What is a .mkv file?
Matroska Video · Video · Matroska (open source) · 2002
MKV is a flexible open container that can hold almost any video, plus many audio tracks, subtitles and chapters in one file. It is popular for high-quality movies and archives, though it is not natively supported in most browsers.
What is a .mkv file used for?
Matroska can wrap essentially any codec and pack in multiple audio languages, several subtitle tracks and chapter markers, which makes it the format of choice for full movie files.
The project started in 2002, led by Steve Lhomme, and the name comes from the Russian matryoshka nesting dolls, because the file is built from elements nested inside one another. Underneath sits EBML, the Extensible Binary Meta Language, a binary cousin of XML that lets new element types be added without breaking older players. Matroska is an open standard with no licence fee, which is why it spread through the enthusiast and archiving world rather than through consumer devices.
The family shares one structure and splits by extension: .mkv holds video, .mka audio only, .mks subtitles only and .mk3d stereoscopic 3D video. Google's WebM is a deliberately restricted subset of the same format, limited to VP8, VP9 or AV1 video with Vorbis or Opus audio, which is why an MKV and a WebM both start with the identical EBML header 1A 45 DF A3 and a byte check alone cannot tell them apart.
Support is good on the desktop and patchy elsewhere. Windows 10 and 11 play MKV in the built-in Media Player, VLC, mpv, IINA, Plex, Kodi and Jellyfin all handle it, and most video editors import it. Browsers do not officially support Matroska, iPhones need VLC or Infuse rather than the built-in player, and smart TVs vary by brand and by which codec the file actually contains.
When something refuses an MKV, you usually do not need to re-encode it. If the video and audio inside are already H.264 and AAC, remuxing with MKVToolNix or the command ffmpeg -i in.mkv -c copy out.mp4 rewrites the wrapper in seconds with no quality loss at all. Re-encoding with HandBrake is only necessary when the codec itself is unsupported, for example H.265 or DTS audio on an older device.
MKV is easy to mistake for a codec. It is not one: an MKV can be tiny or enormous, sharp or soft, depending entirely on what was put inside it. VLC's Tools then Codec Information panel lists every track in the file, which is the fastest way to see why a particular player is struggling.
What opens a .mkv file?
The .mkv format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- Media Player (Windows 10 and 11)
- VLC
- MPC-HC
- mpv
macOS
- VLC
- IINA
- mpv
Linux
- VLC
- mpv
- Totem
iPhone and iPad
- VLC for iOS
- Infuse
- nPlayer
Android
- VLC for Android
- MX Player
Web
- Not natively, convert to MP4 or WebM
Open a .mkv file step by step
- Confirm the file really is a .mkv. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with Media Player (Windows 10 and 11) or VLC.
- On Mac, use VLC or IINA.
- On Linux, try VLC or mpv.
- On an iPhone or iPad, use VLC for iOS or Infuse.
- On Android, use VLC for Android or MX Player.
- Still stuck? Convert the .mkv to MP4, which opens more widely.
Why can't I open my .mkv file?
Almost always because no installed app understands MKV. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .mkv at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .mkv file
You can convert a .mkv file to MP4, WebM, MOV.
MKV to MP4 is usually a remux, not a re-encode: ffmpeg -i in.mkv -c copy out.mp4 finishes in seconds without touching the video. Subtitle tracks and chapters that MP4 does not support are the part that gets left behind.
What is the .mkv file signature (magic bytes)?
A .mkv file starts with the hex bytes 1A 45 DF A3. Programs identify MKV by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for MKV. For a full breakdown, see the Matroska / WebM file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| 1A 45 DF A3 | 0 | - | EBML header (Matroska/WebM) |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .mkv file?
MKV is a flexible open container that can hold almost any video, plus many audio tracks, subtitles and chapters in one file. It is popular for high-quality movies and archives, though it is not natively supported in most browsers.
Why won't my MKV play on my phone or browser?
MKV is not natively supported by most browsers and many phones. Play it in VLC, or convert it to MP4.
Can I convert MKV to MP4 without losing quality?
Yes, if the streams inside are already MP4-compatible, which for H.264 video and AAC audio they usually are. Remuxing with MKVToolNix or ffmpeg -i in.mkv -c copy out.mp4 copies the streams into a new container without re-encoding, so quality is identical and it takes seconds. Only an unsupported codec forces a real re-encode.
What plays MKV files on an iPhone or iPad?
The built-in Photos and Files players do not open MKV. Install the free VLC for iOS, or Infuse, then open the file from Files, an AirDrop or a network share. The same applies to Apple TV, where Infuse and VLC are the usual answers.
Is MKV better quality than MP4?
No, and it cannot be. Both are containers, so quality is decided by the codec and bitrate stored inside. MKV wins on features (multiple audio languages, switchable subtitles, chapters, any codec) and MP4 wins on compatibility.
What is the difference between MKV and WebM?
WebM is a restricted profile of Matroska built for the web: only VP8, VP9 or AV1 video with Vorbis or Opus audio. Every WebM is structurally a Matroska file, which is why both begin with the same EBML signature 1A 45 DF A3, but not every MKV qualifies as a WebM.
Why does my MKV play with no sound on my TV?
The television understands the video codec but not the audio track, most often a Dolby Digital or DTS surround stream. Play it through VLC or Kodi instead, or convert just the audio to stereo AAC, which leaves the video untouched.
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