Viewable movie format

I have recently added a bunch of movies in mkv format.  I’m able to view the movies on my LG tv via dlna with no problem.  But when i go to view it on my Roku 3 or if someone else is attempting to view the movies remotely from a different location, they’re unable to view certain movies for some reason.  Is there a work around to view all movies remotely or via the Roku 3?  Or do i have to download software & convert the files myself?

MKV is just a container file. Its possible certain movies are not viewable on just the Roku due to the way they were encoded into MKV. You could try to reencode the MKV file using a (free) program like Handbrake (or similar type programs) and see if that fixes the issue. I use Handbrake to encode files to MKV and MP4 for playback through a Roku 2 XS. Converted content always plays.