Software :: Static Thumbnail Cache

When using file preview mode in konqueror within a folder with movies the system automatically generates snapshots with an app called "kffmpegthumbnailer" (10% into the movies). Say I'd like to create my own thumbnails for files that do not get a good representation automatically, where do I put these thumbnails?Apparently Konqueror uses the folder "~/.thumbnails" as a cache storage. (if this is deleted, all thumbnail previews are regenerated). But when I try to supply my own thumbnail into this directory, it won't get used, instead a default one gets generated (even though the thumbnail type, size and name are identical).

How can I trick the cache functionality into using my own prepared samples instead of generating them. I would have thought there was a logical override, for example by supplying your own ".thumbnail" folder for files you'd like more control over, but this does not seem to be the case.