I think the video strip down the left of video thumbnails in KDE is hideous, and so here is how to get rid of it:
1. Replace the files in [kde]/share/apps/videothumbnail/ with these (for instance, on Mdk it's /usr/share/apps/videothumbnail.. may also be /usr/local/share/apps/videothumbnail or something completely different - ymmv.
Note: just deleting the originals doesn't seem to work.
2. Delete the contents of ~/.thumbnails in order to force an update of all your video thumbnails.
My desktop -
Windec: Whid preview
KDE style: Plastik
GTK style: GTK-QT Theme Engine
KDE icons: nuvola
GTK icons: Nuvola SVG
Firefox icons: Nuvola (via my Small Nuvola for Firefox)
Font: Bitstream Vera Sans
Panel applet: Kicker Pager