Convert MP4 to MKV
Convert an MP4 into an MKV without re-encoding anything. This is the rare video conversion that costs nothing: the existing video and audio streams are copied straight into the new container, so what comes out is bit-for-bit the same picture and sound. Only the wrapper changes, and it finishes in seconds regardless of how long the video is.
Use this without the search next time. Prathom Workbench puts Prathom's tools in your toolbar.
Add to Chrome — freeDrop your MP4 file here, or click to browse
Up to 50 MB. Deleted automatically after 30 minutes.
What it does
- Streams copied, not re-encoded — identical quality
- Finishes in seconds on files of any length
- MKV holds subtitles and extra audio tracks
- No watermark and no sign-up
How to use MP4 to MKV
- 1
Add the MP4
Drop the file in or choose it from your computer. Files up to 50 MB, and no account is needed.
- 2
Convert
The video and audio streams are copied into an MKV container with `-c copy`. Nothing is decoded and nothing is encoded.
- 3
Use it
The MKV plays in VLC, MPV, Plex, Kodi and most media players, and is now ready to take subtitle or audio tracks.
A conversion that changes the envelope and nothing else
A video file is two separate things: the encoded picture and sound, and the container that describes where they are and how they fit together. Most conversions change the first. This one changes only the second.
MP4 and MKV can both hold H.264 video and AAC audio, which is what an MP4 almost always contains. So moving from one to the other does not require touching the streams at all — they are read out of the MP4's structure and written into the MKV's, unaltered. The technical name for this is remuxing, and it is the reason this page can promise something none of the others can.
How it works
The conversion runs -c copy, which tells ffmpeg to copy every stream rather
than decode and re-encode it. No frame is examined. No encoder runs. The output
holds the identical video and audio data in a different wrapper.
Two consequences follow, and both are unusual. The quality is not merely close to the original, it is the original. And the speed is bounded by how fast the file can be read and written rather than by how much video there is, so length barely matters.
Why anyone wants MKV
Not for playback — MP4 wins that comfortably. For what the container can carry.
MKV stores subtitles as selectable text tracks, several at once, in different languages. MP4's subtitle support is limited and players disagree about it. If you are adding subtitles to something, doing it in MKV is the difference between text a viewer can turn on and text burned permanently into the picture.
The same applies to audio: MKV holds multiple tracks cleanly, which matters for a second language, a commentary, or an isolated microphone alongside a room mix. It also handles chapter markers properly.
There is a practical reason too. MKV is written so that a recording interrupted by a crash or a power cut remains readable up to the point it stopped. An MP4 keeps essential index information that is written when recording ends cleanly, so an interrupted one can be left unplayable. That is why OBS and similar tools record to MKV and remux to MP4 afterwards.
Keep the MP4 if you need reach
MKV plays on desktop players and many televisions and not much else. Browsers do not, phones mostly do not, and older hardware does not. Because the remux is free in quality terms and nearly free in time, the sensible arrangement is to keep both and hand out whichever the situation needs.
Examples
Preparing a file to add subtitles to
MKV stores subtitles as selectable text tracks, which MP4 handles poorly. Remuxing first means the subtitle work does not cost you a re-encode.
A recording that needs a second audio track
MKV carries several audio tracks cleanly — a second language, a commentary, an isolated microphone. The video is never touched.
Frequently asked questions
Does this lose any quality?
No — and that is unusual enough to be the point of the page. The video and audio streams are copied from one container into another without being decoded, so every byte of picture and sound data is identical. Most conversions on this site re-encode and cost a little quality; this one does not, because nothing about the streams needs to change.
Why is it so fast?
Because the expensive part of a video conversion is decoding every frame and encoding it again, and neither happens here. The work is reading the streams out of one wrapper and writing them into another, which is roughly the speed of copying the file. A two- hour video remuxes about as quickly as a two-minute one.
Why would I want MKV instead of MP4?
For what the container can hold. MKV carries subtitles as real selectable text, several audio tracks in different languages, and chapter markers, all of which MP4 supports poorly or inconsistently. It is also more robust to an interrupted write, which is why recording software often defaults to it.
Will it still play everywhere?
Less widely than the MP4, and that is the trade. VLC, MPV, Plex, Kodi and most desktop players handle MKV without trouble, and so do many smart televisions. Browsers, phones and older hardware generally do not. Keep the MP4 if you need it to play on anything you do not control.