Turns out, it just using Codec Tweak Tool to do this thumbnail option. No need to install the codec pack. Just use Codec Tweak Tool -> Thumbnail Settings.[/quote]
Sorry to bring back an old thread. I left out some critical info.
When I switched to Windows 8, and just now needed thumbnails, I noticed I was missing a ton again. Forgetting what I did before, I remembered that I posted about this before. Trying the above tool (Codec Tweak Tool), did not work on it's own. In fact, Codec Tweak Tool's Thumbnail option isn't even clickable. I must of had something left over from the k-lite codec pack.
Turns out you still need to install Icaros. Install and activate Icaros (You need to Deactivate to change settings). What I really love about Icaros is that you can pick a percentage (default 25%) spot where the thumbnail gets pulled from within the movie file (1 hour movie gets it's thumbnail from around the 15 minute mark when set to 25%). I've only ran into a few .mpg's that are showing black frames (or frame 1. even when Dopus's Movie plugin is set to generate thumbnails and skip black frames).
Now you can run Codec Tweak Tool -> Thumbnails. Select All and Save.
If you want to use Dopus's Caching, then go to Preferences -> Viewer -> Viewer Plugins. Select Movie -> Configure. Make sure "Generate Thumbnails" is checked and "Skip over initial black frames" is UNchecked (I'm guessing it might interfere with the 25% Icaros setting if left checked).
If you want Windows to handle the video thumbnail caching, then UNcheck "Generate Thumbnails" in the above Movie plugin.
At first, I didn't think Dopus's would use this Icaros to help with the thumbnails, but it looks like it does from my testing. Is that because Icaros is a Windows Shell Extension?
Anyway, hope this helps.