MKV files containing 4K video or high bitrate 1080p video may stutter or buffer if played via a USB 2.0 port (due to bandwidth limits) or over a weak Wi-Fi connection.
Check the menu to ensure they are turned on. can roku play mkv files
Open the app (download it from the Channel Store if you don't have it). Select Video and browse to your file. MKV files containing 4K video or high bitrate