MKV to MP4
Turn an MKV into an MP4.
Matroska files often will not play on a TV, a phone or an editor. Drop the MKV and get an MP4, made on your device without an upload.
Watch the sound: some MKV audio, such as Dolby Digital, cannot be read by a browser.
Drop a video here.
Drop a video here.Choose a video.
MP4MOVWEBMMKVNothing leaves this device.
Several files of one kind convert together.
How it works
Convert, and read the note it gives you.
1
Drop the MKV
A recording, a download or a rip. Multi-gigabyte files work if your device has the memory.
2
Keep Plays everywhere selected
If the video is H.264 and the sound AAC it is copied in seconds. VP9 and similar video is converted to H.264.
3
Check the result line
If a sound track could not be read, the file row says the sound was left out. Nothing is hidden.
Measured examples
What happens to the sound.
Four generated 10-second 720p clips: the same H.264 picture, each with a different sound track, in Matroska files.
| Test file | Size | Change | Time | Result |
|---|---|---|---|---|
| 10 s clip, AAC soundChrome | 1.9 MB → 1.9 MB | Same size | 180 ms | Video stream identical · Copied, no quality lost |
| 10 s clip, AC-3 soundChrome | 2 MB → 1.7 MB | 12 percent smaller | 190 ms | Video stream identical · Sound left out · The sound couldn't be converted and was left out |
| 10 s clip, Opus soundChrome | 1.9 MB → 1.9 MB | 3 percent smaller | 410 ms | Video stream identical · Sound converted |
| 10 s clip, Vorbis soundChrome | 1.8 MB → 1.9 MB | 4 percent larger | 400 ms | Video stream identical · Sound converted |
Measured on November 7, 2026 in Google Chrome 157, on Apple M1 Pro. Times run from pressing Convert to the result being ready, with the page already loaded. Likeness is PSNR against the original: higher is closer, and above 40 dB the difference is hard to see. Every test file was generated for these measurements, none is anyone else's work, and each is described on the About page.
The video was copied untouched in all four. AAC sound was copied too, in 181 milliseconds. Opus and Vorbis sound was converted to AAC. The AC-3 (Dolby Digital) clip came back with no sound at all, and the page said so on the file row. Length matched to within 40 milliseconds in every case.
Facts
What reaches the MP4.
Video
H.264 is copied. Other codecs, such as VP9 or AV1, are converted to H.264.
Sound
AAC is copied. Opus and Vorbis are converted to AAC. Dolby Digital (AC-3) and DTS cannot be read by the browser and are left out.
Subtitles and chapters
Not carried into the MP4. Keep the MKV, or use a separate subtitle file with your player.
Several sound tracks
The first track the browser can read is used, so a film with a track per language gives you one of them.
Good to know
The sound is the part that goes wrong.
MKV can hold almost anything. MP4 players expect a short list, and a browser can only handle part of it.
Why MKV does not play everywhere
Matroska is a flexible container used by OBS, video downloaders and disc rips. It carries many sound and subtitle tracks, but TVs, phones and many editors only understand MP4 with H.264 video and AAC sound.
Audio a browser cannot read
Films and rips often carry Dolby Digital (AC-3), Dolby Digital Plus or DTS sound. Neither Chrome nor WebKit, the engine behind Safari in our tests had a decoder for them, and we do not ship one, since those codecs are patent-encumbered. The video converts and the file comes back without sound, with a clear note.
If the MKV also has an AAC track, that track is kept. For a film you want to keep in 5.1, use a desktop player that plays MKV directly or a desktop converter that bundles an AC-3 decoder.
What comes across
One video track and the sound tracks the browser can read. Subtitle tracks are not copied into the MP4, so burn-in or an external file is the route if you need them. Frame rate, rotation and picture size are kept, except that very large pictures can be lowered if you choose a smaller resolution.
Recordings from OBS
OBS can record to MKV so a crash does not lose the file. When the recording is done, converting to MP4 gives you an editor-friendly copy. If it used H.264 and AAC, this is a repack that takes seconds for hours of footage.
When you do not need to convert
Plex, Jellyfin, VLC, Kodi and most Android players and set-top boxes play MKV directly, and for those a conversion only costs time and, if the video must be re-encoded, a little quality. Convert when the destination is fussier: Apple's Photos and QuickTime, a phone gallery, a web upload form, an editor that rejects Matroska, or a smart TV with a short list of supported files.
If something goes wrong
When it does not work.
The sound is the part that goes wrong, and the page tells you when it does.
The sound couldn't be converted and was left out
Why: The track is Dolby Digital, Dolby Digital Plus or DTS. The browser has no decoder for it, and we do not ship one because those codecs are patent-encumbered.
What to do: Use a desktop player that plays MKV directly, or a desktop converter that includes an AC-3 decoder.
The subtitles are gone
Why: MP4 files carry subtitles in a different way, and this page copies video and sound only.
What to do: Keep the MKV for watching with subtitles, or put the subtitle file next to the MP4 for your player.
The picture was converted and took a while
Why: The video was not H.264, for example VP9, and was re-encoded.
What to do: Nothing to fix. Converting is the slow case; a copy takes a fraction of a second.