MP4 to MKV Converter

Repackage MP4 into MKV to add subtitles and multiple tracks for media servers like Plex - lossless, in your browser.

About this converter

MKV (Matroska) is a flexible container that can hold multiple audio tracks, subtitle streams, and chapters in a single file - which is why media servers like Plex and home-theatre setups favour it. Converting MP4 to MKV repackages your video into that more capable wrapper.

Because it is just a container change, this is a lossless remux: the H.264/HEVC video and AAC audio are copied across unchanged, in seconds even on large files.

MP4 to MKV: good to know

Lossless: the streams are copied, not re-encoded, so quality is identical to the MP4.
MKV shines for media-server libraries (Plex, Jellyfin) and files with multiple audio or subtitle tracks.
Fast even on big files, because no re-encoding happens.

How it works

Drop your file(s) in the box above (or click to browse).
Make sure MKV is selected as the output.
Click Convert, then Download your file.

Frequently asked questions

How do I convert MP4 to MKV?

Drop your MP4 above, choose MKV as the output, and click Convert, then Download. It finishes quickly because it is a container change.

Is MP4 to MKV lossless?

Yes. It is a remux - the video and audio streams are copied into the MKV container without re-encoding, so quality is unchanged.

Why use MKV instead of MP4?

MKV can hold multiple audio tracks, subtitle streams, and chapters, which makes it ideal for media servers like Plex and for archived movies.

Will it take long?

No. Because nothing is re-encoded, even multi-gigabyte files convert in seconds.

Is it private?

Yes. The remux happens in your browser, so the file never leaves your device.

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