Many .mkv videos work fine: first time I have seen this problem: screen displays a sad face.
Questions:
- Has anyone experienced this problem? Lessons learned?
- How to determine if this is a codec problem?
To get a better understanding of the problem you are experiencing we need more information from you. Please see How to submit a useful support request - General - OSMC for advice on how to help us.
Can you play the .mkv on a different device?
What does ‘ffmpeg - i .mkv’ report?
That normally indicates a more serious issue (e.g. Lack of power supply or Filesystem issues)
As people said before provide debug logs and also as mkv is only a container format provide MediaInfo for the problematic file.
Please see the mediainfo section in How to submit a useful support request - General - OSMC