MKV (Matroska Video)
The open container that fits unlimited video, audio, subtitle, and chapter tracks into one file without licensing fees.
| Full name | Matroska Video |
| Extension | .mkv |
| MIME type | video/x-matroska |
| Developer | Matroska project (founded by Steve Lhomme) |
| Released | December 2002 |
| Type | Video container format |
| Based on | EBML (Extensible Binary Meta Language) |
| Standard | IETF RFC 9559 (published 2024) |
What is a MKV file?
MKV is an open, royalty-free container format that can hold an unlimited number of video, audio, picture, and subtitle tracks in a single file. It was created in 2002 as part of the Matroska project and has become the dominant format for high-quality video on the open web. Unlike proprietary containers, any software can read or write MKV at no cost.
MKV is a container, not a codec. It wraps video streams, audio streams, subtitles, chapters, and metadata together without dictating how the content is compressed. The actual picture quality depends on the codec inside, such as H.264, H.265, AV1, or VP9. One MKV file might hold a single H.264 video track; another might hold the same video paired with five audio tracks in different languages and a dozen subtitle tracks. The container just organizes the pieces and tells the player how to synchronize them.
History
The Matroska project was announced on December 6, 2002, as a fork of the Multimedia Container Format (MCF). The split happened after disagreements between MCF lead developer Lasse Kärkkäinen and Matroska founder Steve Lhomme over adopting EBML, a binary derivative of XML, as the structural foundation. The name comes from the Russian word matryoshka, the nesting-doll toy, chosen to represent how the format nests multiple media streams inside one file. In 2024, the IETF published the format as RFC 9559, giving it formal internet standards status.
Container vs codec
An MKV file is built on EBML, which organizes data as typed elements: each element has an ID, a size descriptor, and binary content. The top-level EBML element is called a Segment. Inside the Segment, multimedia data is grouped into Clusters, each holding a few seconds of content. A SeekHead index near the start of the file lets players jump to any point without scanning the whole file. Tracks, Chapters, Tags, and Attachments are separate named elements within the Segment, so adding or removing a subtitle track does not require rewriting the video data.
What it is used for
- Storing high-definition and 4K video with multiple audio and subtitle tracks for home media libraries
- Distributing films and TV shows with optional dubbed audio and subtitles in many languages
- Archiving screen recordings and game captures where lossless or high-bitrate video is needed
- Packaging web video encoded in modern codecs like AV1 or H.265 before converting to a streaming format
How to open it
MKV files play natively in VLC Media Player on Windows, macOS, and Linux, and in the Windows 11 built-in player when the right codec is installed. Most smart TVs and media players such as Kodi, Plex, and Infuse also support MKV directly.
Pros and cons
Strengths
- Supports unlimited audio tracks, subtitle tracks, and chapters in one file
- Royalty-free and open standard, so any software can implement it freely
- No file-size limit, making it practical for long recordings and 4K content
- Works with virtually every modern video codec including H.264, H.265, AV1, and VP9
Trade-offs
- Not natively supported in most web browsers or Apple devices without conversion
- Streaming services and social platforms do not accept MKV uploads
- Some older TVs and media players skip it in favor of AVI or MP4
- File repair after a corrupt or interrupted download is harder than with MP4
Convert MKV files
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MKV FAQ
What is the difference between MKV and MP4?
Both are containers. MP4 has wider device support, especially on iPhones, smart TVs, and browsers, and is the standard for streaming. MKV supports more tracks and features with no licensing restrictions, making it better for archiving and local playback. Converting between the two is often just a remux with no quality loss.
Why won't my MKV file play on my TV?
Your TV likely supports the MKV container but not the codec used inside, most often H.265 or AV1. Converting the video stream to H.264 while keeping the MKV container, or converting the whole file to MP4, usually fixes playback on older TVs.
Does converting MKV to MP4 reduce quality?
Not if the video inside is already H.264 or H.265. In that case the conversion is a remux: the video data moves from one container to the other without re-encoding, so quality is identical. Re-encoding only happens if you change the codec, and that does reduce quality slightly.
Can MKV files contain subtitles?
Yes, and that is one of MKV's main advantages. An MKV file can hold multiple subtitle tracks in formats like SRT, ASS, or PGS. Players like VLC let you switch between them at runtime. MP4 supports subtitles too, but with fewer track formats and fewer simultaneous tracks.