Free MKV to MP4 Converter Usually a lossless remux
MKV is what Plex libraries, disc rips and fansubbed releases live in, and it is the one container Safari, QuickTime, an iPhone, most smart TVs and most editors refuse outright. The useful part is that an MKV normally already holds H.264 video and AAC audio, the exact pair MP4 wants, so the conversion is a remux. The streams are lifted into an MP4 box untouched, an episode sized file is through in seconds, and the picture is identical to the original. This page covers when that happens, when it does not, and what MKV carries that MP4 has no room for. The work runs inside this tab, so the file is never uploaded.
- Usually lossless
- Nothing uploaded
- 20 files at a time
Convert MKV to MP4
MP4, MOV, M4V, MKV, AVI, WMV, WebM, TS, MTS and more
Up to 20 clips at once
Privacy-first. No uploads. If this helps, share it.
- Your library stays your library
The conversion runs on a WebAssembly build of FFmpeg inside this page, reading the file straight off your disk. That matters more with MKV than with most formats, because MKV is where people keep disc rips, home recordings and whole seasons they would rather not copy onto somebody else's server.
- A remux, not a re-encode
When the MKV already holds codecs MP4 accepts, video and audio are copied across bit for bit instead of being encoded again. That is close to a plain file copy, so it takes a fraction of the time an encode would, and the result is pixel for pixel identical to what went in.
- A season at a time
Add up to 20 files per batch, 1 GB each. They are worked through in order rather than together, since the browser build has a single thread to use, and every finished file can be saved on its own or collected as a zip.
How to convert MKV to MP4
Add the MKV, leave the To dropdown on MP4, and the file is rebuilt as an MP4 in your browser. If it already carries streams MP4 accepts, which most MKVs do, they are copied straight across and the job is done in seconds with no quality loss. If something inside it cannot be copied, the file is re-encoded to H.264 with AAC audio instead, which runs at roughly real time on your own processor. Nothing is sent to a server either way.
- Add your MKV files
- Leave the To dropdown on MP4
- Download the MP4
MKV and MP4, side by side
Both are containers, boxes that hold video and audio streams rather than a way of compressing them. MKV is the more capable box: it will carry almost any codec, any number of audio languages, soft subtitles and chapters. MP4 is the stricter box, and that strictness is exactly why everything plays it. Converting is mostly a question of what fits through the door.
| What changes | MKV source | MP4 result |
|---|---|---|
| Container | Matroska, the .mkv extension | MP4, the .mp4 extension, the box every player and editor expects |
| Video codec | Usually H.264, sometimes H.265, VP9 or AV1 | Copied across untouched whenever the MP4 container accepts the stream, which covers H.264 and H.265, and also VP9 and AV1. Those last two are perfectly legal inside an MP4, they are simply much newer, so an MP4 built around them plays in fewer places than one built around H.264. |
| Audio codec | AAC, AC3, DTS, FLAC or Opus | Copied when MP4 accepts it, which covers AAC, AC3, DTS and Opus. A track that cannot be copied, FLAC being the usual one, sends the whole file down the re-encode path, so video and audio are both rebuilt as H.264 and AAC. |
| Extra tracks | Several audio languages, soft subtitles, chapters | The first video track and the first audio track. Subtitles and chapters do not come across |
| Where it plays | VLC, Plex, Kodi, most Android players | All of those, plus Safari, QuickTime, iPhone, iPad, smart TVs, editors and upload forms |
Size barely moves on a remux, because the same streams end up in a new box. A re-encode can land smaller or larger depending on what the source was, so size is not what this conversion is for. If the file is too big, run the MP4 through Compress Video afterwards.
Why convert at all, and what it costs you
Nothing about MKV is worse than MP4. It is the more capable container, which is why release groups and Plex users picked it in the first place. The problem is purely who accepts it. Apple does not support Matroska in QuickTime or Safari out of the box, plenty of TVs and set top boxes stop at MP4, and editor support is uneven in a way that depends on the codecs inside the file. Converting buys you that acceptance, and when the video stream moves across untouched it costs no quality to buy. What it does cost is everything MP4 has no room for: the second and third audio languages, the soft subtitle tracks and the chapter marks all stay behind in the original file.
The MKV on your disk is never modified. If the subtitle tracks or the second audio language matter to you, keep the MKV for watching at home and use the MP4 for the device or the app that would not take it.
Where the MP4 plays, and what still will not work
Most MKV files hold H.264 video and AAC audio, so most of the time that is what comes out, and that pairing is the one the widest range of things accept. It plays in Safari, QuickTime, the iOS Photos app, Chrome, Firefox, Windows Media Player, VLC, on Android, on smart TVs and on games consoles, and it imports into Premiere, Final Cut, DaVinci Resolve, iMovie and CapCut. It also gets past the upload forms that check the extension before they check anything else. What comes out of a remux is whatever went in, though, so a source built on a newer codec keeps that codec.
Burned in subtitles stay visible, because they are part of the picture. Soft subtitle tracks are a separate stream and do not survive the move, so keep the .srt file or keep the MKV.
There is no track picker here. Whichever audio track sits first in the MKV is the one that ends up in the MP4, and the rest are left behind with the subtitles and the chapters.
Some files will not open at all. DRM protected video cannot be decoded, so a purchased or rented file fails rather than converts, and a rip with a damaged header usually needs repairing before any converter can read it.
Convert an MKV in three steps
Nothing leaves this tab.
Add your MKV files
Drag them in or pick them from your device. A batch takes 20 files at 1 GB each, enough for most episodes, rips and recordings without having to split anything first.
Check the To dropdown
It is already on MP4. If what you actually want is the soundtrack on its own, switch it to MP3 without leaving the page and you get a 128 kbps, 44.1 kHz audio file instead.
Download the result
Save each file as it finishes, or take the whole batch as a zip. Your original MKV is untouched and still sitting where it was.
What people run into with MKV
MKV problems are rarely about quality. They are about an app somewhere in the chain that will not open the file, and about the workarounds people try before converting.
Renaming the extension does not work
Changing film.mkv to film.mp4 changes the label on the box and nothing inside it. The player opens the file, reads a Matroska header where it expected an MP4 one, and gives up. A real conversion rewrites the container structure, which is why it takes a few seconds rather than none.
Editor support depends on the codecs inside
Editor support for MKV is uneven, and what decides it is usually the codecs inside the file rather than the container. Premiere Pro does import MKV, though in practice that means the common combinations like H.264 video with AAC audio, and files carrying HEVC video or Opus audio are often refused. DaVinci Resolve opens many MKV files, again depending on what is inside. Final Cut Pro and iMovie do not list MKV among the formats they accept, so those normally want a converted file. Remuxing to MP4 takes the guesswork out, and since the video stream is unchanged you are editing the same frames you started with.
Apple devices are the usual wall
Safari will not play an MKV, QuickTime will not open one, and an MKV copied to an iPhone or iPad sits there as a file the Photos app does not recognise. This is the most common reason people end up converting, and a remux clears it without touching the picture.
Desktop tools are heavier than the job
Handbrake and its relatives are excellent, and they are also an install, a preset menu and, on their default settings, a full re-encode of a file that did not need one. For a straight container swap, a browser tab is enough.
An MKV is usually somebody's whole library
The MKV files people convert are disc rips, Plex media, camera archives, recorded streams and old family video someone digitised years ago. They are also big, often near the 1 GB per file limit here. Handing a file that size to an upload based converter means a long wait going up, a place in a queue and a long wait coming back down, for work that is frequently over in seconds.
None of that applies here. FFmpeg runs in the page itself, reads the file from your disk and writes the MP4 back to your downloads folder. Close the tab and there is nothing left to delete, on your side or ours, and there is no sign in that could build up a record of what you converted.
What that means in practice
- The MKV never leaves your own machine
- We never receive the file, or even its name
- No account, no watermark, no upload wait
- A re-encode uses your own processor, so a long film takes a long time
MKV to MP4 troubleshooting
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Drag the MKV onto the converter above, keep the To dropdown on MP4, and save the file once it finishes. Nothing to sign up for, nothing uploaded, and nothing stamped on the result.
Reviewed in August 2026 for browser based MKV conversion.