hdrsample.mkv

Matroska video Reference

A .mkv file contains video, audio, and subtitles in the Matroska container. The open format holds almost every codec and many tracks in one file. Media players such as VLC read it directly, and Windows supports it since Windows 10. The related extension .mka marks audio-only files. The format is common for high-definition video.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.