What is the MKV file format?
Files with the .mkv extension contain video, audio, and subtitles collected in a single multimedia container. This open-standard format was established in 2002 as the Matroska project, led by Steve Lhomme, and is based on a predecessor format - the MCF multimedia container. Its binary structure relies on EBML (Extensible Binary Meta Language), which was formally standardized as IETF RFC 8794 in 2020.
Stored multimedia data may use various codecs - according to the specification, virtually any codec can be wrapped. The most widely used video codecs today include:
- H.264 (AVC - Advanced Video Coding)
- H.265 (HEVC - High Efficiency Video Coding)
- AV1 - an increasingly common royalty-free codec
.mkv is popular among movie enthusiasts; finding software supporting it is easy, and since Windows 10 it has been supported natively by Microsoft Windows. .mkv files are highly capable of recovering from damaged data and support streaming over HTTP and RTP protocols.
Google's WebM format (2010) is based on .mkv, but is restricted to a defined set of codecs - originally VP8 and VP9, with AV1 added later. A companion audio-only variant, .mka, and a subtitles-only variant, .mks, share the same container structure.
Security & safety
RISK: LOWMKV files contain media data, not executable code, so the file itself is low risk. Real-world dangers are adjacent: pirated-movie downloads disguised as codec installers or .mkv.exe double-extension executables, malicious subtitle files exploiting old player bugs (the 2017 'hacked by subtitles' vulnerabilities in VLC/Kodi - long since patched, keep players updated), and scam 'MKV codec packs'. Never install a codec a website demands; VLC needs nothing extra.
Format details
in a nutshellFULL NAMEMatroska Video
DEVELOPERMatroska.org (open-source project, started by Steve Lhomme)since 2002 (fork of the MCF project); EBML standardized as IETF RFC 8794 (2020)
CATEGORYVideo Files
MIME TYPEvideo/x-matroska
TYPEEBML-based multimedia container (binary)
STANDARDOpen · royalty-free
MAGIC BYTES · FILE SIGNATURE
OFFSET
00010203
HEX
1A45DFA3
ASCII
·E··
Shared with WebM (same EBML base); distinguish by the DocType element: "matroska" vs "webm"
Programs that open MKV files
Windows6 apps
VLC media player
Open-source Right-click the MKV - Open with - VLC. Plays everything with built-in codecs; switch audio/subtitle tracks from the Audio and Subtitle menus. 
MKVtoolnix
Open-source Not a player - the official Matroska toolkit to inspect, edit, split and remux MKV tracks (mkvtoolnix-gui, mkvextract). 
Media Player (Windows 11) / Movies & TV
Built-in Double-click - MKV plays natively since Windows 10 (2015). If HEVC video fails, install the 'HEVC Video Extensions' from Microsoft Store.
MPC-HC (clsid2 fork)
Open-source Lightweight classic player; drag the MKV onto the window. Original project ended 2017 - use the actively maintained clsid2 fork.
mpv
Open-source Minimal high-quality player; drag & drop the file. Cycle audio with '#' and subtitles with 'j'. 
macOS3 apps
VLC media player
Open-source Drag the MKV onto VLC. QuickTime Player cannot open MKV - VLC is the standard answer on a Mac. 
IINA
Open-source Modern native macOS player built on mpv; set as default for .mkv in Finder Get Info. 
Linux3 apps
GNOME Videos (Totem)
Open-source Default player on GNOME desktops; plays MKV if GStreamer codec packs are installed. 
Android2 apps
VLC for Android
Open-source Install from Google Play, open the file from the Video tab or a file manager.
MX Player
Freemium Popular MKV player with subtitle support; may need the separate AC-3/DTS codec pack for some audio tracks.
iOS2 apps
VLC for iOS
Open-source Transfer the MKV via Files/AirDrop/Wi-Fi share and play in VLC - the built-in iOS player does not support MKV.
OPlayer
Paid Long-standing iOS media player with MKV support; transfer files over Wi-Fi or Files app. Technical details
deep spec| Container encoding | EBML (Extensible Binary Meta Language) binary format |
| Magic bytes | 1A 45 DF A3 at offset 0 (EBML header); DocType element "matroska" distinguishes it from WebM |
| MIME type | video/x-matroska |
| Video codec support | Unrestricted; common codecs include H.264, H.265/HEVC, VP9, AV1, and MPEG-4 |
| Audio codec support | Unrestricted; common codecs include AAC, MP3, FLAC, AC-3, DTS, Vorbis, and Opus |
| Subtitle formats | SRT, SSA/ASS, PGS (Blu-ray), VobSub (DVD), and others embedded natively |
| Simultaneous tracks | Unlimited video, audio, and subtitle tracks in a single file |
| Chapter support | Named chapters with timestamps; multiple editions (ordered chapter sets) supported |
| Attachment embedding | Arbitrary files such as fonts, cover art, and ICC profiles can be attached within the container |
| Streaming | HTTP progressive download and RTP streaming supported by design |
| Error resilience | Cluster-based structure allows playback to resume after corrupt or missing segments |
| Seek index | Cue Points element enables fast random-access seeking without scanning the full file |
| Companion extensions | .mka (audio-only Matroska), .mks (subtitles-only), .mk3d (stereoscopic 3D video) |
| Platform support | Native in Windows 10+; broad Linux support via GStreamer/FFmpeg; macOS via third-party players |
| Relationship to WebM | Google's WebM (2010) uses the same EBML base but restricts codecs to VP8/VP9/AV1 and Opus/Vorbis |
| Tag and metadata support | Supports nested XML-like tags for title, language, date, rating, and custom fields per track |
| Released | 2002 (fork of the MCF project); EBML standardized as IETF RFC 8794 (2020) |
| Open standard | Yes · royalty-free |
| Specification | www.matroska.org |
MKV conversions
Possible
.MKV .MP4GUIDE
Yes, MKV converts to MP4 - and if your video is H.264 or H.265 with AAC or AC-3 audio, the fastest method is…
How to convert
.MKV .SRTGUIDE
Yes - MKV stores subtitle tracks directly, so extracting one to SRT takes seconds with mkvextract or FFmpeg…
How to convert
.MKV .AVIGUIDE
Yes, MKV can be converted to AVI - FFmpeg handles it in one command, but re-encoding to Xvid/MP3 is…
How to convert
.MKV .VOBGUIDE
Yes, you can convert MKV to VOB, but it requires DVD authoring software, not just a file converter -…
How to convert
.MKV .WMVGUIDE
Yes, MKV can be converted to WMV - FFmpeg does it in one command, but re-encoding is unavoidable and quality…
How to convert
.MKV .WEBMGUIDE
Yes - if the MKV already contains VP8/VP9/AV1 video and Vorbis/Opus audio, FFmpeg can remux it to WEBM in…
How to convert
.MKV .MP3GUIDE
Yes - FFmpeg can do it in one command; if the MKV's audio track is already MP3, the copy is lossless.
How to convert
Community Q&A
asked by usersNo questions yet - be the first to ask about MKV files.
Frequently asked questions
How do I convert MKV to MP4 without losing quality?
Remux it: copy the streams into an MP4 container without re-encoding, e.g. 'ffmpeg -i in.mkv -c copy out.mp4'. Works when the video is H.264/H.265 and audio AAC/AC-3 - which covers most files. Quality is identical because nothing is re-encoded.
Why won't my Smart TV play this MKV file?
Either the TV rejects the Matroska container or it lacks a decoder for a stream inside (commonly HEVC video or DTS audio). Remux to MP4, or re-encode the offending track (e.g. DTS to AC-3). Plugging in via USB vs DLNA can also change what the TV accepts.
Is MKV better than MP4?
Quality is identical for the same streams - both are just containers. MKV is more flexible (any codec, unlimited tracks, chapters, attachments); MP4 is far more widely supported by devices and editors. Choose by compatibility, not quality.
Why does my MKV have no sound?
The audio track uses a codec your device can't decode - usually DTS or AC-3 on TVs and phones. Play it in VLC (decodes everything) or convert the audio track to AAC.
How do I extract subtitles from an MKV?
Use mkvextract from MKVToolNix or FFmpeg to pull the subtitle track. Text tracks come out as .srt/.ass directly; Blu-ray PGS image subtitles need OCR with a tool like Subtitle Edit.
Can I play MKV on iPhone?
Not with the built-in player. Install VLC for iOS (free) and add the file via the Files app, AirDrop or VLC's Wi-Fi sharing - or remux the file to MP4 first.
Why does OBS record to MKV?
MKV survives crashes - an interrupted recording stays playable, unlike MP4 which corrupts without its final index. OBS can remux finished recordings to MP4 via File - Remux Recordings, losslessly.
References
1IETF RFC 8794 - Extensible Binary Meta Language (EBML)www.rfc-editor.org
2Matroska.org - Technical specificationswww.matroska.org
