matroska

Matroska is an open, free multimedia container format designed to store an unlimited number of video, audio, subtitle, and metadata tracks in a single file. It is based on EBML, Extensible Binary Meta Language, which gives Matroska a flexible, extensible structure for organizing data.

A Matroska file can contain multiple video and audio tracks, multiple subtitle tracks in different languages, chapters, and attachments such as cover art. The format supports advanced features such as metadata tagging, track-level codecs, soft- and hard-subtitles, and efficient random access through indexing.

File extensions include .mkv for video files, .mka for audio-only files, and .mks for subtitles. The project began in the early 2000s, initiated by Steve Lhomme, and is developed by a community of volunteers. The most widely used implementation is MKVToolNix; numerous media players and tools (such as FFmpeg, VLC, and mpv) support Matroska files.

Matroska's design influenced the WebM project, a subset used for web video; Matroska itself remains a general-purpose container used for archiving and distributing HD video content. It is considered open and royalty-free, with the specification publicly available to developers.