Use VLC Media Player or another versatile player that supports the Matroska (MKV) container.
Use a tool like MediaInfo to check the audio and video streams inside the file. AgAD9wYAAlFmEFY.mkv
However, if you are trying to view, check the content of, or convert this MKV video file, here is how you can do it: Use VLC Media Player or another versatile player