> Can anyone tell me how to view mkv video files in Thumbs?
For TP to play a video format, you need to have a codec for it on your system. The most recommended pack of codecs is K-Lite, available [link=https://www.codecguide.com/download_kl.htm]here[/link].
To make .mkv and other non-standard files visible in ThumbsPlus, you'll probably also have to make a filetype definition for that particular extension. In Options | Preferences | Filetypes, you can create and edit such definitions. For movie file types, in the File Type Configuration dialog, set the "equivalent to type" field to "mpg".
