MP4 to MKV Converter – Free Online

How to Convert MP4 to MKV Online

Drop your MP4 file

Drag and drop your .mp4 file onto the box above, or click Choose Files. The request is already filled in: “Convert this to MKV”.

Say how, if you want

The AI assistant uses sensible defaults. To choose the resolution, frame rate or bitrate yourself, say so in the request, for example “Convert this to MKV in 720p”.

Save your MKV file

The assistant opens with your file and converts it on your own device; the file itself is never uploaded. When the MKV file is ready, click Save. Prefer to set everything by hand, or batch-convert several files into a ZIP? The classic converter is one click away on this page.

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 already asked for: the AI assistant's request says MKV, so one drop does it. Want a particular resolution, frame rate or bitrate? Just say so.
Batch friendly: the classic converter on this page takes several MP4 files in one go and downloads them as a ZIP.
Free, no watermark: no sign-up, and 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 free, with no watermark and no sign-up. The AI assistant runs on a free daily allowance of assistant credits; the classic converter on this page has no daily limit at all.

Are my MP4 files uploaded to a server?

No. The conversion runs inside your browser using WebCodecs and FFmpeg compiled to WebAssembly, so your .mp4 file is read and converted on your own device and never uploaded, which keeps private recordings private and means there is no waiting in an upload queue. The AI assistant only sees what you type and basic facts about the file: its name, format, duration and size.

Is there a file size limit for MP4 to MKV?

There is no plan or account limit, but the converter loads the whole MP4 file into your browser's memory, so about 2 GB per file is the practical ceiling; larger files may fail to open. Long or high-resolution files also take longer, especially on phones.

Can I choose the MKV settings myself?

Yes. Ask the AI assistant for a resolution, frame rate or bitrate in your request. Audio and subtitle track selection, the codec list and every other setting are in the classic converter, one click away on this page.

Will converting MP4 to MKV reduce quality?

The video is re-encoded into MKV. Keep the source codec, resolution and bitrate (the defaults) and an ordinary 8-bit video is visually the same as your MP4, while a 10-bit, HDR or full-color (4:2:2 or 4:4:4) source can lose some color detail. Lowering the bitrate or resolution is what reduces quality, and you control that trade-off by asking for it (or in the classic converter's settings).

Which browsers support the MP4 to MKV converter?

It is built and tested on current desktop Chrome and Edge, which are also fastest because they expose hardware-accelerated WebCodecs video decoders. Recent Firefox and Safari releases support the same web APIs; if a file fails there, try Chrome or Edge.