MP4 to MKV Converter

Repack an MP4 into a flexible MKV for media servers, subtitles, and multiple audio tracks. Free, in your browser, with no signup and no watermark.

Select MP4 file →

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Updated August 2026

MKV is an open container that can hold many audio tracks, soft subtitles, and chapters in a single file, which makes it the favorite for Plex, Kodi, and home media libraries. Converting your MP4 to MKV puts the same video into that more flexible container, free and right in your browser with no signup. When the codecs already fit, the change is lossless.

Free, no sign-upNo account, no trial

Runs in your browserNothing to install

Works on every devicePhone, tablet, laptop

No watermarkClean output, every time

How it works

How to convert MP4 to MKV

1
Upload your MP4
Drag your MP4 onto the converter or pick it from your device. Nothing to install.
2
Choose MKV and convert
Select MKV as the output and start. Free, with no sign-up and no watermark.
3
Download your MKV
Save the finished MKV, or open it in the editor to trim, crop, or resize it first.

Try it

Estimate your MKV

Pick a video bitrate and a length to see the MKV file size before you convert.

Video bitrate

Length5 min

1 min30 min

Estimated MKV size183MBSharp 1080p

An estimate. Real size varies with resolution, frame rate, and how much the picture moves.

The formats

MP4 vs MKV

MP4

MPEG-4 Part 14

The video format that plays everywhere

Type: Video container
Holds: H.264 video plus AAC audio, sometimes subtitles
Typical size: Large, it carries video
Plays on: Phones, browsers, TVs, almost any player

Best for:Watching and sharing video

MKV

Matroska Video

An open container that holds almost anything

Type: Open video container
Holds: Almost any codec, plus several audio and subtitle tracks
Typical size: Large, depends on the codec inside
Plays on: VLC and most modern players, less on default phone apps

Best for:Movies with multiple audio tracks and subtitles

Will it lose quality?

When the codecs already match MKV, the converter can change the container without re-encoding, so the picture stays identical.
When the video has to be re-encoded for MKV, a high bitrate keeps it visually close to the MP4.
Converting cannot add detail the MP4 never had. The output is at best as good as the source.

Use cases

What people use it for

Play anywhereMake a clip your device supports

Video editorsGet footage your software accepts

Web videoUse a format browsers play

CourseworkHand in a standard video file

SharingSend a clip people can open

Troubleshooting

If something looks off

The MKV will not play

Some players are picky about codecs. Try it in VLC, which opens almost anything, or convert again and let the converter re-encode the video.

The file got larger

A format change can shift the size, and re-encoding at a high bitrate adds overhead. Lower the bitrate or trim the clip for a smaller file.

Audio and video drift out of sync

Re-download the source and convert again. If a long recording drifts, splitting it into shorter pieces usually fixes the sync.

FAQ

MP4 to MKV questions

Is the MP4 to MKV converter free?

Yes. EchoWave converts MP4 to MKV with no signup, no file-count limit, no trial, and no watermark. Upload your video, convert it, and download the MKV from your browser.

How do I convert MP4 to MKV?

Upload your MP4, choose MKV as the output, and start. When it finishes, download the MKV or open it in the editor to trim, crop, or adjust the clip first.

Is converting MP4 to MKV lossless?

It can be. MKV accepts the same H.264 and AAC streams an MP4 uses, so when the codecs already fit the converter can change the container without re-encoding and the picture stays identical. If a re-encode is needed, a high bitrate keeps it close to the source.

Why convert MP4 to MKV?

MKV holds multiple audio tracks, soft subtitles, and chapter markers that MP4 handles less flexibly, which is why media servers like Plex and Kodi prefer it. It is also a tidy container for archiving a movie with all its extras in one file.

Does MKV reduce the file size?

Not on its own. MKV is a container, not a compression method, so the file size mostly tracks the video and audio inside. A straight container change keeps the size close to the original MP4.

After converting MP4 to MKV, what plays the file?

VLC, Plex, Kodi, and most modern media players open MKV easily. Phone gallery apps and some TVs are pickier, so if a device refuses it, convert back to MP4 for the widest playback.

Can I keep subtitles and multiple audio tracks?

MKV is built to carry several audio tracks, soft subtitles, and chapters in one file, which is its main advantage over MP4. The tracks present in your source are kept in the MKV container.

Does the MP4 to MKV converter work on Mac, Windows, iPhone, and Android?

Yes. Repacking an MP4 into an MKV happens in a browser tab on Windows, macOS, a Chromebook, Linux, an iPhone, an iPad, or Android, with nothing to install. The MKV you download is aimed at media servers and desktop players like Plex, Kodi, and VLC, so that is where it will feel most at home rather than a phone gallery app.

What is the difference between MP4 and MKV?

Both are containers, so they can hold exactly the same H.264 or H.265 video and AAC audio. The difference is what else they carry: MKV holds several audio tracks, switchable soft subtitles, and chapters comfortably, while MP4 handles those less flexibly. MP4 wins on compatibility, MKV wins on flexibility.

Is MKV better quality than MP4?

Neither container improves or degrades quality on its own, because the picture comes from the codec inside. Moving an MP4 into an MKV without re-encoding leaves the video identical. What MKV adds is room for lossless audio tracks and extras that MP4 would have to leave behind.

How long does it take to convert MP4 to MKV?

When the codecs already fit, the conversion is a repack rather than a re-encode, so it finishes far faster than a normal format conversion and is often over in moments. A re-encode, where one is needed, takes longer and tracks the length of the video.

Is there a file size limit for MP4 to MKV conversion?

There is no file-count limit, and multi-gigabyte sources are normal for MKV since it is the container people archive full-length films in. The work runs on our servers rather than on your machine, so a large MP4 does not depend on how powerful your laptop or phone is.

When to use MKV instead of MP4

MP4 is the container that plays everywhere. MKV is the container that carries everything. That single difference decides which one you want.

MKV is the right choice when one file has to hold more than one thing:

Several audio tracks. An original language plus a dub, or a commentary track sitting alongside the film. MP4 can technically hold extra tracks, but players treat them inconsistently and plenty of tools quietly drop them.
Soft subtitles. MKV stores subtitles as text you can switch on, off, or swap between languages, rather than burning them permanently into the picture. Plex, Kodi, and VLC all surface them as a menu.
Chapters and metadata. Chapter markers, track names, and cover art survive in MKV, which is what makes it the format of choice for archiving a film with all its extras in one tidy file.
Media servers. Plex, Jellyfin, and Kodi libraries are built around MKV, so a converted file slots straight in with its tracks intact.

MP4 remains the better container when the destination is a phone gallery, a social upload, or a web page, since some TVs and mobile apps still refuse MKV. If that is where your file is heading, convert the other way with MKV to MP4 instead.

MP4 to MKV without quality loss

Because MKV is a container and not a compression format, this conversion can be a straight repack. The same H.264 or H.265 video stream and AAC audio are lifted out of the MP4 and written into an MKV untouched, so there is no re-encode, no generation loss, and the picture that comes out is exactly the picture that went in. File size stays close to the original for the same reason.

That fast path applies whenever the codecs already inside your MP4 fit MKV, which covers the overwhelming majority of MP4 files in the wild. Where a re-encode genuinely cannot be avoided, a high bitrate keeps the result visually indistinguishable from the source.

Two things the conversion will not do, both of which people reasonably expect it might. It will not shrink your file, because moving the same data into a different wrapper saves nothing: use the video compressor for that. And it will not improve the source, since MKV can carry a better file than MP4 can but cannot restore detail that was thrown away before it arrived.

What people say after converting with EchoWave

About the EchoWave team

EchoWave is a browser-based video and audio editor built by Lemon Vault LLC since 2018. The people who build the editor write these guides and test every step in the production app before publishing.

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