Of course life wouldn't be interesting if everything just worked fine, and media preview is not exempt from the all prevalent law of the sod — occasionally. So if you find that xplorer² crashes while trying to preview media, or it cannot play some exotic audio/video format (or if video playback is broken, sound without picture), more often than not all it takes is getting the latest version of a good codec pack like K-Lite:
The standard version should be ok for most people and includes shell extensions for extracting media information (duration, artist etc) for detailed views and media search
xplorer² knows many popular media types which are (as of the latest version 3.5):
If you use some other format that isn't in the above list, and you are sure that you have the codec for it installed (the standalone windows media player can play it), you just need to add your media file extension to xplorer² audio or video list using the advanced settings editor (available from Tools menu or the ribbon's Options submenu under the leftmost FILE tab). If you have many extensions use commas to separate them.