Use VLC Media Player or another versatile player that supports the Matroska (MKV) container.
Convert multiple files of multiple format to mkv - Stack Overflow AgAD9wYAAlFmEFY.mkv
Based on your request, I cannot directly "open" or "look into" a specific local file named AgAD9wYAAlFmEFY.mkv as I do not have access to your personal files or a local file system. Use VLC Media Player or another versatile player