It's not simply blurring a static background image. The process is to enlarge cover art (or thumbnail) to full size/stretched then apply a radical Gaussian blur.
The end result is much like a fade effect background that's used for all sorts of large-screen visuals (ppt slides etc. etc.), but the key is that because the colours are from the focused source, it's coordinated. I believe Spotify and Plex use this 'trick' for their TV interfaces.
I was able to try it for audio cover-flow/playing now etc. in MC and it looked very good - much better than the alternative of either a static background or fan art that's not colour coordinated in anyway and far too busy/distracting.
Unfortunately, this is a bit of a pain to do in Theatre View
- Create the blurred backdrops for every cover – could be batch processed I guess
– Place the jpg in the album folder,
- Enable media slideshow in themes and disable all online content sources.
There are several downsides – one is that if you store Folder.jpg (or any pic file in a recognised format for that matter) in the album folder it includes that as a backdrop and cycles between them as a slideshow (which looks terrible and defeats the object of having a specific ‘backdrop.jpg’).
This setting combination also doesn’t work at all for video files. This has been reported and discussed many times but never resolved.
Plus, even if fixed/implemented for video files, it wouldn’t work for thumbnails/photos where there isn’t a containing folder for every file as such.