How to set default application for viewer pane video preview?

How can I set the default video viewer for the viewer pane? (formats like mp4, webm)
On another client I think MPC is used, but I can't figure out setting this up, on my laptop client. When I select a video file, I see the correct video play/seek bar for at split second, and then it changes to "Windows Media Player Legacy". I just "uninstalled" the legacy player, to try to force another default player but instead I see the correct video play bar for a split second, and then it changes to a static thumbnail image. I am pretty lost :confused:

This page has details: HOW TO: Enable/fix playback of various media formats in Opus