MP4 thumbnails missing in Windows

[Bencuri]

I have a problem that in Explorer, I cannot see thumbnails for MP4s. Other video formats have thumbnails, but the ones for MP4s doesn't show up. It has been going on for a while, don't remember since when. What can be the problem? Windows Media Player plays MP4s fine, anyway.

[butterw]

Something broken in Windows thumbnails probably. No idea if it is fixable, I just use Icaros instead.

[Bencuri]

K-lite codec pack fixed it. It was a registry problem. There has to be a different registry key than the one that was present in my registry. It is different than the ones suggested online. K-lite adds the proper key and now it works even when the codec pack is uninstalled.