BYTETOOLS

MP4 to MKV Converter

Convert MP4 to MKV instantly with zero quality loss. Streams are copied into a Matroska container, not re-encoded — free, private, in your browser.

Drop an MP4 video here or click to browseLossless remux — near-instant, no re-encoding, and your video never leaves your device.

The video and audio streams are copied bit-for-bit into the MKV container — no re-encoding, no quality loss, and the conversion takes only seconds even for large files.

What is the MP4 to MKV Converter?

The ByteTools MP4 to MKV Converter repackages an MP4 video into the Matroska (MKV) container without touching the video or audio data.

  • Lossless remux — video and audio are copied, never re-encoded
  • Near-instant, even for large files
  • 100% local processing — nothing is uploaded
  • Ideal for Plex, Jellyfin, Kodi and media libraries
  • Free and unlimited, no watermark

How to use the MP4 to MKV Converter

  1. 1

    Drop an MP4 video onto the box or click to browse for one.

  2. 2

    Click Convert to MKV — the streams are copied, not re-encoded.

  3. 3

    Download your MKV file when the near-instant remux finishes.

About the MP4 to MKV Converter

The ByteTools MP4 to MKV Converter repackages an MP4 video into the Matroska (MKV) container without touching the video or audio data. Because the streams are copied bit-for-bit rather than re-encoded, the conversion is near-instant — even for large files — and there is exactly zero quality loss. It is one of the fastest tools on this site.

MKV is the container of choice for media libraries, Plex and Jellyfin servers, and anyone who wants flexible support for multiple audio tracks, subtitles and chapters. Remuxing your MP4s into MKV keeps them ready for that ecosystem without re-compressing anything.

Everything happens 100% locally in your browser — your video is never uploaded to any server. Since no re-encoding is involved, even multi-hundred-megabyte files convert in seconds once the in-browser engine has loaded.

Frequently asked questions

Does converting MP4 to MKV lose quality?

No. This tool remuxes rather than re-encodes: the exact same video and audio bitstreams are moved from the MP4 container into an MKV container. The picture and sound are bit-identical to the original.

Why is MP4 to MKV conversion so fast?

Because no video encoding happens at all. Remuxing only rewrites the container metadata around the existing streams, which is limited by file-copy speed rather than CPU-hungry encoding, so even long videos finish in seconds.

What is the difference between MP4 and MKV?

Both are containers that hold the same kinds of video and audio streams. MKV is more flexible — it handles almost any codec, unlimited subtitle and audio tracks, and chapters — while MP4 has broader support on phones, TVs and web players.

Will the MKV file be bigger than my MP4?

It will be almost exactly the same size, usually within a fraction of a percent. Since the streams are copied unchanged, only the small container overhead differs between the two files.

Is my video uploaded anywhere?

No. The remux runs entirely in your browser using WebAssembly, so your file never leaves your device. There are no uploads, accounts or limits.

Related tools