Can't play a video

[IriDium]

I've experienced this before. It usually occurs on files that have been downloaded from the internet and have dubious encoding.

You could run this through nkvnix tools and see if it throws up an error, but mkv files are just a container and they could contain anything.

Why it sometimes works and other times not, will be a case of checking the logs (good and bad) too see what it different.

I'd be interested to see if it is a power issue, but with RPi anything is possible.