How can I make Windows 7 show thumbnails for MKV files?

Icaros 1.2.5 works, if it doesn't work alone, install Shark007 Codec Pack!

http://www.majorgeeks.com/Icaros_d7220.html

http://shark007.net/

1. Go to the Haali Media Splitter Properties.

2. Click the Options tab, expand Explorer integration and select Enable thumbnails extraction:

   

3. Set the value to Yes. You might want to configure the Thumbnails offset (a milliseconds value) to say, 10000 to give you more representative thumbnails.

4. Restart the machine.

It doesn't seem to work at first with Windows 7 64-bit.

You need to add the following lines to the registry:

[HKEY_CLASSES_ROOT\.mkv\ShellEx\{BB2E617C-0920-11D1-9A0B-00C04FC2D6C1}] 
@="{c5a40261-cd64-4ccf-84cb-c394da41d590}"

[HKEY_CLASSES_ROOT\.mkv\ShellEx\{e357fccd-a995-4576-b01f-234630154e96}] 
@="{c5a40261-cd64-4ccf-84cb-c394da41d590}"

Curiously, a whole day after applying those changes, thumbnails for mkv files began to show up in Explorer, so it does work (with Haali MKV Splitter on Windows 7 64-bit systems).

MediaPreview as suggested per lifehacker does a fine job, also for other formats such as ogg and 3gp.