Does editing an MKV re-encode the video?
No. The file is rebuilt with a stream copy, so every video, audio and subtitle stream is carried over unchanged. Only the container and its labels are new.
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Edit MKV titles, track names and flags
Fix “Unknown” audio, rename subtitle tracks, choose the default language and mark forced subtitles, then save a stream copy of the same file.
To edit MKV metadata, open the file here, go to Edit & clean, change the title or a track’s Name, Language, Default or Forced setting, and press Download new file. The new MKV is a stream copy: the same video, audio and subtitles in a rebuilt container, with nothing re-encoded.
These are the fields that decide what a media player does on its own: which audio plays first, which subtitles appear without being asked, and what the track menus say. A film whose audio menu reads “Track 1, Unknown” or whose foreign-language scenes play without their subtitles is almost always a metadata problem, not a broken file.
It works in any modern browser, Windows, Mac, Linux, iPhone or Android, and the file never leaves your device. If you have MKVToolNix installed, its header editor does the same job on a computer; this page compares the two below.
How to edit an MKV file’s metadata
Open the MKV
Press Open a file (Ctrl/Cmd+O) or drop the file on the page. WebM files open the same way, since WebM is a form of Matroska.
Review the tracks
Open Tracks to see every video, audio and subtitle track with its codec, language, name and flags. Check which ones are marked default now.
Edit titles, names and flags
In Edit & clean, change Title for the whole file, then each track’s Name, Language, Default and Forced. Use Remove track to drop a subtitle or data track you do not want.
Save the stream copy
Press Download new file (Ctrl/Cmd+S). FFmpeg loads in the browser the first time (about 10 MB) and rebuilds the file around the same streams. What changed lists each edit.
The MKV fields that matter, and what players do with them
Matroska keeps its metadata in a few clearly separated parts: segment information for the whole file (the title and the date it was muxed), one track entry per stream, a chapters list, and optional tags. The track entries are where the useful settings live.
| Field | What the Matroska spec says | What it changes in practice |
|---|---|---|
| Title (segment title) | The general name of the file | Shown by VLC and some players instead of the file name |
| Track Name | A human-readable track name | The label in audio and subtitle menus, e.g. “Commentary” or “English SDH” |
| Track Language | The track’s language; the old element defaults to English when missing | Automatic selection by language preference; how the menu names the track |
| Default | The track is eligible for automatic selection | Which audio and subtitle track a player starts with when you have no preference set |
| Forced | Subtitles only: eligible for automatic selection when it matches the viewer’s language, even with subtitles off | Shows foreign-language lines (signs, a scene in another language) without turning on full subtitles |
Default and Forced in a typical film
- Main audio in the original language: Default on.
- Commentary track: Default off, Name “Director’s commentary”.
- Full English subtitles: Default off, so they appear only when chosen.
- English forced subtitles (just the alien dialogue or the letter on screen): Forced on, Name “English (forced)”.
Only one track of each type should normally be default. Players differ in how strictly they honour Forced: Plex users report that it depends on the server’s subtitle settings and the languages of both audio and subtitles, so set the languages correctly as well as the flag.
Language codes
Matroska stores languages as codes rather than words. The classic form is a three-letter ISO 639-2 code; newer files can also carry a BCP 47 tag, which allows regional variants. When a track has no language at all, the specification treats it as English, which explains some odd menus.
| Language | Three-letter code | BCP 47 example |
|---|---|---|
| English | eng | en, en-GB |
| French | fre or fra | fr, fr-CA |
| German | ger or deu | de |
| Spanish | spa | es, es-419 (Latin America) |
| Japanese | jpn | ja |
| Chinese | chi or zho | zh-Hans, zh-Hant |
| Undetermined | und | und |
If Plex, Jellyfin or Kodi shows “Unknown”, the track is usually marked und. Setting the right Language fixes the label and lets the player pick the track from your language preference.
How the new MKV is written
MKV files are rebuilt with ffmpeg.wasm, FFmpeg compiled to run inside the browser and served from this site. It copies every stream as it is (-c copy), writes the new title, names, languages and flags, and carries the chapters across. Nothing is decoded or compressed again, so quality is identical.
- Time depends on file size rather than length of video: the whole file is read and written once.
- A very large Blu-ray remux needs a lot of browser memory; on a phone, a desktop tool may be more comfortable for those.
- Some fields have no place in Matroska and are switched off: Location, Make, Model, cover art and 360° metadata.
MKVToolNix’s mkvpropedit edits the headers in place, “without a complete remux” in its own words, which is quicker on huge files. The browser editor rebuilds the container instead, so the output is a new file and your original stays untouched.
The same job in MKVToolNix or FFmpeg
MKVToolNix is the reference toolkit for Matroska. Its GUI has a header editor (open a file there, change the track’s name, language or flags, and save), and its command-line tool does the same:
mkvpropedit film.mkv --set "title=The Long Walk" --edit track:a1 --set language=eng --set name="Stereo" --edit track:s1 --set flag-default=0 --edit track:s2 --set flag-forced=1
track:a1 means the first audio track and track:s2 the second subtitle track. Setting Default on one track does not clear it on another, so turn the old one off explicitly. Run mkvpropedit --list-property-names to see every property you can change.
ffmpeg -i film.mkv -map 0 -c copy -metadata title="The Long Walk" -metadata:s:a:0 language=eng -disposition:s:0 0 -disposition:s:1 forced fixed.mkv
FFmpeg writes a new file, as this site does. The browser editor is handy when you have no desktop tools, are on a phone, or want to see each track and flag explained before you change it. For MP4 files, use the MP4 metadata editor instead.
MKV metadata: questions people ask
How do I make English the default audio track?
Turn Default on for the English audio track and off for the others, and make sure its Language is English. Players then start with it unless your own language settings say otherwise.
What are forced subtitles?
A subtitle track meant to show even when subtitles are off, usually covering only foreign-language dialogue or on-screen text. Mark it Forced, give it the right language and a clear Name so players and people can tell it from the full track.
Why does Plex show my audio language as Unknown?
The track is most likely tagged und (undetermined) or not tagged. Set its Language here, save the new file and let Plex rescan it.
Can I edit MKV metadata on a Mac?
Yes, in Safari, Chrome or Firefox, with no install. MKVToolNix also runs on macOS if you prefer a desktop app.
Can I add a location or camera model to an MKV?
No. Matroska has no standard fields for them, so those options are switched off for MKV and WebM. MP4 and MOV do support them.
Can I get the subtitles out instead?
Yes. In Tracks, text subtitle tracks have Download subtitles; see extract subtitles from a video.