What is MKV? MKV (Matroska Multimedia Container) is an open standard container format designed to hold an unlimited number of video, audio, subtitle, and metadata tracks within a single file. Unlike simple formats that tie a single codec to a container, MKV is codec-agnostic: it can encapsulate H.264, H.265 (HEVC), VP9, AV1, and numerous audio codecs. This flexibility makes MKV especially popular among enthusiasts who need multi-language subtitles, multiple audio tracks, chaptering, and rich metadata. Its support for advanced features—such as embedded fonts for subtitles, attachments (like cover art), and robust error recovery—helps maintain playback integrity and preserve quality across device and platform variations.