to MP3.

For big files: a free desktop route

A two-hour movie is far larger than 150 MB, so an online tool is the wrong place for it. Two free options:

HandBrake (graphical, runs on Windows, Mac and Linux): open the MKV, choose an MP4 preset, press Start. It re-encodes, so it is slower, but it lets you keep subtitles and extra audio tracks.

FFmpeg (command line) can remux in seconds when the codecs allow it:

ffmpeg -i movie.mkv -c copy movie.mp4

-c copy means "do not re-encode". If it fails with a message about a codec or a subtitle format, the MKV contains something MP4 cannot hold, and you need a real re-encode instead (HandBrake, or the same command without -c copy).

MKV or MP4: which should you keep?

  • Keep MKV for your own archive of movies with several languages and styled subtitles, played on a computer.
  • Use MP4 for anything you share, upload, play on a phone or TV, or edit.

Frequently asked questions

Does converting MKV to MP4 lose quality?

Remuxing loses nothing. Re-encoding, which is what Ident Convert does, is slightly lossy, but at the standard quality setting the difference is hard to see on normal footage.

Will my subtitles survive?

Not in Ident Convert: subtitles and extra audio tracks are dropped. For a file where you need them, use HandBrake or FFmpeg.

Why is my MP4 smaller or larger than the MKV?

The file size depends on the codec and quality settings, not the container. A re-encode can shrink some files and enlarge others.

Are my videos kept after converting?

No. Files are processed for the conversion and removed afterward. The Privacy Policy has the exact details.

Related guides

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