Follow this guide to add support for additional video formats. This should enable better support for 4k and HEVC x265 videos on Windows 7/8/8.1/10 and allow opening of .mkv files.
- Download and install LAV filters for x86 AND x64: https://github.com/Nevcairiel/LAVFilters/releases OR https://www.fosshub.com/LAV-Filters.html (run the installer as admin!)
- Restart Wallpaper Engine.
- Optionally force Wallpaper Engine to use DirectShow with LAV for videos by default, change the video framework option to Prefer DirectShow. Open Wallpaperr Engine Settings -> Geneal -> Media -> Video Framework -> Prefer DirectShow LAV
- It it worked, you will see a red LAV decoder icon[breakthrusoftware.com] in the tray. You can disable this icon in their options too.