MKV file format, also known as Matroska file format, is a multimedia container envelope for video, audio and subtitle files, allowing the user to store a complete movie with subtitles or CD in a single file. MKV is an alternative to the popular formats Audio Video Interleave (AVI), Apple’s Quicktime (MOV) and Moving Pictures Experts Group (MPEG), but with new features in many areas. It supports OGG audio and variable framerate video. Nowadays when every container format in use fulfills some or even many of the features desired in a container format, MKV aims to become the standard of multimedia container formats. MKV is based on EBML (Extensible Binary Meta Language) which enables it to be highly flexible for meeting future needs.
Open source is one significant advantage of MKV. That means it is freely available to everybody over the world, and the technical specifications describing the bitstream are open to the public, even to those companies who want to support it in their products. Most other container formats contain mostly proprietary code, developed solely by the originating company and licensed parties. The open standards project of MKV makes it highly potential for more creative solutions and broader implementation.
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Many people find their video player software cannot work with MKV file. Well, not every video player supports MKV files. MKV file contains multiple streams (video, audio and subtitles) which are likely compressed and have been made with an encoder. A codec is required to play these streams. So you may need to install decoding software and filters to playback depending on what player you use. For most MKV files people find, the Video Lan Client (VLC), one player which is not based on DirectShow, supports for MKV files without need of plugins or special codes. Other options are Mastroska’s own CorePlayer Pro and Mobile.