Format overview
What is an MKV file?
Matroska is an open multimedia container family. MKV normally carries video, MKA carries audio, and MKS carries subtitles. One MKV file can hold several audio languages, subtitle tracks, chapters, attachments, and detailed metadata.
MKV does not specify one video codec. It can contain H.264, HEVC, AV1, VP9, MPEG-2, or other streams, so playback depends on the codecs as well as Matroska support.
Compatibility
MKV playback and editing
Cross-platform players such as VLC handle a wide range of MKV files. TVs, game consoles, mobile apps, browsers, and editors vary: a device may accept MKV but reject a particular audio codec, subtitle format, bit depth, or video profile.
When troubleshooting, inspect every track instead of assuming the .mkv extension identifies the problem.
Practical use
When should you convert or remux MKV?
Remux MKV to MP4 when the existing video and audio streams are already compatible and only the destination container is the issue. Transcode when the destination cannot decode a track, the file is too large, or an editor needs an intraframe format.
Use Multi-track MKV when preserving several disc audio and subtitle tracks matters. Use MP4 for broad device and web support, or MOV and an editing codec for production workflows.