MP4 to MKV Converter – Free Online

Video & Audio Converter

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How to Convert MP4 to MKV Online

Upload your MP4 file

Drag and drop your .mp4 file onto the page or click to browse. You can select several MP4 files at once to batch-convert them.

MKV is preselected

The output format is already set to MKV, so you can convert immediately. If you need to, adjust the codec, resolution, frame rate or bitrate in the settings panel first.

Convert and download

Click Convert. The MKV file is processed on your own device; nothing is uploaded to a server. When it finishes, click Download to save it (or Download all to get a batch as a ZIP).

Why Convert MP4 to MKV?

MKV can hold anything MP4 can and more: unlimited audio and subtitle tracks, chapters, attachments and any codec. Converting MP4 to MKV is the usual first step when building a media-server library in Plex, Jellyfin or Kodi where you want every language and subtitle in one file.

The video is re-encoded into the Matroska container with the source codec and bitrate kept by default, so quality is preserved visually; a full-length film takes a few minutes depending on its resolution.

Private by design: your MP4 file is converted on your own device and never uploaded.
MKV preselected: the output format is already chosen, so it is a one-click conversion.
Batch friendly: convert several MP4 files in one go and download them as a ZIP.
No limits, no watermark: free for files of any size, with nothing stamped on the output.

MP4 vs MKV

MP4 (MPEG-4 Part 14): MP4 is the most widely supported video container in the world. It usually carries H.264 or H.265 video with AAC audio, plays on every phone, browser, TV and editing app, and is the safest choice for sharing. It is best for sharing, social media, web playback and mobile devices.

MKV (Matroska Video): MKV (Matroska) is an open container that can hold practically any codec plus multiple audio tracks, subtitle tracks and chapters, which makes it popular for archiving films and TV episodes. It is best for archiving, multi-language releases and media servers.

In short: keep MP4 when the priority is sharing, social media, web playback and mobile devices, and switch to MKV when the file is headed for archiving, multi-language releases and media servers. Need a different target? The full Video Converter supports every format listed below.

MP4 to MKV FAQ

Is MP4 to MKV lossless?

Not bit-for-bit: the video is re-encoded, but keeping the source codec and bitrate (the default) makes the MKV visually identical to the MP4.

Why would I convert MP4 to MKV?

For media-server libraries, to add multiple subtitle or audio tracks, or to preserve chapters and metadata that MP4 handles poorly.

Is this MP4 to MKV converter free?

Yes. Converting MP4 to MKV on MediaConverter.io is completely free, with no watermark, no sign-up and no daily conversion limit.

Are my MP4 files uploaded to a server?

No. The converter runs inside your browser using WebAssembly and WebCodecs, so your .mp4 file is read and converted on your own device. Nothing is uploaded, which keeps private recordings private and means there is no waiting in an upload queue.

Is there a file size limit for MP4 to MKV?

No fixed limit. Because processing happens locally, the practical limit is your computer's memory and patience; multi-gigabyte MP4 files convert fine on a desktop browser. Very large files take longer on phones.

Will converting MP4 to MKV reduce quality?

The video is re-encoded into MKV. Keep the source codec, resolution and bitrate (the defaults) and the result is visually the same as your MP4; lowering the bitrate or resolution is what reduces quality, and you control that trade-off in the settings panel.

Which browsers support the MP4 to MKV converter?

Current versions of Chrome, Edge, Firefox and Safari on desktop all work. Chrome and Edge are fastest because they expose hardware-accelerated WebCodecs decoders.