MP4 to MKV converter

MKV is the format of choice for media servers like Plex and Jellyfin, for archives and for adding several audio or subtitle tracks later.

Drop a MP4 file hereThe converter loads in your browser.

What happens to your MP4

Matroska accepts every codec an MP4 can hold, so MP4 to MKV is always a remux: streams copied in seconds, nothing re-encoded.

Tip: Keep the MP4 too if you share files with iPhones: Apple devices do not play MKV without a third-party app.

How to convert MP4 to MKV

  1. Drop your MP4 file on the box above, or tap it to pick one. The engine (about 31 MB) loads once per visit.
  2. The converter reads the file's streams and shows which codecs are inside.
  3. Keep the defaults, or pick a quality and resolution.
  4. Press the button, wait for the progress bar, then download your MKV.

Prefer the command line?

This is the FFmpeg command the converter runs for a typical MP4 (h264 + aac). Paste it into a terminal with FFmpeg installed for batch jobs or files too big for a browser tab:

ffmpeg -y -i input.mp4 -map 0:v:0 -map "0:a:0?" -sn -dn -c:v copy -c:a copy output.mkv

Streams are copied (-c copy), so this runs at disk speed. Your own file may contain different codecs; the converter above detects them and adapts. For other jobs, ask the FFmpeg command helper.

Questions

Does MP4 to MKV lose quality?

No. It is a lossless remux.

Why convert to MKV at all?

Crash-safe recording, multiple audio/subtitle tracks, chapters and styled subtitles.

Is my MP4 file uploaded?

No. The MP4 is read from your device by FFmpeg running as WebAssembly in the page, and the MKV is written back to your device. No server ever receives it.

Is there a size limit for MP4 to MKV?

We set none. The practical limit is browser memory: roughly 2 GB of output on a computer, and much less on phones.