Matroška File Containers (MKV)

This is an open-source project for a container supporting an unlimited number of media tracks in a single file. This container is extremely versatile and free of royalties. This makes it very attractive as a starting point for other container designers to use and extend.

Although the Matroška format is not from a Russian heritage, it is so named because the internal nested structure resembles the small hollow wooden dolls from Russia. Opening each doll reveals another smaller one inside. This illustrates the way that objects are owned by other objects in a hierarchical tree structure inside the container.

Internally, the file is object structured like QTFF or ISOBMFF. The objects in a Matroška file are called elements and are documented at the Matroška web site:

The element types are more rigidly defined than ISOBMFF. Matroška element codes are arguably less mnemonic and have a logical pattern when expressed in the hexadecimal notation. The ISOBMFF and QTFF type codes are more humanly readable. At the application coding and inspection level, a symbolic lookup table can map these values to more easily understood texts. Some older element types have been deprecated where they were sub-optimally designed or were rarely used.

The Matroška format is standardized as RFC 9559 and has the following features:

• Fast seeking in the file for navigation.
• Chapter entries that work like DVD scenes.
• Full metadata (tags) support.
• Selectable subtitle/audio/video streams.
• Expandable by adding new modules.
• Error resilience allowing playback to be resynchronized.
• Can be streamed over the Internet and local networks.
• Supports DVD-like menus for content selection.

There have so far been four versions of the Matroška format. Version 4 is current and maintained. The older versions are stabilized with no changes being released. Make sure that you are using the latest version.

Extensible Binary Meta Language (EBML)

EBML is a binary container format designed for audio/video storage. Structurally it is similar to XML but more compact. It uses a storage-efficient approach to build nested elements with identifiers, lengths, and values. This is sometimes described as Key-Length-Value (KLV) coding.

The RFC 8794 specification for EBML is updated by the later RFC 9559 that describes the Matroška container format. This fixes an oversight with one of the element IDs as an erratum. This is necessary because the affected element is used in Matroška but was previously reserved in EBML.

Content Organization - Levels

Content can be tagged and organized into a hierarchy of nested item levels. This structure can be applied to audio or video content. Interesting user interface possibilities arise from this kind of content organization:

Content Arrangement - Track Types

The following track types are supported within a Matroška file. They are all described in RFC 9559:

Create and register your own track types with the IANA if none of these meets your needs. Consult RFC 8126 for guidelines on how to document your new track type for submission.

IANA Registries

The IANA maintains the following registries for the Matroška project. The changes to the registries are managed by the IETF:

Relationships To Other Formats

Matroška was forked from the Multimedia Container Format (MCF) open-source project in 2002. Matroška uses Extensible Binary Metalanguage internally to organize the content. It has been around for quite some time now and is a mature technology.

The WebM container was initially based on Matroška to carry VP8 video and Vorbis audio.

Microsoft added support for HEVC video carried in a Matroška container in Windows 10.

Media Type Identifiers

Applications should recognize the legacy types but they should not be used for new projects now that the official types without the ‘X-’ prefix have been defined.

File Name Extensions

These are the file name extensions for generic Matroška container files. When the files are used for specialized applications they may change the file name extension so they can ‘own’ the file.

Relevant Standards

These standards are relevant when you are using or developing Matroška container formats:

Applying Matroška Containers

All things considered, the Matroška format is probably a very good choice if you are building a workflow infrastructure. It has few limitations and because it is open sourced there are no license fees. The source code is available and easy to customize.

Matroška is designed for future expansion. New elements can be added and the IANA registries show how the internal format and structure can be data driven.

The open-source nature of Matroška virtually guarantees that it will be a successful format as is already evident by the way it is deployed natively or used as the basis for other new formats.

These Appendix articles contain additional information you may find useful: