MP4 to MKV Converter

Repackage an MP4 as an MKV for media servers, players, and archives that prefer Matroska.

100% free
No signup needed
Browser-based

Why use Jupitrr's MP4 to MKV converter?

No re-encoding

MKV can hold the same codecs as MP4, so the streams are copied across and the picture is untouched.

Never uploaded

Your MP4 file is converted inside your browser and never leaves your device.

Free, no watermark

No signup, no install, and nothing added to your file.

How it works

Choose a MP4 file

Drop a MP4 video up to 1 GB onto the converter, or pick it from your device.

Keep MKV selected

MKV is already selected. You can switch to another output format if you need one.

Convert and download

The video is converted in your browser. Preview the MKV file, then download it.

What is a MP4 to MKV converter?

Same video, more flexible container.

MKV (Matroska) is an open container that can hold almost any video and audio codec. Media servers such as Plex and Jellyfin, players such as VLC, and many archive workflows use it as their standard format.

Because MKV accepts the H.264, HEVC, and AAC streams inside an MP4, converting MP4 to MKV only rewrites the container. It finishes in seconds and keeps the original quality.

When to reach for it

Media server libraries

Keep a Plex or Jellyfin library in one consistent format.

Archiving

Store recordings in an open, well-documented container.

Tools that expect MKV

Feed scripts and apps that only look for .mkv files.

Matching recordings

Line up phone clips with OBS recordings that are already MKV.

Frequently asked questions

Does MP4 to MKV lose quality?

No. The video and audio are copied into the MKV container without re-encoding, so the quality is identical.

Will the MKV play on my iPhone or in QuickTime?

No. Apple devices and QuickTime do not open MKV files. Keep the MP4 for Apple devices, or use VLC or Infuse to play the MKV.

Can I add subtitles or extra audio tracks?

Not with this converter. It copies the main video track and the first audio track. Use MKVToolNix to add subtitle or language tracks afterwards.

Is my MP4 file uploaded to a server?

No. The MP4 file is read and converted by your browser on your device. It is never sent to Jupitrr, and closing or refreshing the tab clears the working files.

Is there a file size limit?

Files up to 1 GB can be converted. Larger files can run out of browser memory, so trim or compress very long recordings first.

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